Saikosaponin D Attenuates Postherpetic Neuralgia and Reduces Inflammation by Regulating Gut Microbiota in a Rodent...

Saikosaponin D (SSD) is a triterpenoid saponin derived from Bupleuri Radix and has therapeutic potential for the treatment of neuropathic pain. This study investigates the roles and underlying mechanisms of SSD in cellular and mouse models of resiniferatoxin (RTX)-induced postherpetic neuralgia (PHN). C57BL/6 mice were randomly assigned into four groups: control, RTX, RTX + vehicle, and RTX + SSD. Mechanical and thermal sensitivity were assessed to evaluate pain behaviors. Gut microbiota was depleted using antibiotic treatment, and fecal microbiota transplantation was used to restore gut flora in RTX-treated mice that received either vehicle or SSD. In vitro, RTX-stimulated human neuroblastoma SH-SY5Y cells were used as a cellular model of PHN. TRPA1 expression levels in mouse dorsal root ganglion and SH-SY5Y cells were measured by RT-qPCR and immunofluorescence staining. The levels of proinflammatory cytokines were evaluated in serum samples and SH-SY5Y cells via RT-qPCR or ELISA. Western blot was performed to assess protein levels of genes involved in TLR4/NF-κB and JAK/STAT3 pathways. Results showed that SSD attenuated RTX-induced neuralgia in mice. In both in vitro and in vivo models, SSD significantly reduced TRPA1 expression and proinflammatory cytokine levels. The protective effects of SSD against neuralgia were abolished following antibiotic-mediated gut microbiota depletion in mice. Fecal microbiota transplantation from SSD-treated mice alleviated RTX-induced neuralgia and inflammation in PHN model mice. Moreover, SSD reduced TLR4 protein level and reduced phosphorylation ratios of NF-κB p65, STAT3, and JAK in the lumbar spinal cord of RTX-treated mice and in SH-SY5Y cells. In conclusion, SSD alleviates RTX-induced PHN and inflammation in mice by modulating gut microbiota via the TLR4/NF-κB and JAK/STAT3 pathways.