Boldine inhibits SARM1 NADase Activity and Preserves Axonal Integrity After Nerve Injury

Wallerian degeneration of anucleated axonal segments is driven by SARM1, which depletes axonal NAD+, disrupting energy metabolism and triggering self-destruction. SARM1 inhibition is an emerging therapeutic target for traumatic nerve injuries. Boldine, a natural aporphine alkaloid from Peumus boldus, modulates connexin hemichannels, oxidative stress, and inflammation. Building on our published work showing boldines neuroprotective effects in nerve injury models, we hypothesized that boldine also inhibits SARM1 directly. A fluorescence polarization assay revealed that boldine inhibits SARM1 NADase activity with an IC50 of approximately 7.5 uM. AI-assisted structural modeling (AlphaFold3-based Boltz-1 with GNINA docking) predicted two boldine binding sites on SARM1: the TIR catalytic site (Kd [~] 13.5 uM) and the ARM-TIR regulatory interface (Kd [~] 12 uM). In a sciatic nerve explant model, boldine preserved the integrity of anucleated axonal segments at 3 and 7 days post-transection relative to vehicle controls. These findings suggest boldine may act as a dual-site SARM1 inhibitor and support its development as a neuroprotective therapy after traumatic axonal injury.