Department of Medical Science, Chungnam National University School of Medicine, Daejeon 35015, Korea.
Department of Anesthesiology and Pain Medicine, Chungnam National University Hospital, Daejeon 35015, Korea.
Int J Mol Sci. 2019 Sep 9;20(18):4443. doi: 10.3390/ijms20184443.
Upon peripheral nerve injury, vesicular ATP is released from damaged primary afferent neurons. This extracellular ATP subsequently activates purinergic receptors of the spinal cord, which play a critical role in neuropathic pain. As an inhibitor of the vesicular nucleotide transporter (VNUT), Evans blue (EB) inhibits the vesicular storage and release of ATP in neurons. Thus, we tested whether EB could attenuate neuropathic pain behavior induced by spinal nerve ligation (SNL) in rats by targeting VNUT. An intrathecal injection of EB efficiently attenuated mechanical allodynia for five days in a dose-dependent manner and enhanced locomotive activity in an SNL rat model. Immunohistochemical analysis showed that EB was found in VNUT immunoreactivity on neurons in the dorsal root ganglion and the spinal dorsal horn. The level of ATP in cerebrospinal fluid in rats with SNL-induced neuropathic pain decreased upon administration of EB. Interestingly, EB blocked ATP release from neurons, but not glial cells in vitro. Eventually, the loss of ATP decreased microglial activity in the ipsilateral dorsal horn of the spinal cord, followed by a reduction in reactive oxygen species and proinflammatory mediators, such as interleukin (IL)-1β and IL-6. Finally, a similar analgesic effect of EB was demonstrated in rats with monoiodoacetate-induced osteoarthritis (OA) pain. Taken together, these data demonstrate that EB prevents ATP release in the spinal dorsal horn and reduces the ATP/purinergic receptor-induced activation of spinal microglia followed by a decline in algogenic substances, thereby relieving neuropathic pain in rats with SNL.
在外周神经损伤时,损伤的初级传入神经元从囊泡中释放出 ATP。这种细胞外的 ATP 随后激活脊髓中的嘌呤能受体,在神经病理性疼痛中发挥关键作用。作为囊泡核苷酸转运蛋白(VNUT)的抑制剂, Evans 蓝(EB)抑制神经元中 ATP 的囊泡储存和释放。因此,我们通过靶向 VNUT 测试了 EB 是否可以通过抑制 VNUT 来减轻脊神经结扎(SNL)诱导的大鼠神经病理性疼痛行为。鞘内注射 EB 能够以剂量依赖的方式有效减轻机械性痛觉过敏五天,并增强 SNL 大鼠模型的运动活性。免疫组织化学分析显示,EB 存在于背根神经节和脊髓背角神经元的 VNUT 免疫反应性中。SNL 诱导的神经病理性疼痛大鼠脑脊液中 ATP 水平在给予 EB 后降低。有趣的是,EB 阻断了神经元而非神经胶质细胞中 ATP 的释放。最终,同侧脊髓背角中小胶质细胞的 ATP 减少,随后活性氧和促炎介质(如白细胞介素 1β 和白细胞介素 6)减少。最后,在单碘乙酸诱导的骨关节炎(OA)疼痛大鼠中也证明了 EB 的类似镇痛作用。总之,这些数据表明,EB 可防止脊髓背角中 ATP 的释放,并减少 ATP/嘌呤能受体诱导的脊髓小胶质细胞的激活,随后降低致痛物质,从而缓解 SNL 大鼠的神经病理性疼痛。
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