Department of Anatomy, Institute of Medicine, Chung Shan Medical University, Taichung 40201, Taiwan; Department of Medical Education, Chung Shan Medical University Hospital, Taichung 40201, Taiwan.
Department of Anatomy, College of Medicine, China Medical University, Taichung 40402, Taiwan.
Neurotoxicology. 2019 Mar;71:60-74. doi: 10.1016/j.neuro.2018.12.006. Epub 2018 Dec 21.
Peripheral neuropathy, a chronic complication of diabetes mellitus (DM), is often accompanied by the onset of severe pain symptoms that affect quality of life. However, the underlying mechanisms remain elusive. In the present study, we used Sprague-Dawley rats to establish a rodent model of the human type 1 DM by a single intraperitoneal (i.p.) injection with streptozotocin (STZ) (60 mg/kg). Hypersensitivity, including hyperalgesia and allodynia, developed in the STZ-induced diabetic rats. Cutaneous innervation exhibited STZ-induced reductions of protein gene product 9.5-, peripherin-, and neurofilament 200-immunoreactivity (IR) subepidermal nerve fibers (SENFs). Moreover, the decreases of substance P (SP)- and calcitonin gene-related peptide (CGRP)-IR SENFs were distinct gathered from the results of extracellular signal-regulated kinase 1 and 2 (ERK1/2)- and phosphorylated ERK1/2 (pERK1/2)-IR SENFs in STZ-induced diabetic rats. Double immunofluorescence studies demonstrated that STZ-induced pERK1/2-IR was largely increased in SENFs where only a small portion was colocalized with SP- or CGRP-IR. By an intraplantar (i. pl.) injection with a MEK inhibitor, U0126 (1,4-Diamino-2,3-dicyano-1,4-bis[2-aminophenylthio]butadiene), hyperalgesia was attenuated in a dose-responsive manner. Botulinum toxin serotype A had dose-dependent analgesic effects on STZ-induced hyperalgesia and allodynia, which exhibited equivalent results as the efficacy of transient receptor potential vanilloid (TRPV) channel antagonists. Morphological evidence further confirmed that STZ-induced SP-, CGRP- and pERK1/2-IR were reduced in SENFs after pharmacological interventions. From the results obtained in this study, it is suggested that increases of pERK1/2 in SENFs may participate in the modulation of TRPV channel-mediated neurogenic inflammation that triggers hyperalgesia in STZ-induced diabetic rats. Therefore, ERK1/2 provides a potential therapeutic target and efficient pharmacological strategies to address hyperglycemia-induced neurotoxicity.
周围神经病变是糖尿病（DM）的一种慢性并发症，常伴有严重疼痛症状，影响生活质量。然而，其潜在机制仍不清楚。在本研究中，我们使用 Sprague-Dawley 大鼠通过单次腹腔内（i.p.）注射链脲佐菌素（STZ）（60mg/kg）建立了人类 1 型 DM 的啮齿动物模型。STZ 诱导的糖尿病大鼠出现过敏反应，包括痛觉过敏和感觉异常。表皮下神经纤维（SENFs）的蛋白基因产物 9.5、周围蛋白和神经丝 200-免疫反应性（IR）显示 STZ 诱导的减少。此外，与 STZ 诱导的糖尿病大鼠的细胞外信号调节激酶 1 和 2（ERK1/2）-和磷酸化 ERK1/2（pERK1/2）-IR SENFs 的结果相比，P 物质（SP）和降钙素基因相关肽（CGRP）-IR SENFs 的减少更为明显。双重免疫荧光研究表明，STZ 诱导的 pERK1/2-IR 在 SENFs 中大量增加，而 SP 或 CGRP-IR 仅在一小部分中存在共定位。通过足底（i.pl.）注射 MEK 抑制剂 U0126（1,4-二氨基-2,3-二氰基-1,4-双[2-氨基苯基硫]丁二烯），痛觉过敏以剂量反应的方式减弱。肉毒杆菌毒素 A 型对 STZ 诱导的痛觉过敏和感觉异常具有剂量依赖性的镇痛作用，其效果与瞬时受体电位香草酸（TRPV）通道拮抗剂相当。形态学证据进一步证实，药物干预后，SENFs 中的 STZ 诱导的 SP、CGRP 和 pERK1/2-IR 减少。从本研究结果中可以看出，SENFs 中 pERK1/2 的增加可能参与 TRPV 通道介导的神经源性炎症的调节，从而引发 STZ 诱导的糖尿病大鼠痛觉过敏。因此，ERK1/2 为解决高血糖引起的神经毒性提供了一个潜在的治疗靶点和有效的药物策略。
