Botulinum toxin type E alleviates trigeminal neuropathic pain via modulation of the HIF-1α-NLRP3 pathway

While botulinum neurotoxin type E (BoNT/E) has been shown to have analgesic effects in previous studies, the underlying mechanisms mediating its therapeutic effects remain incompletely understood. This study investigated the involvement of the nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain-containing protein 3 (NLRP3) inflammasome in the antinociceptive effects of BoNT/E in a rat model of trigeminal neuropathic pain.

Neuropathic pain was induced in male Sprague-Dawley rats through inferior alveolar nerve (IAN) injury.

IAN injury significantly decreased air-puff thresholds, resulting in mechanical allodynia that persisted for up to 42 days. NLRP3 expression in the ipsilateral trigeminal ganglion (iTG) was significantly increased in the nerve-injured group on postoperative day (POD) 5. In contrast, subcutaneous administration of BoNT/E (6 or 10 U/kg) significantly attenuated mechanical allodynia and suppressed NLRP3 expression in the iTG on POD 5. Moreover, BoNT/E (10 U/kg) markedly reduced the elevated levels of inflammatory cytokines, including interleukin (IL)-1β, IL-18, tumor necrosis factor-alpha (TNF-α), and IL-6 in the iTG by IAN injury. The nerve-injured group also exhibited significant upregulation of hypoxia-inducible factor 1-alpha (HIF-1α) expression in the iTG, which was significantly decreased following BoNT/E (10 U/kg) treatment. Intraganglionic injection of PX-478, a HIF-1α inhibitor, similarly attenuated mechanical allodynia, downregulated NLRP3 expression, and decreased IL-1β, IL-18, TNF-α, and IL-6 levels in the iTG.

Collectively, these findings demonstrate that modulation of the HIF-1α-NLRP3 pathway in the iTG plays a critical regulatory role in neuropathic pain development and suggest that BoNT/E may serve as a promising therapeutic strategy for managing chronic neuropathic pain.