Jop P. Mostert

Dysfunctional astrocytes as key players in the pathogenesis of central nervous system disorders

Once considered little more than the glue that holds neurons in place, astrocytes are now becoming appreciated for the key roles they play in central nervous system functions. They supply neurons and oligodendrocytes with substrates for energy metabolism, control extracellular water and electrolyte homeostasis, regulate neurotransmitter release, modulate immune responses, produce trophic factors, and control synapse formation. Astrocytes express receptors for many neurotransmitters, peptides, hormones and cytokines, and show excitability based on intracellular Ca2+ variations. Evidence is mounting that alterations in astrocyte functionality play a crucial role in the pathogenesis of disorders with diverse properties, including migraine, epilepsy, leukodystrophies, inflammatory demyelinating diseases, infections, brain edema and metabolic disorders, metal intoxications, neurodegenerative disorders, and schizophrenia. Targeting astrocyte dysfunction may lead to new therapeutic strategies for these disorders.

Tremor in multiple sclerosis

Tremor is estimated to occur in about 25 to 60 percent of patients with multiple sclerosis (MS). This symptom, which can be severely disabling and embarrassing for patients, is difficult to manage. Isoniazid in high doses, carbamazepine, propranolol and gluthetimide have been reported to provide some relief, but published evidence of effectiveness is very limited. Most trials were of small size and of short duration. Cannabinoids appear ineffective. Tremor reduction can be obtained with stereotactic thalamotomy or thalamic stimulation. However, the studies were small and information on long-term functional outcome is scarce. Physiotherapy, tremor reducing orthoses, and limb cooling can achieve some functional improvement. Tremor in MS remains a significant challenge and unmet need, requiring further basic and clinical research.

Hypoperfusion of the cerebral white matter in multiple sclerosis: possible mechanisms and pathophysiological significance.

Multiple sclerosis (MS) is a disease of the central nervous system characterized by patchy areas of demyelination, inflammation, axonal loss and gliosis, and a diffuse axonal degeneration throughout the so-called normal-appearing white matter (NAWM). A number of recent studies using perfusion magnetic resonance imaging in both relapsing and progressive forms of MS have shown a decreased perfusion of the NAWM, which does not appear to be secondary to axonal loss. The reduced perfusion of the NAWM in MS might be caused by a widespread astrocyte dysfunction, possibly related to a deficiency in astrocytic β2-adrenergic receptors and a reduced formation of cAMP, resulting in a reduced uptake of K+ at the nodes of Ranvier and a reduced release of K+ in the perivascular spaces. Pathologic and imaging studies suggest that ischemic changes might be involved in the development of a subtype of focal demyelinating lesions (type III lesions), and there appears to exist a relationship between decreased white matter perfusion and cognitive dysfunction in patients with MS.

Therapeutic Potential of Fluoxetine in Neurological Disorders

The selective serotonin reuptake inhibitor (SSRI) fluoxetine, which is registered for a variety of psychiatric disorders, has been found to stimulate the cAMP‐responsive element binding protein (CREB), increase the production of brain‐derived neurotrophic factor (BNDF) and the neurotrophic peptide S100β, enhance glycogenolysis in astrocytes, block voltage‐gated calcium and sodium channels, and decrease the conductance of mitochondrial voltage‐dependent anion channels (VDACs). These mechanisms of actions suggest that fluoxetine may also have potential for the treatment of a number of neurological disorders. We performed a Pubmed search to review what is known about possible therapeutic effects of fluoxetine in animal models and patients with neurological disorders. Beneficial effects of fluoxetine have been noted in animal models of stroke, multiple sclerosis, and epilepsy. Fluoxetine was reported to improve neurological manifestations in patients with Alzheimers disease, stroke, Huntingtons disease, multiple sclerosis, traumatic brain injury, and epilepsy. Clinical studies so far were small and often poorly designed. Results were inconclusive and contradictory. However, the available preclinical data justify further clinical trials to determine the therapeutic potential of fluoxetine in neurological disorders.

Effects of fluoxetine on disease activity in relapsing multiple sclerosis: a double-blind, placebo-controlled, exploratory study

Background: Suppressing the antigen-presenting capacity of glial cells could represent a novel way of reducing inflammatory activity in multiple sclerosis (MS). Aims: To evaluate the effects of fluoxetine on new lesion formation in patients with relapsing MS. Methods: In a double-blind, placebo-controlled exploratory study, 40 non-depressed patients with relapsing remitting or relapsing secondary progressive MS were randomised to oral fluoxetine 20 mg or placebo daily for 24 weeks. New lesion formation was studied by assessing the cumulative number of gadolinium-enhancing lesions on brain MRI performed on weeks 4, 8, 16 and 24. Results: Nineteen patients in both groups completed the study. The mean (SD) cumulative number of new enhancing lesions during the 24 weeks of treatment was 1.84 (2.9) in the fluoxetine group and 5.16 (8.6) in the placebo group (p = 0.15). The number of scans showing new enhancing lesions was 25% in the fluoxetine group versus 41% in the placebo group (p = 0.04). Restricting the analysis to the past 16 weeks of treatment showed that the cumulative number of new enhancing lesions was 1.21 (2.6) in the fluoxetine group and 3.16 (5.3) in the placebo group (p = 0.05). The number of patients without enhancing lesions was 63% in the fluoxetine group versus 26% in the placebo group (p = 0.02). Conclusions: This proof-of-concept study shows that fluoxetine tends to reduce the formation of new enhancing lesions in patients with MS. Further studies with this compound are warranted. Trial registration: Number: ISRCTN65586975

Progression in multiple sclerosis: Further evidence of an age dependent process

The relapsing-remitting phase and the progressive phase of multiple sclerosis (MS) seem to be the result of distinct pathophysiological processes. Previous research on the natural history of MS was largely focussed on relapses and disability scores. In this study we evaluated 438 patients with secondary or primary progressive MS. The influence of gender, initial disease course, onset manifestation and age at disease onset on age at progression and time to progression were evaluated with Kaplan-Meier survival analysis and Cox multivariate regression models. The analysis of these data showed that the initial disease course (SPMS or PPMS) had no influence on the age at progression. Gender had no influence on age at progression in PPMS and SPMS patients nor on time to progression in SPMS patients. PPMS patients with visual or brainstem/cerebellar onset had a significantly younger age at progression. SPMS patients with motor onset had a significantly higher age at progression and longer time to progression. Time to progression was significantly shorter in SPMS patients with higher age at disease onset. Our data give further support to the notion that progression in MS is an age dependent process independent of relapses.

Plasma lipid peroxidation and progression of disability in multiple sclerosis

Oxidative stress has been implicated in the pathophysiology of multiple sclerosis (MS), but its relation to disease progression is uncertain. To evaluate the relationship of plasma lipid peroxidation with progression of disability in MS, we measured blood plasma fluorescent lipid peroxidation products (PFLPP) levels in 23 patients with RRMS with a benign course, 32 with secondary progressive MS, 24 with primary progressive MS and 30 healthy controls. None of the patients had a relapse within the previous 3 months. Progression of disability was evaluated during a follow‐up period of 5 years by the Expanded Disability Status Scale (EDSS) and the Multiple Sclerosis Severity Score (MSSS). We found plasma PFLPP levels elevated in patients with MS compared with controls (P < 0.0001), but there was no difference between patients with a benign and progressive disease course. There was no correlation between PFLPP levels and worsening of disability on the EDSS and speed of progression on the MSSS. Our data suggest that there is no relation between the degree of oxidative stress in plasma and progression of disability in MS.

A randomized crossover study of bee sting therapy for multiple sclerosis

Background: Bee sting therapy is increasingly used to treat patients with multiple sclerosis (MS) in the belief that it can stabilize or ameliorate the disease. However, there are no clinical studies to justify its use. Methods: In a randomized, crossover study, we assigned 26 patients with relapsing-remitting or relapsing secondary progressive MS to 24 weeks of medically supervised bee sting therapy or 24 weeks of no treatment. Live bees (up to a maximum of 20) were used to administer bee venom three times per week. The primary outcome was the cumulative number of new gadolinium-enhancing lesions on T1-weighted MRI of the brain. Secondary outcomes were lesion load on T2*-weighted MRI, relapse rate, disability (Expanded Disability Status Scale, Multiple Sclerosis Functional Composite, Guy’s Neurologic Disability Scale), fatigue (Abbreviated Fatigue Questionnaire, Fatigue Impact Scale), and health-related quality of life (Medical Outcomes Study 36-Item Short Form General Health Survey). Results: During bee sting therapy, there was no significant reduction in the cumulative number of new gadolinium-enhancing lesions. The T2*-weighted lesion load further progressed, and there was no significant reduction in relapse rate. There was no improvement of disability, fatigue, and quality of life. Bee sting therapy was well tolerated, and there were no serious adverse events. Conclusions: In this trial, treatment with bee venom in patients with relapsing multiple sclerosis did not reduce disease activity, disability, or fatigue and did not improve quality of life.

Impact of fluoxetine on the human brain in multiple sclerosis as quantified by proton magnetic resonance spectroscopy and diffusion tensor imaging

The antidepressant fluoxetine stimulates astrocytic glycogenolysis, which serves as an energy source for axons. In multiple sclerosis patients fluoxetine administration may improve energy supply in neuron cells and thus inhibit axonal degeneration. In a preliminary pilot study, 15 patients with multiple sclerosis (MS) were examined by diffusion tensor imaging (DTI) and (1)H magnetic resonance spectroscopy (MRS) in order to quantify the brain tissue diffusion properties (fractional anisotropy, apparent diffusion coefficient) and metabolite levels (choline, creatine and N-acetylaspartate) in cortical gray matter brain tissue, in normal appearing white matter and in white matter lesions. After oral administration of fluoxetine (20 mg/day) for 1 week, the DTI and MRS measurements were repeated and after treatment with a higher dose (40 mg/day) during the next week, a third series of DTI/MRS examinations was performed in order to assess any changes in diffusion properties and metabolism. One trend was observed in gray matter tissue, a decrease of choline measured at weeks 1 and 2 (significant in a subgroup of 11 relapsing remitting/secondary progressive MS patients). In white matter lesions, the apparent diffusion coefficient was increased at week 1 and N-acetylaspartate was increased at week 2 (both significant). These preliminary results provide evidence of a neuroprotective effect of fluoxetine in MS by the observed partial normalization of the structure-related MRS parameter N-acetylaspartate in white matter lesions.

Astrocytes as potential targets to suppress inflammatory demyelinating lesions in multiple sclerosis

A hallmark of multiple sclerosis (MS) is the occurrence of focal inflammatory demyelinating lesions in the central nervous system. The prevailing view that activated anti-myelin T cells inherently mediate these lesions has been challenged after observations that these T cells, which are part of the normal immune repertoire, can also intermittently become activated in healthy people and subjects with other diseases. Astrocytes in the white matter of subjects with MS are deficient in beta(2) adrenergic receptors. Stimulation of beta(2) adrenergic receptors increases cAMP, leading to activation of protein kinase A (PKA). beta(2) adrenergic receptor deficiency will reduce the suppressive action of PKA on coactivator class II transactivator (CIITA), which is a key regulator of interferon gamma-induced major histocompatibility (MHC) class II molecule transcription. The expression of MHC class II may deviate astrocytes to function as facultative antigen presenting cells, which can then initiate the inflammatory cascade. In a proof of concept study in MS subjects it was shown that fluoxetine, which activates PKA in astrocytes, reduced the development of focal inflammatory lesions. If confirmed and extended by additional studies, suppressing the antigen presenting capacity of astrocytes could be a novel therapeutic option for the treatment of MS.