Inhibition of Neuromyelitis Optica Immunoglobulin G Binding to Aquaporin-4 by the Small Molecule Blocker Melanthioidine

Background: Neuromyelitis optica (NMO) is a severe neurological demyelinating autoimmune disease affecting the optic nerves and spinal cord. The binding of neuromyelitis optica immunoglobulin G (NMO-IgG) and aquaporin-4 (AQP4) on the surface of astrocytes in the serum and cerebrospinal fluid is the main pathogenesis of NMO. Currently, therapeutic strategies for NMO include a reduction of the secondary inflammation response and the number of NMO-IgG, which can only alleviate clinical symptoms rather than fundamentally preventing a series of pathological processes caused by NMO-IgG binding to AQP4. Objective: The purpose of this study was to investigate the blocking effect of melanthioidine on the binding of NMO-IgG to AQP4 and its potential cytotoxicity. Methods: The current study developed a cell-based high-throughput screening approach to identify a molecular blocker of NMO-IgG binding to AQP4 using the Chinese hamster lung fibroblast (V79) cells expressing M23AQP4. By screening similar to 400 small molecules, we identified melanthioidine with blocking effects without affecting AQP4 expression or its water permeability. Results: Melanthioidine effectively blocked the binding of NMO-IgG to AQP4 in immunofluorescence assays and reduced complement-dependent cytotoxicity against both NMO-IgG/complement-treated Fischer rat thyroid-AQP4 cells and primary astrocytes. The docking computations identified the putative sites of blocker binding at the extracellular surface of AQP4. Conclusion: This study serves as proof of a potential NMO therapy by using a small-molecule blocker to target NMO pathogenesis.