Characteristics and mechanisms of pain in sickle cell disease

描述(申请人提供)：镰状细胞病(SCD)伴有急性疼痛发作(“危象”)叠加慢性疼痛。阿片类药物是治疗严重疼痛的唯一方法，但治疗SCD疼痛需要大剂量的阿片类药物。长期使用阿片类药物可能会导致继发性不良反应和阿片类药物耐受。SCD慢性疼痛的潜在机制仍不清楚。确定SCD的疼痛特征并确定其潜在的机制是开发新的止痛疗法所必需的。因此，这项建议的目标是使用SCD的小鼠模型来检查在这种情况下导致疼痛的外周和脊髓机制。已建立的SCD小鼠模型具有独特的优势，因为它们与人类的遗传、血液和病理疾病相似。我们假设炎症、缺氧-再灌注损伤和“危象”持续激活伤害性感受器导致中枢敏感化。我们的初步数据表明，SCD小鼠表现出与SCD患者相似的皮肤(机械、热和冷)和深度(握力降低)痛敏。我们将采用多学科的方法，结合相关的行为学、电生理学和神经化学研究来检验以下假设：(1)镰刀鼠表现出皮肤和深度痛敏，这可以被外周大麻素调节。我们将通过测量对机械、热和冷刺激的撤退反应来检查皮肤疼痛，并通过测量握力来测量深度/肌肉骨骼疼痛。我们假设，足底注射大麻素受体激动剂可以减少皮肤痛敏，这是通过激活CB1和CB2受体实现的。(2)SCD伴有皮肤和脊髓周围神经纤维和炎症介质的激活。我们将检查外周和脊髓中促炎症细胞的激活，这些细胞导致神经元激活和敏化。(3)SCD疼痛涉及脊髓伤害性神经元的敏感化。我们将记录单个、已鉴定的宽动态范围和高阈值背角神经元在对照组和有痛觉过敏的SCD小鼠中的电生理反应。在拟议的研究中，我们将使用表达镰状血红蛋白的转基因杂合子Berk(HBERK)小鼠和表达正常人类血红蛋白的年龄和性别匹配的对照小鼠(HBA-BERK)。镰刀状hBERK小鼠具有混合遗传背景，并携带人类1和2S珠蛋白的单拷贝连锁转基因。它们对小鼠1珠蛋白的敲除是纯合的，对小鼠2珠蛋白的敲除是杂合的。HBA-Berk对照具有相同的遗传背景。我们预计镰状小鼠将表现出类似于SCD疼痛的疼痛特征，大麻类化合物激活CB1和C2受体将减轻痛敏，外周和中枢敏化有助于镰状小鼠疼痛。这些研究的结果将为SCD疼痛的潜在机制提供新的信息。了解SCD疼痛的基本机制将有助于开发治疗SCD疼痛的新的、更有效的方法。 公共卫生相关性：终生剧烈疼痛损害了SCD患者的生活质量。大剂量阿片类药物是唯一伴随着副作用的治疗方法。我们的目标是了解SCD中潜在的疼痛机制，以开发更有效和新的疗法来治疗SCD中的疼痛。如果我们的假设被证明是正确的，我们的结果将提供一个理解，这将有助于治疗SCD的疼痛和开发新的和更有效的止痛药。

DESCRIPTION (provided by applicant): Sickle cell disease (SCD) is accompanied by acute painful episodes ("crises") superimposed on chronic pain. Opioids are the only therapy for severe pain, but high doses of opioids are required to treat pain in SCD. Chronic opioid use may lead to secondary adverse effects and opioid tolerance. The mechanisms underlying chronic pain in SCD remain unknown. Characterizing pain in SCD and defining the underlying mechanisms is required to develop novel analgesic therapies. Therefore, the goal of this proposal is to use a murine model of SCD to examine peripheral and spinal mechanisms that contribute to pain in this condition. Established mouse models of SCD offer a unique advantage because of their similarity to human genetic, hematologic and pathological disease. We hypothesize that persistent activation of nociceptors by inflammation, hypoxia- reperfusion injury and "crises" leads to central sensitization. Our preliminary data indicate that mice with SCD exhibit cutaneous (mechanical, heat and cold) and deep (decreased grip force) hyperalgesia similar to that observed in patients with SCD. We will employ a multidisciplinary approach with correlative behavioral, electrophysiological and neurochemical studies to examine the following hypotheses: (1) sickle mice exhibit cutaneous and deep hyperalgesia, which can be modulated by peripheral cannabinoids. We will examine cutaneous pain by measuring withdrawal responses to mechanical, heat and cold stimuli and deep/musculoskeletal pain using measurement of grip force. We hypothesize that intraplantar administration of cannabinoid receptor agonists reduce cutaneous hyperalgesia and this occurs through activation of CB1 and CB2 receptors. (2) SCD is accompanied by activation of peripheral nerve fibers and inflammatory mediators of pain in the skin and spinal cord. We will examine the activation of pro-inflammatory cells in the periphery and spinal cord that lead to neuronal activation and sensitization. (3) Pain in SCD involves sensitization of nociceptive spinal neurons. We will record electrophysiological responses of single, identified wide dynamic range and high threshold dorsal horn neurons in control and in SCD mice with hyperalgesia. In the proposed studies, we will use transgenic heterozygous BERK (hBERK) mice expressing sickle hemoglobin and age and sex matched control mice expressing normal human hemoglobin (HbA-BERK). Sickle hBERK mice have a mixed genetic background and carry a single copy of linked transgenes for human 1 and 2S globins. They are homozygous for knockout of murine 1 globin and heterozygous for knockout of murine 2 globin. HbA-BERK controls have an identical genetic background. We expect that sickle mice will show pain characteristics similar to pain in SCD, that activation of CB1 and C2 receptors by cannabinoids will attenuate hyperalgesia and that peripheral and central sensitization contributes to pain in sickle mice. Results of these studies will provide new information on the mechanisms underlying pain in SCD. Understanding the basic mechanisms of pain in SCD will lead to the development of novel and more effective approaches to treat pain in SCD. PUBLIC HEALTH RELEVANCE: Lifelong severe pain impairs quality of life in patients with SCD. High doses of opioids are the only therapy accompanied by secondary side effects. Our goal is to develop an understanding of mechanisms underlying pain in SCD to develop more effective and novel therapies to treat pain in SCD. If our hypotheses prove to be true, our results will provide an understanding that will facilitate treating pain in SCD and in developing novel and more effective analgesics.