蘭 嶺 黃宇光 申 樂
(中國醫(yī)學(xué)科學(xué)院北京協(xié)和醫(yī)院麻醉科,北京 100730)
?特約綜述?
術(shù)后慢性疼痛相關(guān)炎癥反應(yīng)與免疫調(diào)節(jié)機(jī)制研究進(jìn)展*
蘭 嶺 黃宇光 申 樂△
(中國醫(yī)學(xué)科學(xué)院北京協(xié)和醫(yī)院麻醉科,北京 100730)
術(shù)后慢性疼痛具有發(fā)病率高、持續(xù)時間長、發(fā)病機(jī)制復(fù)雜等特點(diǎn),嚴(yán)重影響病人的生活質(zhì)量。手術(shù)所致神經(jīng)病理性損傷是術(shù)后慢性疼痛發(fā)生的重要機(jī)制。與此同時,手術(shù)損傷所致神經(jīng)系統(tǒng)的過度炎癥反應(yīng)和免疫調(diào)節(jié)機(jī)制亦加快術(shù)后慢性疼痛的形成。在術(shù)后慢性疼痛的發(fā)生發(fā)展過程中,神經(jīng)損傷、壞死組織炎癥反應(yīng)和/或感染均可導(dǎo)致外周神經(jīng)、DRG及脊髓背角中多種免疫細(xì)胞及膠質(zhì)細(xì)胞活化,產(chǎn)生多種促炎癥細(xì)胞因子和趨化因子,導(dǎo)致組織微環(huán)境中促炎癥細(xì)胞因子和抗炎癥細(xì)胞因子的比例失衡,外周和中樞神經(jīng)元興奮閾值下降,神經(jīng)元興奮性提高,發(fā)生痛覺敏化。本文主要綜述術(shù)后神經(jīng)系統(tǒng)炎癥反應(yīng)與免疫調(diào)節(jié)所致術(shù)后慢性疼痛的相關(guān)機(jī)制。
術(shù)后慢性疼痛;炎癥反應(yīng);免疫調(diào)節(jié)
術(shù)后慢性疼痛(chronic postsurgical pain, CPSP)是指患者存在手術(shù)相關(guān)性疼痛持續(xù)至少2個月以上且除外其他病因(如慢性感染、惡性腫瘤復(fù)發(fā)等)所致疼痛[1]。開胸手術(shù)、乳腺癌(改良)根治手術(shù)、剖宮產(chǎn)手術(shù)、截肢手術(shù)等較易導(dǎo)致CPSP,其中尤以開胸及截肢手術(shù)為著,其CPSP的發(fā)生率可高達(dá)50%~80%[2]。我們前期通過對466例接受開胸手術(shù)的患者隨訪發(fā)現(xiàn),開胸手術(shù)CPSP的發(fā)生率高達(dá)64.5%[3],嚴(yán)重影響患者術(shù)后的生活質(zhì)量。
CPSP的發(fā)生機(jī)制復(fù)雜,手術(shù)所致神經(jīng)損傷是CPSP發(fā)生的必要前提,而神經(jīng)系統(tǒng)過度的炎癥反應(yīng)和異常的免疫調(diào)節(jié)在術(shù)后急性疼痛向CPSP的轉(zhuǎn)變過程中發(fā)揮著關(guān)鍵作用[4~6]。我們前期的研究表明術(shù)后病人白細(xì)胞計(jì)數(shù)與術(shù)前的差值(ΔWBC=WBC術(shù)后-WBC術(shù)前)是導(dǎo)致CPSP的獨(dú)立危險因素,ΔWBC越大則發(fā)生CPSP的風(fēng)險越高,這提示手術(shù)后炎癥反應(yīng)在術(shù)后慢性疼痛的形成過程中發(fā)揮重要作用[3]。炎癥反應(yīng)所導(dǎo)致的CPSP具有可逆性,因此早期、及時地調(diào)控手術(shù)后神經(jīng)系統(tǒng)炎癥反應(yīng),有利于我們術(shù)后早期有針對性地進(jìn)行治療以減少術(shù)后急性疼痛向CPSP的轉(zhuǎn)變,改善患者術(shù)后的生活質(zhì)量,減輕社會經(jīng)濟(jì)負(fù)擔(dān)。本文將從神經(jīng)系統(tǒng)炎癥反應(yīng)及免疫應(yīng)答介導(dǎo)外周及中樞性痛覺敏化所致疼痛放大機(jī)制等方面,對炎癥反應(yīng)及免疫調(diào)節(jié)機(jī)制在CPSP發(fā)生發(fā)展中的作用進(jìn)行綜述。
目前關(guān)于CPSP的成因及其與急性疼痛的關(guān)系還不十分明確,其可能發(fā)生的機(jī)制包括:外周及中樞性敏化所致疼痛放大機(jī)制、中樞神經(jīng)系統(tǒng)抑制性調(diào)節(jié)缺失機(jī)制及交感神經(jīng)系統(tǒng)調(diào)節(jié)機(jī)制[7]。炎癥反應(yīng),尤其是外周及中樞神經(jīng)系統(tǒng)炎癥反應(yīng),在CPSP的形成過程中具有重要作用。
手術(shù)創(chuàng)傷后外周組織損傷部位的修復(fù)過程主要包括三個時期:炎癥反應(yīng)、炎性細(xì)胞浸潤及組織重塑。保護(hù)性炎癥反應(yīng)是機(jī)體損傷后固有免疫的重要組成部分,是促進(jìn)創(chuàng)面修復(fù)和功能重建的必要步驟[8]。急性炎癥反應(yīng)所導(dǎo)致的疼痛主要源于促炎性神經(jīng)肽,包括P物質(zhì)、降鈣素基因相關(guān)肽(calcitonin gene related peptide, CGRP)及來自損傷部位C神經(jīng)纖維神經(jīng)激肽A (neurokinin A, NKA)的釋放,都是神經(jīng)系統(tǒng)重塑過程中的重要啟動因子。急性手術(shù)創(chuàng)傷可以導(dǎo)致劇烈疼痛和痛覺超敏,但通常這種疼痛隨著創(chuàng)面的愈合會逐漸緩解。急性炎癥反應(yīng)的持續(xù)時間與創(chuàng)面的愈合速度及患者的基礎(chǔ)身體狀態(tài)有關(guān),一般持續(xù)24小時到兩周左右。創(chuàng)面修復(fù)不佳時,手術(shù)損傷部位的慢性炎癥反應(yīng)可以持續(xù)存在,從而導(dǎo)致CPSP的發(fā)生[9]。
手術(shù)損傷外周組織產(chǎn)生大量壞死物質(zhì),損傷部位壞死細(xì)胞釋放三磷酸腺苷(adenosine triphosphate,ATP)與細(xì)胞外基質(zhì)的分解產(chǎn)物等損傷相關(guān)分子模式(danger-associated molecular patterns, DAMPs)激活損傷部位肥大細(xì)胞表面受體,導(dǎo)致肥大細(xì)胞脫顆粒,進(jìn)一步釋放組胺、5-羥色胺等血管活性胺與P物質(zhì)、緩激肽等血管活性肽,可以直接敏化傷害性感覺神經(jīng)元。與此同時,嗜酸性粒細(xì)胞、巨噬細(xì)胞等被募集至損傷部位并釋放白細(xì)胞介素1β(interleukin, IL-1β)、腫瘤壞死因子 α(tumor necrosis factor, TNF-α)等多種促炎細(xì)胞因子[10]。此外,DAMPs可導(dǎo)致巨噬細(xì)胞聚集活化、吞噬壞死物質(zhì)并釋放CCL2、CX3CL1等趨化因子[11]。這些促炎細(xì)胞因子可直接或間接作用于傷害性感覺神經(jīng)元上的受體,激活神經(jīng)元內(nèi)蛋白激酶A、蛋白激酶C、p38絲裂酶原活化蛋白激酶(mitogen-activated protein kinase, MAPK)等多種復(fù)雜的信號傳導(dǎo)通路,從而降低周圍神經(jīng)元興奮閾值,產(chǎn)生短期的外周敏化[12]。當(dāng)外周炎癥反應(yīng)長期存在時,會導(dǎo)致神經(jīng)元內(nèi)相關(guān)轉(zhuǎn)錄因子水平持續(xù)上調(diào),進(jìn)而導(dǎo)致興奮性神經(jīng)遞質(zhì)細(xì)胞膜表面離子通道和受體表達(dá)水平的長期改變,造成周圍神經(jīng)元重塑和持續(xù)的外周敏化。
盡管中樞性炎癥反應(yīng)對周圍組織和/或神經(jīng)損傷所致CPSP的具體作用機(jī)制尚不明確,但多項(xiàng)研究[7,11~13]表明中樞炎癥反應(yīng)可以增強(qiáng)脊髓傷害性反射弧,使機(jī)體對傷害性刺激產(chǎn)生中樞性敏化。正常情況下,IL-1β、IL-6、TNF-α等促炎性細(xì)胞因子在脊髓中低表達(dá)。手術(shù)損傷導(dǎo)致外周傷害性感受器敏化時,大量異常興奮性電活動傳導(dǎo)至脊髓后角神經(jīng)元,導(dǎo)致其突觸前膜鈣離子通道異常開放增加,異常放電明顯加強(qiáng),P物質(zhì)、CCL2、ATP等炎癥因子釋放增加。其中,突觸前膜CCL2、ATP及神經(jīng)調(diào)節(jié)蛋白-1的表達(dá)上調(diào)釋放增加,可以促進(jìn)脊髓背角膠質(zhì)細(xì)胞(小膠質(zhì)細(xì)胞、星形膠質(zhì)細(xì)胞)大量浸潤,進(jìn)一步釋放IL-1β、組織蛋白酶S、骨源性生長因子(bone-derived growth factor,BDGF)等炎癥因子[14]。除了直接導(dǎo)致外周傷害性感受器敏化之外,脊髓背角的IL-1β還可以通過介導(dǎo)眾多其他促炎性細(xì)胞因子(如IL-6、TNF-α)的合成增加間接發(fā)揮促炎癥作用[15]。此外,突觸前膜和小膠質(zhì)細(xì)胞釋放的BDGF與突觸后膜的原肌球蛋白受體激酶B (tropomyosin receptor kinase B,TrkB)結(jié)合,導(dǎo)致K+和Cl-共同轉(zhuǎn)運(yùn)體KCC2的水平下調(diào),突觸后膜陰離子濃度梯度改變,激活γ-氨基丁酸A型受體,使Cl-外流增加,突觸后膜去極化,增加電活動,產(chǎn)生中樞敏化和神經(jīng)元重塑[16],進(jìn)一步促進(jìn)CPSP的形成。
神經(jīng)系統(tǒng)和免疫系統(tǒng)的相互作用是CPSP發(fā)生發(fā)展的重要因素。神經(jīng)損傷導(dǎo)致的炎癥性級聯(lián)反應(yīng)過程中,免疫調(diào)節(jié)及促炎細(xì)胞因子的釋放促進(jìn)CPSP的產(chǎn)生,其中神經(jīng)膠質(zhì)細(xì)胞、趨化因子及toll樣受體(toll-like receptors, TLRs)在神經(jīng)免疫應(yīng)答過程中的作用至關(guān)重要[17,18]。
中樞神經(jīng)系統(tǒng)的神經(jīng)膠質(zhì)細(xì)胞主要有三種類型:小膠質(zhì)細(xì)胞、星形膠質(zhì)細(xì)胞和少突膠質(zhì)細(xì)胞。小膠質(zhì)細(xì)胞是中樞神經(jīng)系統(tǒng)的巨噬細(xì)胞,構(gòu)成了中樞神經(jīng)系統(tǒng)的第一道免疫屏障。在機(jī)體受到化學(xué)性刺激時小膠質(zhì)細(xì)胞迅速激活,活化的小膠質(zhì)細(xì)胞遷移至脊髓背角,吞噬有害物質(zhì),分泌促炎癥物質(zhì)并且迅速增殖。它們是中樞神經(jīng)系統(tǒng)炎癥介質(zhì)的主要來源[18]。小膠質(zhì)細(xì)胞一旦被激活,將永遠(yuǎn)保持激活狀態(tài),這可能是中樞性敏化的重要因素之一。星形膠質(zhì)細(xì)胞具有維持血腦屏障、營養(yǎng)神經(jīng)元等功能,它通過和肥大細(xì)胞相互作用產(chǎn)生炎癥反應(yīng)加劇中樞性敏化[17,18]。星形膠質(zhì)細(xì)胞能夠分泌趨化因子及促炎細(xì)胞因子,導(dǎo)致傷害性神經(jīng)元興奮性增加,進(jìn)一步維持神經(jīng)炎癥反應(yīng)[19]。
趨化因子及其受體介導(dǎo)脊髓背角膠質(zhì)細(xì)胞和神經(jīng)元的相互作用,在神經(jīng)損傷誘導(dǎo)的神經(jīng)病理性疼痛的發(fā)生過程中發(fā)揮重要作用[20]。目前已發(fā)現(xiàn)的與CPSP相關(guān)的趨化因子及其受體主要有CX3CL1/CX3CR1、CCL2/CCR2等。
(1)CX3CL1
手術(shù)損傷周圍神經(jīng)產(chǎn)生神經(jīng)病理性疼痛時,CX3CR1在小膠質(zhì)細(xì)胞中的表達(dá)明顯上調(diào)。CX3CL1通過上調(diào)的CX3CR1使小膠質(zhì)細(xì)胞大量募集。同時,CX3CL1和CX3CR1的結(jié)合導(dǎo)致小膠質(zhì)細(xì)胞內(nèi)p38 MAPK磷酸化,激活p38 MAPK信號轉(zhuǎn)導(dǎo)通路,釋放多種促炎癥細(xì)胞因子,進(jìn)一步敏化中樞神經(jīng)元[21]。在坐骨神經(jīng)慢性縮窄損傷(chronic constriction injury,CCI)和坐骨脊神經(jīng)結(jié)扎(spinal nerve ligation, SNL)神經(jīng)病理性疼痛模型中,鞘內(nèi)注射CX3CR1或CX3CL1的中和抗體能夠明顯減輕機(jī)械性痛覺超敏和熱痛覺超敏[22]。行為學(xué)研究表明[23],CX3CL1能夠誘導(dǎo)大鼠和小鼠產(chǎn)生顯著的機(jī)械性痛覺超敏和熱痛覺超敏。在CX3CR1敲除小鼠中,CX3CL1不能誘導(dǎo)周圍神經(jīng)損傷后痛覺超敏的產(chǎn)生。
(2) CCL2
周圍或中樞神經(jīng)損傷會引起脊髓及背根神經(jīng)節(jié)(dorsal root ganglion,DRG)中CCL2及其受體CCR2的表達(dá)增加。其中,脊髓和DRG中小膠質(zhì)細(xì)胞和星形膠質(zhì)細(xì)胞CCL2/CCR2的表達(dá)上調(diào)尤為顯著[24]。手術(shù)損傷外周神經(jīng)產(chǎn)生神經(jīng)炎癥反應(yīng)時,CCL2/CCR2通過介導(dǎo)膠質(zhì)細(xì)胞-神經(jīng)元的相互作用參與中樞敏化和慢性疼痛調(diào)節(jié)[25]。初級傳入神經(jīng)末端釋放的CCL2可以直接導(dǎo)致小膠質(zhì)細(xì)胞的激活,進(jìn)一步促進(jìn)IL-1β、組織蛋白酶S等促炎癥因子的釋放。神經(jīng)炎癥反應(yīng)活化星形膠質(zhì)細(xì)胞內(nèi)JNK信號轉(zhuǎn)導(dǎo)通路導(dǎo)致CCL2釋放增加,CCL2作用于脊髓后角神經(jīng)元突觸后膜,加快細(xì)胞外信號調(diào)節(jié)蛋白激酶(extracellular regulated protein kinases,ERK)的磷酸化,導(dǎo)致脊髓后角淺層神經(jīng)元的敏感化。
當(dāng)中樞神經(jīng)元結(jié)構(gòu)發(fā)生損傷時,壞死的神經(jīng)細(xì)胞釋放DAMPs,進(jìn)而激活損傷部位的TLRs。TLRs是機(jī)體免疫系統(tǒng)的模式識別受體,它能夠感知傷害性刺激的發(fā)生并將刺激信號傳遞至其他神經(jīng)元和免疫細(xì)胞。動物實(shí)驗(yàn)[26]表明TLR4通過促炎性信號級聯(lián)反應(yīng)激活神經(jīng)膠質(zhì)細(xì)胞。Peirs C[27]等認(rèn)為TLR4水平上調(diào)可能是已激活的小膠質(zhì)細(xì)胞的標(biāo)志物,這預(yù)示著TLR4可能是預(yù)測CPSP發(fā)生的重要指標(biāo)。我們的研究[28,29]發(fā)現(xiàn)在CCI大鼠DRG與脊髓背角的TLR4通路都處于活化狀態(tài),利用miR-146a抑制TLR4通路的活化,將有效緩解大鼠的疼痛行為。
在術(shù)后慢性疼痛的發(fā)生發(fā)展過程中,神經(jīng)損傷、壞死組織炎癥反應(yīng)和/或感染均可導(dǎo)致外周神經(jīng)、DRG及脊髓背角中多種免疫細(xì)胞及膠質(zhì)細(xì)胞活化,產(chǎn)生多種促炎癥細(xì)胞因子和趨化因子,導(dǎo)致組織微環(huán)境中促炎癥細(xì)胞因子和抗炎癥細(xì)胞因子的比例失衡,外周和中樞神經(jīng)元興奮閾值下降,神經(jīng)元興奮性提高,發(fā)生痛覺敏化。與神經(jīng)損傷所致不可逆性術(shù)后神經(jīng)病理性疼痛不同,炎癥反應(yīng)及免疫應(yīng)答所致術(shù)后炎癥性疼痛可以被合理的治療手段所逆轉(zhuǎn)。因此,研究CPSP的發(fā)病機(jī)制,明確炎癥反應(yīng)及免疫調(diào)節(jié)在其發(fā)生和維持中的作用,探究可行的臨床治療方案,對炎癥性疼痛進(jìn)行早期合理的干預(yù),可以明顯降低CPSP的發(fā)生率,改善患者的術(shù)后生活質(zhì)量,減輕患者、家庭及社會的經(jīng)濟(jì)負(fù)擔(dān)。
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10.3969/j.issn.1006-9852.2017.03.001
國家自然科學(xué)基金(81200869)
△通訊作者 shenle@pumch.cn