Allan J. Bieber

THE RELEVANCE OF ANIMAL MODELS IN MULTIPLE SCLEROSIS RESEARCH

Multiple Sclerosis (MS) is a complex disease with an unknown etiology and no effective cure, despite decades of extensive research that led to the development of several partially effective treatments. Researchers have only limited access to early and immunologically active MS tissue samples, and the modification of experimental circumstances is much more restricted in human studies compared to studies in animal models. For these reasons, animal models are needed to clarify the underlying immune-pathological mechanisms and test novel therapeutic and reparative approaches. It is not possible for a single mouse model to capture and adequately incorporate all clinical, radiological, pathological and genetic features of MS. The three most commonly studied major categories of animal models of MS include: (1) the purely autoimmune experimental autoimmune/allergic encephalomyelitis (EAE); (2) the virally induced chronic demyelinating disease models, with the main model of Theilers Murine Encephalomyelitis Virus (TMEV) infection and (3) toxin-induced models of demyelination, including the cuprizone model and focal demyelination induced by lyso-phosphatidyl choline (lyso-lecithine). EAE has been enormously helpful over the past several decades in our overall understanding of CNS inflammation, immune surveillance and immune-mediated tissue injury. Furthermore, EAE has directly led to the development of three approved medications for treatment in multiple sclerosis, glatiramer acetate, mitoxantrone and natalizumab. On the other hand, numerous therapeutical approaches that showed promising results in EAE turned out to be either ineffective or in some cases harmful in MS. The TMEV model features a chronic-progressive disease course that lasts for the entire lifespan in susceptible mice. Several features of MS, including the role and significance of axonal injury and repair, the partial independence of disability from demyelination, epitope spread from viral to myelin epitopes, the significance of remyelination has all been demonstrated in this model. TMEV based MS models also feature several MRI findings of the human disease. Toxin-induced demyelination models has been mainly used to study focal demyelination and remyelination. None of the three main animal models described in this review can be considered superior; rather, they are best viewed as complementary to one another. Despite their limitations, the rational utilization and application of these models to address specific research questions will remain one of the most useful tools in studies of human demyelinating diseases.

Efficient central nervous system remyelination requires T cells

We demonstrate a role for immune functions in the spontaneous remyelination of central nervous system (CNS) axons after lysolecithin‐induced demyelination in the spinal cord. Rag‐1–deficient mice lack both B cells and T cells and show significantly reduced spontaneous remyelination compared with control mice of matching genetic background. Mice lacking or depleted of either CD4+ T cells or CD8+ T cells also exhibit reduced remyelination. These data indicate that T cells are necessary for efficient CNS remyelination. Thus, general nonspecific immunosuppression as a therapeutic approach for the treatment of CNS injury and demyelinating disease may have undesirable effects on subsequent tissue repair. Ann Neurol 2003;53:680–684

Transient Receptor Potential Vanilloid 1 is essential for cisplatin-induced heat hyperalgesia in mice

BackgroundCisplatin is primarily used for treatment of ovarian and testicular cancer. Oxaliplatin is the only effective treatment for metastatic colorectal cancer. Both are known to cause dose related, cumulative toxic effects on the peripheral nervous system and thirty to forty percent of cancer patients receiving these agents experience painful peripheral neuropathy. The mechanisms underlying painful platinum-induced neuropathy remain poorly understood. Previous studies have demonstrated important roles for TRPV1, TRPM8, and TRPA1 in inflammation and nerve injury induced pain.ResultsIn this study, using real-time, reverse transcriptase, polymerase chain reaction (RT-PCR), we analyzed the expression of TRPV1, TRPM8, and TRPA1 induced by cisplatin or oxaliplatin in vitro and in vivo. For in vitro studies, cultured E15 rat dorsal root ganglion (DRG) neurons were treated for up to 48 hours with cisplatin or oxaliplatin. For in vivo studies, trigeminal ganglia (TG) were isolated from mice treated with platinum drugs for three weeks. We show that cisplatin and oxaliplatin-treated DRG neurons had significantly increased in TRPV1, TRPA1, and TRPM8 mRNA expression. TG neurons from cisplatin treated mice had significant increases in TRPV1 and TRPA1 mRNA expression while oxaliplatin strongly induced only TRPA1. Furthermore, compared to the cisplatin-treated wild-type mice, cisplatin-treated TRPV1-null mice developed mechanical allodynia but did not exhibit enhancement of noxious heat- evoked pain responses. Immunohistochemistry studies showed that cisplatin-treated mice had no change in the proportion of the TRPV1 immunopositive TG neurons.ConclusionThese results indicate that TRPV1 and TRPA1 could contribute to the development of thermal hyperalgesia and mechanical allodynia following cisplatin-induced painful neuropathy but that TRPV1 has a crucial role in cisplatin-induced thermal hyperalgesia in vivo.

A recombinant human IgM promotes myelin repair after a single, very low dose

A recombinant human monoclonal IgM, rHIgM22, promotes the synthesis of new myelin when used to treat several animal models of demyelination. rHIgM22 binds to myelin and the surface of oligodendrocytes and accumulates at central nervous system lesions in vivo. The minimal dose of monoclonal IgM required to promote remyelination has a direct bearing on the proposed mechanism of action. A dose ranging study using rHIgM22 was performed in mice with chronic virus‐induced demyelination, a model of chronic progressive multiple sclerosis. The lowest tested dose of rHIgM22 effective at promoting spinal cord remyelination was a single 500‐ng intraperitoneal bolus injection. A time course study of spinal cord repair performed in chronically demyelinated mice revealed that remyelination plateaued by 5 weeks following treatment with rHIgM22. Two doses of rHIgM22 spaced 5 weeks apart did not increase the extent of remyelination over a single dose. The half‐life of rHIgM22 in the mouse systemic circulation was determined to be 15 hr; the human IgM serum concentration was close to zero by 48 hr following antibody administration. We propose that the specificity of rHIgM22 for myelin on living tissue targets the antibody to demyelinated lesions, initiating a long‐term reparative effect on the central nervous system.

Human antibodies accelerate the rate of remyelination following lysolecithin-induced demyelination in mice

Immunoglobulin‐based therapies are becoming increasingly common for the treatment of neurologic and autoimmune diseases in humans. In this study, we demonstrate that systemic administration of either polyclonal human immunoglobulins or specific human monoclonal antibodies can accelerate the rate of CNS remyelination following toxin‐induced demyelination. Injection of lysolecithin directly into the spinal cord results in focal demyelinated lesions. In contrast to other murine models of demyelinating disease, the mechanism of demyelination following lysolecithin injection is independent of immune system activation, and chronic inflammation at the site of the lesion is minimal. Administration of polyclonal human IgM (pHIgM) or a serum‐derived human monoclonal antibody (sHIgM22) resulted in approximately a twofold increase in remyelinating axons when compared to animals treated with saline or with antibodies that do not promote repair. Both pHIgM and sHIgM22 show strong binding to CNS white matter and oligodendrocytes, while antibodies that did not accelerate remyelination do not. This differential staining pattern suggests that enhanced remyelination may result from direct stimulation of oligodendrocyte remyelination by binding to surface receptors on oligodendrocytes or glial progenitor cells. We propose the use of human polyclonal IgM or specific human monoclonal IgM antibodies as potential therapies to enhance myelin repair following CNS injury and disease. GLIA 37:241–249, 2002.

A human antibody that promotes remyelination enters the CNS and decreases lesion load as detected by T2-weighted spinal cord MRI in a virus-induced murine model of MS

The human monoclonal antibody rHIgM22 enhances remyelination following spinal cord demyelination in a virus‐induced murine model of multiple sclerosis. Using three‐dimensional T2‐weighted in vivo spinal cord magnetic resonance imaging (MRI), we have therefore assessed the extent of spinal cord demyelination, before and after 5 weeks of treatment with rHIgM22, to determine whether antibody enhanced remyelination can be detected by MRI. A significant decrease was seen in T2 high signal lesion volume following antibody treatment. Histologic examination of the spinal cord tissue reveals that this decrease in lesion volume correlates with antibody promoted remyelination. To show that rHIgM22 enters the spinal cord and colocalizes with demyelinating lesions, we used ultrasmall superparamagnetic iron oxide particle (USPIO)‐labeled antibodies. This may be considered as additional evidence to the hypothesis that rHIgM22 promotes remyelination by local effects in the lesions, likely by binding to CNS cells. The reduction in high signal T2‐weighted lesion volume may be an important outcome measure in future clinical trials in humans.

Direct evidence that a human antibody derived from patient serum can promote myelin repair in a mouse model of chronic-progressive demyelinating disease

Certain human sera from patients with monoclonal gammopathies contain factors that induce myelin repair in animals with demyelinating disease. We hypothesize that antibodies functionally distinguish the serum of one patient from another. However, pooled normal polyclonal human IgM antibodies also induce remyelination. Definitive proof that specific antibodies are the biologically active components of serum is missing because unquestionably pure preparations of antibody molecules cannot be generated by fractionation. To demonstrate definitively that antibody is the biologically active component of patient serum, recombinant antibody was generated for evaluation in bioassays. The induction of remyelination in vivo requires milligram quantities of antibody. Consequently, an expression system was engineered to express high‐titer, recombinant human IgM antibodies in vitro. A resulting recombinant antibody (rHIgM22) was evaluated for its ability to induce remyelination in the Theilers virus mouse model of chronic‐progressive demyelinating disease. We demonstrate that a single recombinant monoclonal antibody recapitulates the key characteristics of patient serum, including binding specificity, the induction of calcium signals in oligodendrocytes in vitro, and the induction of myelin repair within demyelinated plaques in vivo. The rHIgM22 antibody provides a new venue for the analysis of mechanisms governing remyelination and may prove useful in the treatment of demyelinating diseases.

Remyelination-promoting antibodies activate distinct Ca2+ influx pathways in astrocytes and oligodendrocytes: relationship to the mechanism of myelin repair

Our laboratory has identified mouse and human monoclonal antibodies that promote myelin repair in multiple models of demyelinating disease. We have proposed that these antibodies promote remyelination by directly activating central nervous system glia. Intracellular calcium concentration was monitored using a Fura2 ratiometric assay. Repair-promoting antibodies induced distinct Ca2+ signals in both astrocytes and oligodendrocytes. Astrocyte Ca2+ signaling is mediated by a phospholipase C-dependent pathway while oligodendrocyte Ca2+ signaling is mediated via AMPA-sensitive glutamate receptors. An antibodys ability to induce Ca2+ signals is statistically correlated with promotion of myelin repair. These findings support the hypothesis that remyelination-promoting antibodies are acting directly at the surface of glial cells to induce calcium-dependent physiologic reparative function.

Antiapoptotic signaling by a remyelination-promoting human antimyelin antibody.

Stabilizing the survival of oligodendrocytes and oligodendrocyte precursors within and near lesions in patients suffering from multiple sclerosis (MS) and other demyelinating diseases is an important therapeutic goal. Previous studies have identified a human-derived monoclonal IgM antibody designated rHIgM22 that induces remyelination in a mouse model of MS. We provide evidence that this antibody, directed against myelin, induces antiapoptotic signaling in premyelinating oligodendrocytes and reduces caspase-3 activation and caspase gene expression in mice undergoing antibody-induced remyelination. This effect was dependent on calcium entry via CNQX-sensitive channels and on lipid raft integrity, and was correlated with suppression of JNK signaling. We conclude that rHIgM22 may induce remyelination via rescue of oligodendrocytes, and suggest that such autoantibody-mediated signaling may have important therapeutic implications for a variety of neurological diseases, including stroke and Alzheimers disease.

A neurochemical closed-loop controller for deep brain stimulation: toward individualized smart neuromodulation therapies

Current strategies for optimizing deep brain stimulation (DBS) therapy involve multiple postoperative visits. During each visit, stimulation parameters are adjusted until desired therapeutic effects are achieved and adverse effects are minimized. However, the efficacy of these therapeutic parameters may decline with time due at least in part to disease progression, interactions between the host environment and the electrode, and lead migration. As such, development of closed-loop control systems that can respond to changing neurochemical environments, tailoring DBS therapy to individual patients, is paramount for improving the therapeutic efficacy of DBS. Evidence obtained using electrophysiology and imaging techniques in both animals and humans suggests that DBS works by modulating neural network activity. Recently, animal studies have shown that stimulation-evoked changes in neurotransmitter release that mirror normal physiology are associated with the therapeutic benefits of DBS. Therefore, to fully understand the neurophysiology of DBS and optimize its efficacy, it may be necessary to look beyond conventional electrophysiological analyses and characterize the neurochemical effects of therapeutic and non-therapeutic stimulation. By combining electrochemical monitoring and mathematical modeling techniques, we can potentially replace the trial-and-error process used in clinical programming with deterministic approaches that help attain optimal and stable neurochemical profiles. In this manuscript, we summarize the current understanding of electrophysiological and electrochemical processing for control of neuromodulation therapies. Additionally, we describe a proof-of-principle closed-loop controller that characterizes DBS-evoked dopamine changes to adjust stimulation parameters in a rodent model of DBS. The work described herein represents the initial steps toward achieving a “smart” neuroprosthetic system for treatment of neurologic and psychiatric disorders.