From the Palo Alto Veterans Institute for Research, Veterans Affairs Palo Alto Health Care System, Palo Alto, California.
Anesthesiology Service, Veterans Affairs Palo Alto Health Care System, Palo Alto, California.
Anesth Analg. 2021 May 1;132(5):1475-1485. doi: 10.1213/ANE.0000000000005440.
Complex regional pain syndrome (CRPS) is a highly disabling cause of pain often precipitated by surgery or trauma to a limb. Both innate and adaptive immunological changes contribute to this syndrome. Dimethyl fumarate (DMF) works through the nuclear factor erythroid 2-related factor 2 (Nrf2) transcription factor and other targets to activate antioxidant systems and to suppress immune system activation. We hypothesized that DMF would reduce nociceptive, functional, and immunological changes measured in a model of CRPS.
Male C57BL/6 mice were used in the well-characterized tibial fracture model of CRPS. Some groups of mice received DMF 25 mg/kg/d orally, per os for 3 weeks after fracture versus vehicle alone. Homozygous Nrf2 null mutant mice were used as test subjects to address the need for this transcription factor for DMF activity. Allodynia was assessed using von Frey filaments and hindlimb weight-bearing data were collected. The markers of oxidative stress malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) were quantified in the skin of the fractured mice using immunoassays along with the innate immune system cytokines IL-1β and IL-6. The accumulation of IgM in the fractured limbs and lymph node hypertrophy were used as indexes of adaptive immune system activation, and the passive transfer of serum from wildtype fractured mice to B cell-deficient fractured muMT mice (mice lacking B cells and immunoglobulin) helped to assess the pronociceptive activity of humoral factors.
We observed that oral DMF administration strongly prevented nociceptive sensitization and reduced uneven hindlimb weight bearing after fracture. DMF was also very effective in reducing the accumulation of markers of oxidative stress, activation of innate immune mediator production, lymph node hypertrophy, and the accumulation of IgM in fractured limbs. The sera of fractured vehicle-treated but not DMF-treated mice conferred pronociceptive activity to recipient mice. Unexpectedly, the effects of DMF were largely unchanged in the Nrf2 null mutant mice.
Oxidative stress and immune system activation are robust after hindlimb fracture in mice. DMF strongly reduces activation of those systems, and the Nrf2 transcription factor is not required. DMF or drugs working through similar mechanisms might provide effective therapy for CRPS or other conditions where oxidative stress causes immune system activation.
复杂性区域疼痛综合征（CRPS）是一种常见的致残性疾病，常由四肢手术或创伤引发。先天和适应性免疫变化均有助于该综合征的发生。二甲基富马酸（DMF）通过核因子红细胞 2 相关因子 2（Nrf2）转录因子和其他靶点发挥作用，激活抗氧化系统并抑制免疫系统激活。我们假设 DMF 可减轻 CRPS 模型中测量到的痛觉过敏、功能和免疫学变化。
雄性 C57BL/6 小鼠用于研究胫骨骨折 CRPS 模型。部分骨折后给予 DMF 25mg/kg/d 口服治疗，持续 3 周，而部分给予单纯溶剂。采用 Nrf2 纯合缺失突变小鼠作为研究对象，以确定该转录因子是否是 DMF 活性所必需的。采用免疫测定法测定骨折小鼠皮肤中丙二醛（MDA）和 4-羟基壬烯醛（4-HNE）等氧化应激标志物，同时测定固有免疫系统细胞因子 IL-1β和 IL-6。通过检测 IgM 在骨折肢体中的积累和淋巴结肿大情况，评估适应性免疫系统的激活情况，将野生型骨折小鼠的血清被动转移到缺乏 B 细胞的 muMT 骨折小鼠（缺乏 B 细胞和免疫球蛋白的小鼠）中，以评估体液因子的致痛活性。
我们发现，口服 DMF 给药可强烈预防骨折后痛觉过敏和下肢负重不均。DMF 还可非常有效地减少氧化应激标志物的积累、固有免疫介质产生的激活、淋巴结肿大和 IgM 在骨折肢体中的积累。与 DMF 治疗组不同，骨折后给予溶剂治疗的小鼠血清可赋予接受者小鼠致痛活性。出乎意料的是，Nrf2 缺失突变小鼠的 DMF 作用基本不变。
在小鼠下肢骨折后，氧化应激和免疫系统激活非常活跃。DMF 可强烈减少这些系统的激活，而 Nrf2 转录因子并非必需。DMF 或通过类似机制发挥作用的药物可能为 CRPS 或其他由氧化应激引起免疫系统激活的疾病提供有效的治疗方法。
