Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN 47405-2204, United States.
Pharmacol Res. 2013 Jan;67(1):94-109. doi: 10.1016/j.phrs.2012.10.013. Epub 2012 Nov 2.
Cisplatin, a platinum-derived chemotherapeutic agent, produces mechanical and coldallodynia reminiscent of chemotherapy-induced neuropathy in humans. The endocannabinoid system represents a novel target for analgesic drug development. The endocannabinoid signaling system consists of endocannabinoids (e.g. anandamide (AEA) and 2-arachidonoylglycerol (2-AG)), cannabinoid receptors (e.g. CB(1) and CB(2)) and the enzymes controlling endocannabinoid synthesis and degradation. AEA is hydrolyzed by fatty-acid amide hydrolase (FAAH) whereas 2-AG is hydrolyzed primarily by monoacylglycerol lipase (MGL). We compared effects of brain permeant (URB597) and impermeant (URB937) inhibitors of FAAH with an irreversible inhibitor of MGL (JZL184) on cisplatin-evoked behavioral hypersensitivities. Endocannabinoid modulators were compared with agents used clinically to treat neuropathy (i.e. the opioid analgesic morphine, the anticonvulsant gabapentin and the tricyclic antidepressant amitriptyline). Cisplatin produced robust mechanical and cold allodynia but did not alter responsiveness to heat. After neuropathy was fully established, groups received acute intraperitoneal (i.p.) injections of vehicle, amitriptyline (30 mg/kg), gabapentin (100 mg/kg), morphine (6 mg/kg), URB597 (0.1 or 1 mg/kg), URB937 (0.1 or 1 mg/kg) or JZL184 (1, 3 or 8 mg/kg). Pharmacological specificity was assessed by coadministering each endocannabinoid modulator with either a CB(1) (AM251 3 mg/kg), CB(2) (AM630 3 mg/kg), TRPV1 (AMG9810 3 mg/kg) or TRPA1 (HC030031 8 mg/kg) antagonist. Effects of cisplatin on endocannabinoid levels and transcription of receptors (CB(1), CB(2), TRPV1, TRPA1) and enzymes (FAAH, MGL) linked to the endocannabinoid system were also assessed. URB597, URB937, JZL184 and morphine reversed cisplatin-evoked mechanical and cold allodynia to pre-cisplatin levels. By contrast, gabapentin only partially reversed the observed allodynia while amitriptyline, administered acutely, was ineffective. CB(1) or CB(2) antagonists completely blocked the anti-allodynic effects of both FAAH (URB597, URB937) and MGL (JZL184) inhibitors to mechanical and cold stimulation. By contrast, the TRPV1 antagonist AMG9810 blocked the anti-allodynic efficacy of both FAAH inhibitors, but not the MGL inhibitor. By contrast, the TRPA1 antagonist HC30031 did not attenuate anti-allodynic efficacy of any endocannabinoid modulator. When the levels of endocannabinoids were examined, cisplatin increased both anandamide (AEA) and 2-arachidonoylglycerol (2-AG) levels in the lumbar spinal cord and decreased 2-AG levels (but not AEA) in dorsal hind paw skin. RT-PCR showed that mRNA for FAAH, but not other markers, was upregulated by cisplatin treatment in lumbar spinal cord. The present studies demonstrate that cisplatin alters endocannabinoid tone and that inhibition of endocannabinoid hydrolysis alleviates chemotherapy-induced mechanical and cold allodynia. The anti-allodynic effects of FAAH and MGL inhibitors are mediated by CB(1) and CB(2) cannabinoid receptors, whereas TRPV1, but not TRPA1, -dependent mechanisms contribute to the anti-allodynic efficacy of FAAH (but not MGL) inhibitors. Strikingly, endocannabinoid modulators potently suppressed cisplatin-evoked allodynia with a rapid onset and showed efficacy that equaled or exceeded that of major classes of anti-neuropathic pain medications used clinically. Thus, inhibition of endocannabinoid hydrolysis, via FAAH or MGL inhibitors, represents an efficacious pharmacological approach for suppressing chemotherapy-induced neuropathic pain.
顺铂是一种源于铂的化疗药物,可引起机械性和冷感觉异常,使人想起人类的化疗诱导性神经病。内源性大麻素系统是开发镇痛药物的一个新靶点。内源性大麻素信号系统由内源性大麻素(如花生四烯酸乙醇胺(AEA)和 2-花生四烯酰甘油(2-AG))、大麻素受体(如 CB(1) 和 CB(2))以及控制内源性大麻素合成和降解的酶组成。AEA 被脂肪酸酰胺水解酶(FAAH)水解,而 2-AG 主要被单酰基甘油脂肪酶(MGL)水解。我们比较了脑渗透性(URB597)和非渗透性(URB937)FAAH 抑制剂与不可逆的 MGL 抑制剂(JZL184)对顺铂诱发的行为过敏的影响。将内源性大麻素调节剂与临床上用于治疗神经病的药物(即阿片类镇痛药吗啡、抗惊厥药加巴喷丁和三环抗抑郁药阿米替林)进行比较。顺铂引起明显的机械性和冷感觉异常,但不改变对热的反应性。神经病完全建立后,各组接受腹腔内(i.p.)注射载体、阿米替林(30mg/kg)、加巴喷丁(100mg/kg)、吗啡(6mg/kg)、URB597(0.1 或 1mg/kg)、URB937(0.1 或 1mg/kg)或 JZL184(1、3 或 8mg/kg)。通过与 CB(1)(AM251,3mg/kg)、CB(2)(AM630,3mg/kg)、TRPV1(AMG9810,3mg/kg)或 TRPA1(HC030031,8mg/kg)拮抗剂共给药,评估了每种内源性大麻素调节剂的药理学特异性。还评估了顺铂对与内源性大麻素系统相关的受体(CB(1)、CB(2)、TRPV1、TRPA1)和酶(FAAH、MGL)的内源性大麻素水平和转录的影响。URB597、URB937、JZL184 和吗啡逆转了顺铂引起的机械性和冷感觉异常,使其恢复到顺铂前的水平。相比之下,加巴喷丁仅部分逆转了观察到的感觉异常,而急性给予阿米替林则无效。CB(1)或 CB(2)拮抗剂完全阻断了 FAAH(URB597、URB937)和 MGL(JZL184)抑制剂对机械和冷刺激的抗感觉异常作用。相比之下,TRPV1 拮抗剂 AMG9810 阻断了 FAAH 抑制剂的抗感觉异常作用,但不阻断 MGL 抑制剂的作用。相比之下,TRPA1 拮抗剂 HC30031 并不能减弱任何内源性大麻素调节剂的抗感觉异常作用。当检查内源性大麻素水平时,顺铂增加了腰脊髓中的花生四烯酸乙醇胺(AEA)和 2-花生四烯酰甘油(2-AG)水平,并降低了背足皮肤中的 2-AG 水平(但不降低 AEA)。RT-PCR 显示,FAAH 而不是其他标志物的 mRNA 被顺铂处理上调。本研究表明,顺铂改变了内源性大麻素的张力,抑制内源性大麻素水解可减轻化疗引起的机械性和冷感觉异常。FAAH 和 MGL 抑制剂的抗感觉异常作用是通过 CB(1)和 CB(2)大麻素受体介导的,而 TRPV1 而不是 TRPA1,依赖机制有助于 FAAH(但不是 MGL)抑制剂的抗感觉异常作用。引人注目的是,内源性大麻素调节剂以快速起效和与临床上使用的主要类别的抗神经病药物相当或超过的疗效有力地抑制了顺铂引起的所有感觉异常。因此,通过 FAAH 或 MGL 抑制剂抑制内源性大麻素水解是抑制化疗诱导性神经病痛的有效药理学方法。
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