Hubertus Köller

IMMUNOLOGICALLY INDUCED ELECTROPHYSIOLOGICAL DYSFUNCTION : IMPLICATIONS FOR INFLAMMATORY DISEASES OF THE CNS AND PNS

During inflammation of the central or peripheral nervous system, a high number of immunologically active molecules, including bacterial or viral products as well as host-derived cytokines, are released. Patients suffering from inflammatory CNS or PNS diseases often develop transient symptoms with a rapid recovery, which obviously cannot be accounted for by immunologically induced tissue damage. These observations led to the hypothesis that immunologically active molecules can affect directly the electrophysiological functions of neurons and glial cells. Evidence for this hypothesis came from in vitro studies showing that cytokines, such as interleukins or tumor necrosis factors, arachidonic acid and its metabolites, interfere with electrophysiological properties of neurons or glial cells. These molecules affect ion currents, intracellular Ca2+ homeostasis, membrane potentials, and suppress or enhance the induction and maintenance of long-term potentiation. Similarly, virus proteins from human immunodeficiency virus type I were found to alter intracellular Ca2+ concentrations of neurons and astrocytes by modulating either transmitter receptors and channels or membrane transporters. Cerebrospinal fluid from MS patients contains factors which increase Na+ current inactivation and thereby reduce neuronal excitability. Immunoglobulins in sera of patients suffering from multifocal motor neuropathy and from acquired neuromyotonia interfere with nerve fibers, inducing alterations of conduction. Increased knowledge of these mechanisms will help to explain the pathogenesis of neurological symptoms and may provide a rationale for new therapeutic strategies.

Subcutaneous self-infusions of immunoglobulins as a potential therapeutic regimen in immune-mediated neuropathies

Sirs: Intravenous immunoglobulins (IVIg) represent one of the mainstays in the treatment of chronic immune mediated neuropathies [1–4]. Although numerous studies demonstrated clinical efficacy of IVIg over the shortterm, the appropriate dose and route of administration for longterm maintenance therapy are not fully established [5]. Based on a small number of unblinded clinical trials and case reports clinical improvement is maintained with periodic application of IVIg. In clinical practice a regime of 0.4 g/kg BW every 4 weeks is usually chosen, which most of the patients receive by health care providers. Rapid subcutaneous infusions of immunoglobulins (SCIg), currently labelled and used for patients with primary immune deficiencies (PIDD), result in high and consistent serum IgG levels, are safe with very few systemic adverse reactions, whereas local tissue reactions are common, but usually mild and transitional. SCIg are comparable in the composition of their antibody spectrum to IVIg. The subcutaneous application can be easily learned by patients [6, 7]. In a recent study a preference for the subcutaneous route and for home therapy could be established in chronically treated patients with PIDD, when comparing IVIg with SCIg [8]. We report the experience with SCIg (Beriglobin , Aventis Behring, Marburg, Germany) in three patients with chronic immune mediated neuropathies. Patient number 1 is a 45–year old man with a biopsy proven chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) with clinical relapses [9]. At the time of SCIg treatment initiation the disease had been clinically evident for 2 years and previous treatment regimens included intravenous methylprednisolone, IVIg, and mycophenolate mofetil. The patient was still treated with oral methylprednisolone during SCIg application. Patient number 2 is a 64-year old woman with a 3 years history of a multifocal motor neuropathy (MMN) and primarily involvement of the upper extremities. Her previous therapy included IVIg. Patient number 3 is a 73-year old man with a 2 years history of MMN, primarily affecting the upper right extremity, who had responded to IVIg therapy. After obtaining informed consent, all patients were treated for 6 months with SCIg at a dose of 0.1 g/kg BW given once weekly; thus, the cumulative monthly dose was equivalent to the commonly applied IVIg dose of 0.4 g/kg BW. This translated into a volume of 40–50 ml of SCIg per week. For the application a battery-driven pump was used and per injection side 10–20 ml SCIg were applied at a speed of 10–20 ml/h. As outcome measures, safety, tolerability, and clinical disability, as defined by the INCAT disability scale and the MRC sum score, were assessed [10]. In all three patients the subcutaneous application was well tolerated, and we did not observe any local reactions at the injection sites. Patients’ satisfaction with the route of administration was high. In patient number 2 treatment was stopped after 9 weeks because of a generalized exanthema. A correlation between immunoglobulins and the skin reaction could not clearly be established, since a subsequent skin test with the product at a lower concentration was negative, and the subsequent application of IVIg was well tolerated. Further systemic side effects did not occur. The patient refused to continue treatment with SCIg; therefore the therapeutic regime with IVIg was re-initiated with no obvious clinical effect. Thereafter, immunosuppressive strategies, including cyclophosphamide, were started. Clinically, patient number 1 improved on the INCAT disability score as well as on the MRC sum score; no further relapses occurred. Oral steroids could be reduced, but not stopped, and the patient remained on lowdose oral steroids. Patient number 3 remained clinically stable throughout the entire observation period of 6 months and has not required any further therapy so far (Fig. 1). Our present findings indicate that the subcutaneous administration of immunoglobulins represents a safe therapeutic approach, which can be easily selfadministered by the patient at home. Moreover, the patients’ satisfaction was high, and the weekly subcutaneous mode of administration appeared more attractive than the monthly intravenous application. The number LETTER TO THE EDITORS J Neurol (2006) 253 : 1505–1506 DOI 10.1007/s00415-006-0258-0

Therapeutic effects of nonnucleoside reverse transcriptase inhibitors on the central nervous system in HIV-1-infected patients.

Summary: Psychomotor slowing predicts the development of HIV‐1‐associated dementia, AIDS, and death independent of immune status. We retrospectively selected all patients who showed pathologic psychomotor slowing as a sign of central nervous system (CNS) dysfunction before the onset of therapy and who were then treated with nonnucleoside reverse‐transcriptase inhibitors—either efavirenz (EFV) (n = 65 patients) or nevirapine (NVP) (n = 39 patients), each given in combination with two nucleoside analogues (NAs). Patients who were treated only with two NAs (n = 66) served as controls. Patients were observed for 6 months. Both EFV and NVP combinations improved CNS function as determined by electrophysiologic motor tests. The therapeutic effects of EFV and NVP did not depend on the type of NA added. Although results did not reach significance, NVP combinations were more effective than EFV combinations or therapy regimens with NAs alone in patients who were naive to all antiretroviral therapy. EFV and NVP combinations were equally effective in patients pretreated with highly active antiretroviral therapy, including protease inhibitors.

TNFα induces a protein kinase C-dependent reduction in astroglial K+ conductance

INCUBATION of cultured cortical astrocytes with tumor necrosis factor alpha (TNFα) led to a marked reduction of membrane potential. Here we report that this depolarization depends on activation of protein kinase C (PKC), since it could be blocked by the PKC antagonists staurosporine and H7 and it could be mimicked by direct activation of PKC using the phorbol ester phorbol 12-myristate 13 acetate (PMA). Analyses of whole cell currents revealed a reduction of inwardly rectifying K+ currents whereas K+ outward currents were not affected. We conclude that TNFα induces changes of basic electrophysiological properties of astrocytes which are similar to those induced by proliferation or an in vitro model of traumatic injury.

Ammonia-induced depolarization of cultured rat cortical astrocytes

Exposure of cultured rat cortical astrocytes to increased concentrations of ammonia has been shown to induce morphological and biochemical changes similar to those found in hyperammonemic (e.g., hepatic) encephalopathy in vivo. Alterations of electrophysiological properties are not well investigated. In this study, we examined the effect of ammonia on the astrocyte membrane potential by means of perforated patch recordings. Exposure to millimolar concentrations of NH4Cl induced a slow dose-dependent and reversible depolarization. At steady state, i.e., after several tens of minutes, the cells were significantly depolarized from a resting membrane potential of -96.2 +/- 0.6 mV (n = 83, S.E.M.) to -89.1 +/- 1.6 mV (n = 7, S.E.M.) at 5 mM NH4Cl, -66.3 +/- 3.6 mV (n = 9, S.E.M.) at 10 mM NH4Cl and -50.4 +/- 2.5 mV (n = 12, S.E.M.) at 20 mM NH4Cl, respectively. In order to examine the underlying depolarizing mechanisms we determined changes in the fractional ion conductances for potassium, chloride and sodium induced by 20 mM NH4Cl. No significant changes were found in the fractional sodium or chloride conductances, but the dominating fractional potassium conductance decreased slightly from a calculated 0.86 +/- 0.04 to 0.77 +/- 0.04 (n = 9, S.E.M.). Correspondingly, we found a significant fractional ammonium ion (NH4+) conductance of 0.23 +/- 0.02 (n = 10, S.E.M.) which was blocked by the potassium channel blocker barium and, hence, most likely mediated by barium-sensitive potassium channels. Our data suggest that the sustained depolarization induced by NH4Cl depended on changes in intracellular ion concentrations rather than changes in ion conductances. Driven by the high membrane potential NH4+ accumulated intracellularly via a barium-sensitive potassium conductance. The concomitant decrease in the intracellular potassium concentration was primarily responsible for the observed slow depolarization.

Chronic inflammatory demyelinating polyneuropathy : update on pathogenesis, diagnostic criteria and therapy

Purpose of reviewChronic inflammatory demyelinating polyneuropathy (CIDP) is a treatable but possibly underdiagnosed disorder of the peripheral nerve. This review covers the growing literature of the past years that deals with the pathogenesis, diagnostic criteria and treatment of CIDP. Recent findingsThe recent development of a biphasic animal model of experimental autoimmune neuritis may provide further insights into the pathogenesis of inflammatory demyelination of the peripheral nerve, such as in CIDP, and may allow the development of further innovative therapeutic strategies. In patients, the contribution of immune processes to the dysfunction in hereditary polyneuropathies and the association of hereditary neuropathy and CIDP has been described. Commonly used therapies remain corticosteroids, intravenous immunoglobulin and plasmapheresis; however, newer immunosuppressant approaches using mycophenolate mofetil or cyclosporin A, or immunomodulating therapies using monoclonal antibodies or interferons are presently under investigation. SummaryThe growing body of knowledge on the pathogenesis of CIDP and further diagnostic differentiation of subforms may help to develop more-effective therapies for CIDP in the next few years.

Time course of inwardly rectifying K+ current reduction in glial cells surrounding ischemic brain lesions

K(+) currents of activated glial cells surrounding ischemic infarcts are investigated using acutely dissociated cells from the periinfarct area after permanent middle cerebral artery occlusion in rats. Inwardly rectifying K(+) currents (K(IR)) were markedly reduced in cells neighboring infarcts with maximal alteration at day 3 after infarct followed by a partial recovery. This reduction of glial K(IR) currents may contribute to the functional disturbances in the periinfarct area.

Cyclic AMP and tumor necrosis factor-α regulate CXCR4 gene expression in Schwann cells

Rat peripheral nerve Schwann cells have been shown to express the alpha-chemokine receptor CXCR4 as well as the corresponding ligand stromal cell-derived factor-1 (SDF-1). We have investigated gene regulatory mechanisms acting on the expression of CXCR4 in cultured rat Schwann cells and found that receptor expression at transcript- and protein levels is directly dependent on intracellular cyclic AMP. Such increased levels of CXCR4 expression were found to be efficiently reversed by the action of tumor necrosis factor-alpha (TNFalpha). We also provide evidence that the POU box transcription factor Oct-6/SCIP is involved in the control of CXCR4 transcription. Finally, we could demonstrate that CXCR4 activation by SDF-1alpha increases the number of dying Schwann cells, indicating that this receptor/ligand interaction is modulating cell survival. Our data, therefore, suggest that in the Schwann cell lineage signal transduction cascades controlled by the activation of TNF- and CXCR4 receptors are functionally coupled.

TNFα reduces glutamate induced intracellular Ca2+ increase in cultured cortical astrocytes

Abstract The proinflammatory cytokine TNFα is locally released during various inflammatory CNS diseases and high cerebrospinal fluid (CSF) titers of TNFα were found in meningitis patients. We know from previous studies that TNFα also depolarizes astrocytes by reducing their inwardly rectifying K+ currents. We have now investigated the effect of TNFα on the glutamate induced intracellular Ca2+ increase in astrocytes, a process which seems to be involved in glial mediated modulation of neuronal synaptic transmisssion. Incubation with TNFα (50–1000 U/ml for 60 min) reduces the glutamate induced intracellular Ca2+ increase in astrocytes but not in neurons and this seems to be a phenomenon secondary to the TNFα induced depolarization. While other proinflammatory cytokines (interleukin 1β, IL-2, IL-6) did not interfere with the astrocytic glutamate response, incubation in CSF from septic meningitis patients (CSF–SM) also reduced the glutamate induced intracellular Ca2+ increase. The application of a neutralizing anti-TNFα antibody to the CSF–SM prior to cell incubation partially restored the glutamate response. Our data suggest that inflammatory molecules such as TNFα impair astrocytes’ response to glutamate and this may indirectly affect neuronal synaptic transmission.

HIV-1 protein Tat reduces the glutamate-induced intracellular Ca2+ increase in cultured cortical astrocytes

The trans‐activator protein Tat of the human immunodeficiency virus type 1 (HIV‐1) is regarded as an injurious molecule in the pathogenesis of HIV‐1 associated encephalopathy (HIVE). We investigated the effects of Tat on neuroligand‐induced intracellular Ca2+ increase in cultured astroglial cells. Rat cortical astrocytes, human glioblastoma cells and glial restricted precursor cells, from a human embryonic teratocarcinoma cell line, were incubated with recombinant Tat (100 ng/mL for 60 min) which induced a significant reduction of glutamate or ATP‐induced intracellular Ca2+ increase (‘glutamate response’, ‘ATP response’). The reduction of the glutamate response was also observed following cell incubation with cell extracts of HeLa‐T4+ cells transiently transfected with an expression plasmid coding for Tat. However, inactivation of the transcriptional trans‐activity of Tat, by using a mutant form of Tat, as well as inhibition of de novo protein synthesis by cycloheximide abolished the effect on the glutamate response. This suggests that Tat acts upon induction of a so far unknown cellular gene whoes gene product causes the reduction of glutamate responses. As the effect of Tat resembles the effect of TNFα on glutamate responses [Köller et al. (2001) Brain Res., 893, 237–243] which is locally released within the brains of HIVE patients, we also tested for synergistic effects of Tat and TNFα on the glutamate response. Low concentrations of Tat in combination with subthreshold concentrations of TNFα also elicited a marked reduction of astroglial glutamate responses. Our data suggest that Tat and TNFα, both by itself and synergistically, induce astroglial dysfunction.