Artemisinin (ART) was initially described for the control of inflammation and pain. However, the mechanisms involved with its antinociceptive effect are still poorly understood. Thus, this present study aimed to investigate the effect of ART in both free and nanocapsulated form on postoperative pain, as well as the participation of the spinal Toll-like receptor 4 (TLR4) in this process. Postoperative pain was induced using the skin/muscle incision retraction (SMIR) model in male Swiss mice. After 3 and 28 days of SMIR, the animals received an intrathecal injection of free or nanocapsulated ART, and the nociceptive threshold was evaluated by von Frey filament test. To evaluate the involvement of the microglia, astrocytes, and TLR4, minocycline (a microglia inhibitor), fluorocitrate (an astrocyte inhibitor), and Lipopolysaccharide Rhodobacter sphaeroides (LPS-RS), a TLR4 antagonist, were intrathecally injected on the third day of SMIR. The levels of spinal TLR4 protein and proinflammatory cytokines tumor necrosis factor-alpha (TNF-α), and interleukin-1-beta (IL-1β) were quantified by western blot and enzyme-linked immunosorbent assay, respectively. The results showed that free ART reduced postoperative pain (P < 0.001, F_5,30 = 7.49, 16.66% for 1000 ng dose; and P < 0.01, F_5,30 = 7.49, 14.58% for 500 ng dose) on the 3rd day of SMIR; while the ART nanocapsule had this effect on both the third (P < 0.001; F_5,30 = 4.94; 43.75, 39.58 and 72.91% for the 250, 500 and 1000 ng doses, respectively) and 28th (P < 0.05; F_5,30 = 7.71; 29.16 and 33.33% for the 500 and 1000 ng doses, respectively) day. The ART nanocapsule had a more potent and longer antinociceptive effect than free ART or morphine. Postoperative pain was also reduced by minocycline and LPS-RS. The ART nanocapsule also reduced the increased levels of TLR4, TNF-α, and IL-1β induced by SMIR. These data suggest that the ART nanocapsule has a potent analgesic effect on postoperative pain at the spinal level, and this response involves the inhibition of TLR4 and the proinflammatory cytokines TNF-α and IL-1β.

青蒿素（ART）最初用于控制炎症和疼痛。但是，有关其抗伤害感受作用的机制仍知之甚少。因此，本研究旨在研究游离和纳米囊形式的ART对术后疼痛以及脊髓Toll样受体4（TLR4）参与该过程的作用。使用雄性瑞士小鼠的皮肤/肌肉切口回缩（SMIR）模型诱发术后疼痛。SMIR 3天和28天后，对动物进行鞘内注射游离或纳米囊封的ART，并通过von Frey细丝试验评估其伤害阈值。为了评估小胶质细胞，星形胶质细胞和TLR4的参与，米诺环素（小胶质细胞抑制剂），氟柠檬酸盐（星形胶质细胞抑制剂）和在SMIR的第三天鞘内注射脂多糖球形红球菌（LPS-RS），一种TLR4拮抗剂。分别通过蛋白质印迹法和酶联免疫吸附法定量测定脊髓TLR4蛋白和促炎细胞因子肿瘤坏死因子-α（TNF-α）和白介素-1-β（IL-1β）的水平。结果表明，游离ART减少术后疼痛（P  <0.001，˚F _5,30  = 7.49，16.66％1000纳克的剂量;和P  <0.01，˚F _5,30  = 7.49，14.58为500ng的剂量％）3号SMIR日；而ART纳米胶囊对第三种均具有这种作用（P  <0.001; F _5,30 = 4.94; 第250、500和1000 ng剂量分别为43.75、39.58和72.91％）和第28天（分别为500和1000 ng剂量，P  <0.05；F _5,30  = 7.71； 29.16和33.33％）。ART纳米胶囊比游离ART或吗啡具有更强效和更长的镇痛作用。米诺环素和LPS-RS也减轻了术后疼痛。ART纳米胶囊还降低了SMIR诱导的TLR4，TNF-α和IL-1β的升高水平。这些数据表明，ART纳米胶囊在脊柱水平上对术后疼痛具有有效的镇痛作用，并且这种反应涉及对TLR4以及促炎细胞因子TNF-α和IL-1β的抑制。