医学科普
辣椒素对内脏痛觉过敏的影响及机制
张琴，谭婷婷 彭燕Effect and mechanism of action of capsaicin on visceral hyperalgesiaQin Zhang,Ting-Ting Tan,Yan PengQin Zhang, Ting-Ting Tan, Yan Peng，Department of Gastroenterology, Affiliated Hospital of Luzhou Medical College,Luzhou 646000,Sichuan Province,ChinaCorrespondence to:Qin Zhang, Department of Gastroenterology,Affiliated Hospital of Luzhou Medical College,Luzhou 646000,Sichuan Province, China. ziqing0020@sina.comReceived： Revised：AbstractCapsaicin(CAP) has multiple pharmacological actions,and research has been centered on its effect on visceral hyperalgesia(VHL). Relevant studies have shown that low doses of CAP may cause VHL to happen,and high doses can inhibit VHL. The mechanism of action of CAP on VHL may involve vanilloid receptor subtype 1(VR1),VR1’s phosphorylation and dephophory- lation,substance P(SP), calcitonin-gene-related peptide(CGRP) and protease-activated receptor 2(PAR2).CAP has promised as a new drug for VHL.Keywords:capsaicin; visceral hyperalgesia;effect;mechanismZhang Q, Peng Y.Effect and mechanism of action of capsaicin on visceral hyperalgesia.摘要辣椒素（capsaicin，CAP）药理作用广泛，其对内脏痛觉过敏（visceral hyperalgesia，VHL）的影响已引起广大学者的关注。研究显示小剂量CAP可能诱发VHL，而大剂量的CAP可能对VHL有抑制作用。CAP对VHL的作用机制可能与CAP受体（ vanilloid receptor subtype 1，VR1)及其VR1的磷酸化和去磷酸化、P物质（SP）、降钙素基因相关肽（CGRP）、蛋白水解酶激活型受体2（protease-activated receptor 2, PAR2 ）等有关。CAP可能成为一种有前景的治疗VHL的新药。关键词：辣椒素；内脏痛觉过敏；机制0 引言功能性胃肠疾病是近年来导致消化病谱变化的主要因素，此类疾病发病机制仍不清楚，患者及实验动物表现出内脏痛觉过敏（visceral hyperalgesia，VHL）[1-6]。然而目前改善VHL的药物较少，且作用不理想，随着对CAP的深入研究及VR1的克隆表达，VR1基因敲出小鼠模型的建立，CAP及VR1对VHL的作用已受到越来越多的关注。本文就CAP对VHL的研究进展作一综述。1 CAP、CAP受体及其作用CAP是辣椒中的主要辛辣成分，其药理作用广泛，具有镇痛、止痒、抗氧化等作用。大量研究显示CAP对带状疱疹后遗神经痛、三叉神经痛、糖尿病神经痛等有显著疗效。20世纪50年代，Jancso提出CAP参与了激活感知痛觉的神经元的活动。此后，有关CAP在疼痛中的研究愈来愈多。CAP是通过初级传人神经元末梢和胞膜上特殊的分子受体介导而产生作用的，这一受体称为VR1 [7-10]，它是一类表达在感觉神经末梢上的受体，同时也是一个配体门控的非选择性阳离子通道，属于瞬时感受器电位通道(TRP channel，transient receptor potential channe1)家族，又称TRPV1[11]。VR1广泛分布在脊髓背根神经节、三叉神经节和迷走神经节的中、小神经元上，因此被认为是一种神经系统特异的受体[12-13]。近年来发现，一些非神经组织也有VR1的分布，如膀胱上皮、肝、肺、胃肠道、肥大细胞、巨噬细胞等[14-17]。VR1除了可被辣椒素类物质激活外,在体内还可被伤害性热刺激(>43℃)和酸性环境(pH或腹泻等症状的IBS患者的直肠肌层粘膜下层及粘膜层VR1阳性细胞增加，患者直肠对热刺激及直肠扩张刺激敏感性增强，说明VR1在IBS的发病过程及内脏痛觉过敏的产生中可能起作用。我国学者梁杰贤等[41,42]研究显示大鼠去除VR1神经元后，对CAP的刺激不敏感，在直结肠扩张刺激下也不产生内脏痛觉过敏．也说明VR1参与了IBS的VHL的形成。Winston J等[43,44]在大鼠初生时期给予短暂的伤害性刺激导致大鼠永久的内脏感觉障碍，并证实在使用伤害性刺激之前使用VR1拮抗剂的大鼠对内脏扩张刺激敏感性降低，说明了VR1在VHL的形成和维持中都起着十分重要的作用。4 CAP在VHL中的作用机制CAP在内脏痛觉过敏形成中的作用机制非常复杂，至今尚不完全清楚。大量研究显示，VR1虽然广泛分布于背根神经节、三叉神经节和迷走神经节中的神经元上，但在腹腔内脏传入神经中的分布多于躯体传入神经，在倡导粘膜下神经丛和肌间神经丛均有VR1阳性神经元分布，从而对内脏痛产生一定作用，其机制主要与下列因素有关。4.1 SP 大多数试验表明,CAP的镇痛作用是通过与含SP的一级感觉神经终端膜上的某些化合物牢固结合,使SP释放增多、合成中断而衰竭导致;此过程亦有CGRP和NO参加。大剂量的CAP（≥50 mg／kg）可产生神经毒性作用,使细胞内的组织失去统一性开始分解,破坏了感觉神经的微管系统致使顺行性和逆行性轴索运输缺如,因此微管系统的生化过程被破坏,使末梢或中枢合成SP的神经肽蓄积减少或补充受到抑制。另外还干扰传入神经的营养因子的逆向转运。该因子有使SP减少的作用,随着SP合成的不断减少,数天或数小时后SP逐渐耗竭,随之,产生CAP易感种属动物不可修复的感觉丧失。4.2 CGRP CGRP是一种致炎、致痛的初级传入痛觉递质，富含于CAP敏感性传入神经纤维中。章菲菲等[45]在大鼠胃内置入气囊，诱发大鼠内脏痛觉过敏，观察伤害性扩张或静注CGRP对大鼠疼痛阈值的影响及给予CGRP受体拮抗剂hCGRP8-37后疼痛阈值的变化，结果显示CGRP能使大鼠疼痛阈值降低，hCGRP8-37能逆转伤害性扩张和CGRP引起的内脏敏感性增高。有研究显示全身应用CAP可使CGRP耗竭[46]，佟世义等[47]通过行为学、免疫组化观察正常大鼠硬膜外间隙注射CAP的镇痛效果，发现注射0.1%CAP组由于浓度较低，神经刺激作用较小，使初级痛觉传入纤维释放的CGRP较少，且痛阈升高可能仅由其阻断作用引起；而注射0.2%CAP组可引起CGRP大量释放，而CAP的短期镇痛效应可能是由初级痛觉递质耗竭和转运障碍双重因素引起的。这些均说明了CGRP在CAP所致的痛觉过敏中起着非常重要的作用。4.3 VR1的磷酸化和去磷酸化 VR1的磷酸化和去磷酸化调节着其对刺激物的敏感性，Mandadi S等[48.49]实验结果证明，去磷酸化的VR1产生急性脱敏，重新磷酸化后可以恢复对CAP的敏感性，这对于痛觉过敏和镇痛有重要意义。炎症时可以产生许多细胞因子，如PGE2、缓激肽等，同时局部的温度和H+浓度较高。大多数细胞因子可以激活PKA而使感觉神经末梢的VR1对温度和H+高度敏感[50.51],这可能与炎症时疼痛和热痛觉过敏有关。VR1的功能受很多因素影响，如细胞因子和蛋白激酶等，而蛋白激酶又是通过其对VR1的磷酸化和去磷酸化调节而发挥作用。Lee等[52]用CAP处理转染VR1的HEK（人胚肾）293细胞后，发现VR1对CAP的反应增强，同时伴有VR1的磷酸化显著增加， Mohapatra等[53]的实验进一步说明FSK通过激活PKA而使VR1对CAP的敏感性增强，并且PKA磷酸化Thr 370在VR1敏感性增强中起着关键作用。Wang等[54-57]研究证实，蛋白激酶C直接磷酸化VR1的ser 116而增强CAP对温度及酸的反应性。可以预测，抑制PKA和PKC的激活，或者抑制TRPV1的某些关键部位的磷酸化，将产生良好的镇痛效应，这或许是将来镇痛药开发研究的方向。4.4 PAR2 研究显示，多种物质可通过易化VR1的作用引起VHL,PAR2 被激活时可以激活蛋白激酶C（protein kinase c,PKC），从而增强VR1对CAP的敏感性[58-61]，大鼠结肠内给药，可引起内脏痛觉过敏[62-66]，梁杰贤等[41]的研究显示，通过PKC途径激活VR1从而引起实验大鼠VHL是可能的原因之一。Amadesi S等[59,60]报道注射PAR2拮抗剂可导致实验大鼠持久的热痛觉过敏，而这种情况却可以被使用VR1拮抗剂或缺少VR1者所抑制，且CAP诱导的VHL也可以被缺失VR1或使用PKC拮抗剂后抑制。同时还发现PAR2能同时激活PKCe和PKA,后两者磷酸化VR1，而增强其敏感性，这可能与炎症时的痛觉过敏有关。5 结论总之，CAP及其受体仍是目前研究的热点，其对VHL的形成和维持有重要作用,可能通过SP、CGRP、VR1的磷酸化与去磷酸化及PAR2产生作用，然而这仅仅是一个粗略的了解，参与其中的分子及其相互间的作用等仍有许多不够明确之处，进一步探讨CAP与VHL的关系,对认识CAP新用途和对VHL的治疗具有重要意义，同时也对功能性胃肠病的治疗开辟了一条新的途径。6 参考文献：[1]Drossman DA. 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