ABSTRACT
OBJECTIVE: Neuromyelitis optica (NMO) is a severe neurological demyelinating autoimmune disease that affects the optic nerves and spinal cord with no cure and no FDA-approved therapy. Research over the last decade revealed that the binding of NMO-IgG to the water channel protein astrocyte aquaporin 4 (AQP4) might be the primary cause of NMO pathogenesis. The purpose of this study was to identify potential blockers of NMO-IgG and AQP4 binding. METHODS: We developed a two-step screening platform consisting of a reporter cell-based high-throughput screen assay and a cell viability-based assay. Purified NMO-IgG from NMO patient serum and transfected Chinese hamster lung fibroblast V79 cells stably expressing human M23-AQP4 were used for primary screening of 40,000 small molecule fractions from 500 traditional Chinese herbs. RESULTS: Thirty-six positive fractions were identified, of which 3 active fractions (at 50 µg/ml) were found to be from the same Chinese traditional herb Mahonia japonica (Thunb.). A bioactivity-guided method based on a primary screening assay for blocking activity led to the isolation of an active single natural compound, isotetrandrine, from the 3 fractions. Our immunofluorescence staining results showed that isotetrandrine can block NMO-IgG binding to AQP4 without affecting the expression and function of AQP4. It can also inhibit NMO-IgG binding to astrocyte AQP4 in NMO patient sera and block NMO-IgG-dependent complement-mediated cytotoxicity with the IC50 at â¼3 µM. CONCLUSIONS: The present study developed a cell-based high-throughput screen to identify small molecule inhibitors for NMO-IgG and AQP4 binding, and suggests a potential therapeutic value of isotetrandrine in NMO.
Subject(s)
Aquaporin 4/metabolism , Astrocytes/metabolism , Benzylisoquinolines/pharmacology , Drugs, Chinese Herbal/pharmacology , Immunoglobulin G/metabolism , Neuromyelitis Optica/metabolism , Animals , Aquaporin 4/antagonists & inhibitors , Astrocytes/drug effects , Astrocytes/pathology , Benzylisoquinolines/therapeutic use , CHO Cells , Cells, Cultured , Cricetinae , Cricetulus , Drug Evaluation, Preclinical/methods , Drugs, Chinese Herbal/therapeutic use , Humans , Immunosuppressive Agents/pharmacology , Immunosuppressive Agents/therapeutic use , Mice , Mice, Knockout , Neuromyelitis Optica/drug therapy , Neuromyelitis Optica/pathology , Protein Binding/drug effects , Protein Binding/physiologyABSTRACT
Narcolepsy is a chronic sleep disorder, characterized by excessive daytime sleepiness (EDS), cataplexy, sleep paralysis and hypnagogic hallucinations. Both sporadic (95%) and familial (5%) forms of narcolepsy exist in humans. The major pathophysiology of human narcolepsy has been recently discovered based on the discovery of narcolepsy genes in animals; the genes involved in the pathology of the hypocretin/orexin ligand and its receptor. Mutations in hypocretin-related genes are rare in humans, but hypocretin ligand deficiency is found in a large majority of narcolepsy with cataplexy. Hypocretin ligand deficiency in human narcolepsy is probably due to the post-natal cell death of hypocretin neurones. Although a close association between human leucocyte antigen (HLA) and human narcolepsy with cataplexy suggests an involvement of autoimmune mechanisms, this has not yet been proved. Hypocretin deficiency is also found in symptomatic cases of narcolepsy and EDS with various neurological conditions, including immune-mediated neurological disorders, such as Guillain-Barre syndrome, MA2-positive paraneoplastic syndrome and neuromyelitis optica (NMO)-related disorder. The findings in symptomatic narcoleptic cases may have significant clinical relevance to the understanding of the mechanisms of hypocretin cell death and choice of treatment option. The discoveries in human cases lead to the establishment of the new diagnostic test of narcolepsy (i.e. low cerebrospinal fluid hypocretin-1 levels for 'narcolepsy with cataplexy' and 'narcolepsy due to medical condition'). As a large majority of human narcolepsy patients are ligand deficient, hypocretin replacement therapy may be a promising new therapeutic option, and animal experiments using gene therapy and cell transplantations are in progress.
Subject(s)
Intracellular Signaling Peptides and Proteins/metabolism , Narcolepsy/etiology , Narcolepsy/physiopathology , Neuropeptides/metabolism , Neurotransmitter Agents/metabolism , Animals , Cell Death , Circadian Rhythm , Humans , Hypothalamus/pathology , Intracellular Signaling Peptides and Proteins/deficiency , Ligands , Narcolepsy/therapy , Neuromyelitis Optica/metabolism , Neuromyelitis Optica/pathology , Neurons , Neuropeptides/deficiency , Orexins , Polymorphism, Genetic , Sleep Stages/physiologyABSTRACT
BACKGROUND: Neuromyelitis optica (NMO)-IgG is a specific autoantibody marker for NMO. It binds selectively to aquaporin 4 (AQP4), which is highly concentrated in astrocytic foot processes at the blood-brain barrier and is not restricted to optic nerve and spinal cord. Although it is conventionally believed that the brain is spared, brain imaging abnormalities are not uncommon in patients with NMO. OBJECTIVE: To investigate the location of brain lesions that are distinctive for NMO with respect to the localization of AQP4 in mammalian brain. DESIGN: Observational, retrospective case series. SETTING: Clinical serologic cohort of patients tested for NMO-IgG for whom brain MRI images were available. PATIENTS: We identified 120 patients seropositive for NMO-IgG for whom brain magnetic resonance images were available. MAIN OUTCOME MEASURE: Magnetic resonance imaging abnormalities. RESULTS: In 8 patients we observed recurring and distinctive magnetic resonance imaging abnormalities in the hypothalamic and periventricular areas that corresponded to brain regions of high AQP4 expression. CONCLUSION: The distribution of NMO-characteristic brain lesions corresponds to sites of high AQP4 expression.