李濤，劉源，黨勝春，張建新

（江蘇大學(xué)附屬醫(yī)院普外科，江蘇 鎮(zhèn)江 212001）

p38MAPK抑制劑對重癥急性胰腺炎的保護

李濤，劉源，黨勝春，張建新

（江蘇大學(xué)附屬醫(yī)院普外科，江蘇 鎮(zhèn)江 212001）

重癥急性胰腺炎臨床表現(xiàn)兇險，病因復(fù)雜，病死率高，是臨床常見的急腹癥之一，也是臨床治療的難癥之一。多種信號通路參與其發(fā)生、發(fā)展，其中p38MAPK信號轉(zhuǎn)導(dǎo)通路是目前研究的熱點。p38MAPK抑制劑是一類合成的小分子有機化合物，其可通過特異性阻斷p38MAPK信號轉(zhuǎn)導(dǎo)通路，減少重癥急性胰腺炎時炎性介質(zhì)的表達與釋放，減輕器官組織的損傷，有望成為治療重癥急性胰腺炎的有效途徑。

p38MAPK抑制劑；重癥急性胰腺炎；信號轉(zhuǎn)導(dǎo)

急性胰腺炎(Acute pancreatitis，AP)是常見的外科急腹癥，尤其是重癥急性胰腺炎(Severe acute pancreatitis，SAP)，其臨床表現(xiàn)兇險，病因復(fù)雜，病死率高達30%[1]，是目前臨床治療較為棘手的外科急腹癥之一。發(fā)生SAP時，胰腺組織廣泛出血、壞死，大量的炎癥細胞浸潤及炎癥因子釋放形成過度炎癥反應(yīng)，最終造成系統(tǒng)性炎癥反應(yīng)綜合征(Systemic inflammatory response syndrome，SIRS)，甚至導(dǎo)致多器官功能不全綜合征(Multiple organ dysfunction，MODS)。單核/巨噬細胞是產(chǎn)生多種炎癥介質(zhì)的主要細胞，炎癥介質(zhì)在SAP及其并發(fā)癥的發(fā)生發(fā)展的機制中起著重要的作用。炎癥介質(zhì)的合成在蛋白水平上主要經(jīng)過兩個信號通路：核因子(NF-κB)和p38絲裂原活化蛋白激酶(p38 mitogen-activated protein kinase，p38MAPK)通路。SAP發(fā)生時，激活p38MAPK信號轉(zhuǎn)導(dǎo)通路，可促進多種炎癥因子表達和釋放[2]，因此p38MAPK信號轉(zhuǎn)導(dǎo)通路在調(diào)控炎癥介質(zhì)表達方面有重要作用[3]。

1 p38MAPK的組成及其信號轉(zhuǎn)導(dǎo)通路

1.1 p38MAPK的結(jié)構(gòu)及功能 p38MAPK是由360個氨基酸組成的38 KD的蛋白，存在6種異構(gòu)體：p38α1/α2、p38β1/β2、p38γ和p38δ[4]，其中p38α和p38β在各種組織細胞廣泛存在。p38不僅參與細胞的發(fā)育、分化以及凋亡[5]，而且可調(diào)控多種細胞因子、炎癥介質(zhì)的表達與釋放[6]，在急性炎癥性疾病中也有至關(guān)重要的作用。MAPK的兩個臨近的磷酸化點與一個氨基酸組成一個環(huán)狀結(jié)構(gòu)的三肽基“TXY”，位于一個被稱為T狀結(jié)構(gòu)(T-loop或Loop-12 structure)的表面，T環(huán)是決定多種蛋白激酶活性的關(guān)鍵結(jié)構(gòu)[7]。激活MAPK需要臨近的蘇氨酸(Threonin，Thr180)和酪氨酸(Tyrosin，Tyrl82)同時磷酸化來完成[8]。P38MAPK的滅活同其他MAPKs一樣，也是被雙特異性蛋白磷酸酶將已磷酸化的蘇氨酸和酪氨酸殘基去磷酸化。

1.2 p38MAPK信號轉(zhuǎn)導(dǎo)通路 p38MAPK信號轉(zhuǎn)導(dǎo)通路是哺乳動物MAPK信號通路中的一條經(jīng)典途徑[9]，p38MAPK信號傳導(dǎo)通路大致為：MEKK5/ MLK3→MKK3/MKK6→p38MAPK[10]，它們構(gòu)成一條完整的連續(xù)的蛋白激酶反應(yīng)鏈。p38MAPK通路最上游的激酶主要是MEKK5、凋亡信號調(diào)節(jié)激酶(ASK)、混合譜系激酶3(MLK3)等。當(dāng)細胞受到刺激后(如炎癥刺激、應(yīng)激反應(yīng)、UV照射、LPS等)，細胞外信號與相關(guān)受體特異性結(jié)合，使MEKK5、ASK、MLK3磷酸化，促進MKK3以及MKK6基因表達，并使其表達的蛋白磷酸化，誘導(dǎo)p38MAPK基因轉(zhuǎn)錄。眾多研究表明，活化的p38MAPK參與單核/巨噬細胞、中性粒細胞的功能性反應(yīng)，同時可通過調(diào)節(jié)干擾素的生成進而調(diào)控T細胞[11]。活化的p38MAPK還可將MSK1/2、MNK1/2、MK2/3等MKs磷酸化，這些被磷酸化激活的激酶能進一步磷酸化低分子熱休克蛋白，從而參與細胞應(yīng)激反應(yīng)[12]。p38MAPK可以特異性地將ATF2(Activated transfer factor-2)的Thr71磷酸化，激活后的ATF2與核因子(NK)κB可以結(jié)合于AP1位點，正向調(diào)節(jié)細胞因子的表達。同時研究發(fā)現(xiàn)[13]，p38MAPK信號轉(zhuǎn)導(dǎo)通路并非獨立存在于機體內(nèi)，它與其他MAPKs信號轉(zhuǎn)導(dǎo)通路共同構(gòu)成信號轉(zhuǎn)導(dǎo)通路網(wǎng)絡(luò)，共同發(fā)揮作用。當(dāng)機體發(fā)生炎癥反應(yīng)時，一方面，炎癥介質(zhì)(TNF-α、IL-1等)可激活p38MAPK信號轉(zhuǎn)導(dǎo)通路[14]，誘導(dǎo)單核/巨噬細胞活化，促進組織細胞凋亡，最終形成MODS；另一方面，p38MAPK的活化可促進大量的炎癥因子合成[15]，激活其他信號轉(zhuǎn)導(dǎo)通路，具有放大炎癥反應(yīng)的作用。

2 p38MAPK與SAP

SAP的發(fā)病過程十分復(fù)雜，其中信號轉(zhuǎn)導(dǎo)通路介導(dǎo)的炎癥介質(zhì)瀑布樣級聯(lián)反應(yīng)最為人們關(guān)注。發(fā)生SAP時，受損的胰腺細胞可激活單核/巨噬細胞、淋巴細胞等產(chǎn)生和釋放炎癥介質(zhì)(TNF-α、IL-1、IL-6等)，這些炎癥介質(zhì)可進一步激活更多的炎癥細胞，促使它們向炎癥組織粘附、外滲、聚集，釋放大量炎癥介質(zhì)，因此SAP患者血清檢驗可發(fā)現(xiàn)有大量的炎癥介質(zhì)[16]。上述過程構(gòu)成放大炎癥反應(yīng)，最終導(dǎo)致胰腺組織的進一步損傷，甚至造成胰腺外器官的損傷。近年來，p38 MAPK信號轉(zhuǎn)導(dǎo)通路成為研究SAP發(fā)病機制中的熱點[17]。施新崗等[18]實驗研究發(fā)現(xiàn)，成功構(gòu)建SAP大鼠模型后，大鼠胰腺組織的p38MAPK在15 min內(nèi)迅速磷酸化達到峰值，并維持在較高水平，3 h后磷酸化水平逐漸下降，6 h后基本恢復(fù)正常，提示p38MAPK信號轉(zhuǎn)導(dǎo)通路在SAP的發(fā)病過程中起重要作用。研究發(fā)現(xiàn)[19]，早期胰腺細胞受損后，TNF-α、IL-1、IL-6等炎癥介質(zhì)釋放使胰腺細胞p38MAPK磷酸化，激活p38MAPK信號轉(zhuǎn)導(dǎo)通路。有研究表明[20]，SAP的嚴重程度與p38MAPK磷酸化程度密切相關(guān)，細胞內(nèi)儲存的p38MAPK磷酸化比例增高，SAP越嚴重。另一方面，p38MAPK信號轉(zhuǎn)導(dǎo)通路激活后活化其他信號轉(zhuǎn)導(dǎo)通路，進一步加重SAP的炎癥反應(yīng)。雨蛙素構(gòu)建的SAP大鼠模型中，胰腺腺泡細胞內(nèi)p38MAPK的磷酸化水平顯著上升，同時伴有NF-κB的激活[21]，NF-κB亞基的活化過程有p38MAPK信號轉(zhuǎn)導(dǎo)通路的參與，NF-κB活化可導(dǎo)致更多的炎性介質(zhì)釋放，使得炎癥進一步加重，導(dǎo)致級聯(lián)瀑布效應(yīng)，使得SAP嚴重程度加劇，進而為局部炎癥向全身發(fā)展提供了契機。因此p38MAPK信號轉(zhuǎn)導(dǎo)通路具有放大炎癥反應(yīng)的作用[14，22-23]。

3 p38MAPK抑制劑保護SAP

p38MAPK抑制劑是一類合成的小分子有機化合物，具有良好的抗炎作用，多用于對抗炎癥性腸病、類風(fēng)濕性關(guān)節(jié)炎、骨關(guān)節(jié)炎、肺炎等疾病中的炎癥反應(yīng)[24-27]。目前發(fā)現(xiàn)的p38MAPK抑制劑只有幾種，如SB203580、SB216995、SB220025、VK199、SB239063、CNI-1493。目前應(yīng)用最廣泛的抑制劑為SB203580，其次為CNI-1493。SB203580為吡啶咪唑類衍生物，其作用機制是競爭性結(jié)合p38MAPK上的ATP結(jié)合位點，抑制p38MAPK的活化，從而減輕炎癥反應(yīng)[28]。研究表明，SB203580與是否具有活性的p38MAPK的親和力無明顯差別，SB203580只是競爭性地結(jié)合于p38MAPK的ATP位點阻止其磷酸化下游靶點ATF2，進而阻斷p38MAPK酶的活性[29-30]，其并不影響機體內(nèi)正常p38MAPK的磷酸化。另一方面，SB203580可抑制刺激所誘導(dǎo)的p38MAPK的Thr-Gly-Thr基因的磷酸化，即通過結(jié)合p38MAPK的非活化形式，減少p38MAPK的活化比率[31]。彭蘭等[32]研究發(fā)現(xiàn)SB203580阻斷p38MAPK信號轉(zhuǎn)導(dǎo)通路，減少細胞因子的釋放，使得胰腺腺泡細胞NF-κB的轉(zhuǎn)錄水平下降，NF-κB活化受到抑制，進一步減少炎癥介質(zhì)的釋放，從而減輕炎癥介質(zhì)瀑布樣級聯(lián)反應(yīng)，使SAP炎癥反應(yīng)得到有效的控制[21]。CNI-1493是一種四價的鳥苷酸腙分子，能夠激活膽堿能抗炎通路，阻止p38MAPK的磷酸化，進而抑制單核/巨噬細胞釋放炎癥介質(zhì)[33]。研究表明，CNI-1493通過抑制多形核粒細胞的氧化呼吸爆發(fā)，減少氧自由基(Oxygen free radical)及髓過氧化物酶(Myeloperoxidase，MPO)的產(chǎn)生與釋放，使得p38MAPK磷酸化水平受到抑制，p38MAPK信號轉(zhuǎn)導(dǎo)通路難以激活，減輕SAP炎癥反應(yīng)[34]。

4 展 望

綜上所述，p38MAPK抑制劑在抑制SAP炎癥反應(yīng)有著良好的應(yīng)用前景，但多種信號轉(zhuǎn)導(dǎo)通路相互交匯，形成一個錯綜復(fù)雜的信號轉(zhuǎn)導(dǎo)網(wǎng)絡(luò)，使得SAP的發(fā)病機制十分復(fù)雜，其中p38MAPK與其他信號分子有著廣泛而又密切的聯(lián)系。Chang等[35]研究表明，TNF-α的表達及其發(fā)揮生物學(xué)功能，不僅受到p38MAPK的調(diào)控，同時受到其他炎癥介質(zhì)的影響。在介導(dǎo)SAP的多種信號轉(zhuǎn)導(dǎo)通路中，存在著與p38MAPK相似的蛋白，這一特點使得針對p38MAPK的靶向抑制治療具有“雙刃劍”的特點：一方面，使用p38MAPK抑制劑，可抑制p38MAPK的活化，從而阻斷p38MAPK信號轉(zhuǎn)導(dǎo)通路，減少相關(guān)炎癥介質(zhì)的產(chǎn)生與釋放，控制疾病的發(fā)展，從而達到治療疾病的目的；另一方面，抑制p38MAPK不可避免地會影響與p38MAPK相似的蛋白，存在抑制甚至阻斷其他信號轉(zhuǎn)導(dǎo)通路的可能，從而產(chǎn)生無法預(yù)測的效應(yīng)[36]。由于抑制p38MAPK可對其他器官產(chǎn)生不同的影響，因此，應(yīng)該進一步深入研究p38MAPK信號轉(zhuǎn)導(dǎo)通路的特點，找準有關(guān)靶點，研發(fā)出高效特異的p38MAPK抑制劑。

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Protection of p38MAPK inhibitor on severe acute pancreatitis.

LI Tao,LIU Yuan,DANG Sheng-chun,ZHANG Jian-xin.Department of General Surgery,the Affiliated Hospital of Jiangsu University,Zhenjiang 212001,Jiangsu,CHINA

Severe acute pancreatitis,one of the most common clinical acute abdominal diseases and one of the difficult diseases in clinical treatment,often happens in emergency with complex etiology and leads to high mortality. Multiple signaling pathways are involved in the pathogenesis and progression of severe acute pancreatitis,in which p38MAPK signal transduction pathway is the most notable.P38MAPK inhibitors,a kind of synthesis of small molecular organic compounds,by their specificity can suppress the expression and release of inflammatory mediators and can relieve the tissues injury.Thus,p38MAPK inhibitors are expected to become the effective way for treatment of severe acute pancreatitis.

P38MAPK inhibitor;Severe acute pancreatitis;Signal transduction pathway

R657.5+1

A

1003—6350（2016）03—0444—03

2015-09-23)

江蘇省自然科學(xué)基金(編號：BK2012704)；江蘇省鎮(zhèn)江市社會發(fā)展項目(編號：SB2013022)

張建新。E-mail：zhangjx@ujs.edu.cn

doi∶10.3969/j.issn.1003-6350.2016.03.035