Supplementary Material for: Isotetrandrine Reduces Astrocyte Cytotoxicity in Neuromyelitis Optica by Blocking the Binding of NMO-IgG to Aquaporin 4

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 ∼3 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.