Tanshinone â…¡a Down-regulates HMGB1and TLR4Expression In A Spinal Nerve Ligation Model Of Neuropathic Pain

Objective:To assess the efficacy of intraperitoneal administration of Tanshinone IIA (Tan IIA) in a lumbar5(L5) spinal nerve ligation (SNL) neuropathic pain modelMethods:A total of54Sprague-Dawley rats weighing200～240g were randomly divided into three groups:a sham-operated group (sham group), a vehicle-treated SNL group (model group) and a Tan IIA-treated SNL group (Tan IIA group). Each group was divided into subgroups (n=6in each) according to the time of sacrifice:3days,7days and14days. Under general anaesthesia with chloral hydrate (300mg/kg, ip), the left L5spinal nerve distal to the dorsal root ganglion (DRG) was tightly ligated with6～0silk sutures and then snipped. Tan IIA was administered intraperitoneally to rats in the Tan IIA-treated group at a dose of30mg/kg daily for14days after surgery. Sham-operated rats received sterile water injections as a control. The same dose of sterile water was administered to rats in the vehicle-treated group. Paw withdrawal mechanical thresholds (PWTs) and paw withdrawal thermal latencies (PWLs) were measured1day before SNL (baseline) and3,7and14days after surgery. The L4～5lumbar segment of the spinal cord was removed to assay high-mobility group box1(HMGB1) and Toll-like Receptor4(TLR4) mRNA and protein expression by real-time quantitative PCR and western blotting, respectively. Tumour necrosis factor alpha (TNF-a), interleukin-1beta (IL-1β) and interleukin-10(IL-10) in the spinal cord were measured using an enzyme-linked immunosorbent assay (ELISA).Results:Both the mechanical and heat pain thresholds were significantly decreased (P<0.05versus sham group). HMGB1and TLR4mRNA and protein expression were at a low level in the sham group, and the levels began to increase at3days after SNL surgery and remained at a high level during the experiment (P<0.05versus sham group). After Tan IIA treatment, HMGB1and TLR4mRNA and protein levels were reduced significantly (P<0.05versus model group). TNF-α and IL-1β were up-regulated, but IL-10was down-regulated in the spinal cords of SNL-induced rats (P <0.05versus sham group). After Tan IIA treatment, the expression of TNF-α and IL-1β was reduced significantly (P<0.05versus model group). The IL-10level increased, which was accompanied by improvement of pain behaviours in the Tan IIA group (P<0.05). Conclusion:Tanshinone IIA reversed SNL-induced thermal hyperalgesia and mechanical allodynia. Tanshinone IIA down-regulated HMGB1and TLR4levels and inhibited the HMGB1-TLR4pathway. Tanshinone IIA inhibited TNF-α and IL-1β expression but not IL-10expression in the spinal cords of SNL rats. These results indicate Tanshinone IIA inhibited SNL-induced neuropathic pain via multiple effects, and targeting the HMGB1-TLR4pathway could serve as the basis of new anti-nociceptive agents.