中华急诊医学杂志  2020, Vol. 29 Issue (5): 675-681   DOI: 10.3760/cma.j.issn.1671-0282.2020.05.013
PARP-1通过NF-κB信号通路对重症急性胰腺炎致肠黏膜屏障损伤的作用机制
弥亮钰1 , 吴自谦1 , 潘新亭1 , 万有栋1 , 吕韶燕1 , 朱青云2 , 宋婧宇1 , 王芸芸1 , 林天娇1     
1 山东省青岛大学附属医院急诊重症医学科 266000;
2 山东省青岛大学附属医院超声科 266000
摘要: 目的 探讨PARP-1[poly(ADP-ribose)polymerase-1,聚腺苷酸二磷酸核糖转移酶-1]在重症急性胰腺炎(severe acute pancreatitis, SAP)大鼠肠黏膜屏障损伤中的作用机制。方法 20只Wistar大鼠按随机数字表法分为CON组(对照组)、SAP组、3-AB组(即PARP-1抑制剂组)、3-AB-CON组,每组各5只。腹腔注射雨蛙素及脂多糖制作SAP大鼠模型,CON组仅注射等体积生理盐水,3-AB组于建模前0.5 h注射3-AB溶液30 mg/kg,3-AB-CON组腹腔注射3-AB溶液30 mg/kg 0.5 h后处理同CON组。各组大鼠建模后12 h处死,观察各组腹腔内大体改变,取心脏血、胰腺和肠组织,光镜下观察胰腺组织及肠组织病理形态学改变,采用酶联免疫吸附试验(ELISA)检测血清白细胞介素-6(IL-6)含量,使用全自动生化仪检测血清淀粉酶含量,采用蛋白免疫印迹试验(Western Blot)测定肠组织PARP-1、胞核核转录因子-κB(NF-κB)的蛋白表达,采用免疫组化试验测定肠黏膜Occludin蛋白表达。计量资料多组间比较采用单因素方差分析,方差不齐时则用秩转换的非参数检验,以P < 0.05为差异有统计学意义。结果 与CON组比较,SAP组大鼠腹腔明显腹水,胰腺病理明显出血坏死,肠组织绒毛结构紊乱,淀粉酶、IL-6水平升高,肠组织PARP-1、NF-κB蛋白表达明显增多,肠黏膜Occludin蛋白表达减少,说明PARP-1可诱导NF-κB活化和炎症损伤,导致胰腺及肠损伤。3-AB-CON组与CON组各指标比较差异无统计学意义。与SAP组比较,3-AB组胰腺及肠组织损伤明显减轻,淀粉酶、IL-6水平明显降低[淀粉酶(U/L)(1 879.25±736.66)vs(5 569.33±1 993.48),IL-6(pg/mL)(77.98±20.65)vs (209.14±79.08),均P < 0.05], 肠组织PARP-1、胞核NF-κB蛋白表达减少[PARP-1(灰度值)(1.44±0.09)vs (1.49±0.13),NF-κB(灰度值)(0.63±0.09)vs (0.96±0.08), 均P < 0.05],肠黏膜Occludin蛋白表达增多[评分(6.7±1.5)vs (3.2±1.1),P < 0.05]。结论 抑制PARP-1表达对SAP肠黏膜屏障损伤有保护作用,其作用机制可能是通过抑制NF-κB信号通路、增加肠黏膜Occludin蛋白表达有关。
关键词: 重症急性胰腺炎    肠黏膜屏障    PARP-1    NF-κB    Occludin蛋白    
The mechanism of poly (ADP-ribose) polymerase on the intestinal mucosal barrier injury in rat model with severe acute pancreatitis through NF-κB signaling pathway
Mi Liangyu1 , Wu Ziqian1 , Pan Xinting1 , Wan Youdong1 , Lyu Shaoyan1 , Zhu Qingyun2 , Song Jingyu1 , Wang Yunyun1 , Lin Tianjiao1     
1 Emergency Intensive Care Unit, the Affiliated Hospital of Qingdao University, Qingdao 266000, China;
2 Department of Ultrasound, the Affiliated Hospital of Qingdao University, Qingdao 266000, China
Abstract: Objective To investigate the effects of poly (ADP-ribose) polymerase-1(PARP-1) in intestinal mucosal barrier injury in rat model with severe acute pancreatitis (SAP). Methods Twenty healthy male Wistar rats were divided into four groups (n=5 each group) using a random table method: control, SAP, 3-aminobenzamide (3-AB), and 3-AB control groups. The SAP model was induced by intraperitoneal injection of cerulean with lipopolysaccharide. At 30 min, the rats were treated with the PARP-1 inhibitor, 3-AB, or normal saline, separately. After 12 h, all rats were sacrificed to harvest pancreas tissues, intestines tissues, and blood from the hearts for index detection. Serum amylase (AMY) and interleukin (IL)-6 levels were measured using an automatic biochemical instrument and enzyme-linked immunosorbent assay (ELISA), respectively.The protein expression of PARP-1 and nuclear factor (NF-κB) were measured using Western blot and that of occludin was measured using an immunohistochemical test. One-way analysis of variance was used for comparison of multiple groups of variables. Non-parametric tests of rank conversion were used when variances were not uniform. A P < 0.05 was considered statistically significant. Results Compared to the control group, the following indexes in the SAP group were significantly increased: ascites (with serious hemorrhage and necrosis in the pancreas and disordered intestinal villi), serum AMY and IL-6 levels, and the expression of PARP-1 and NF-κB. However, Occludin expression was significantly decreased. There was no significant difference between 3-AB group and 3-AB control group. Compared to the SAP group, the severity of SAP and pancreatitis-associated intestinal injury was significantly attenuated with the administration of 3-AB. Serum AMY and IL-6 levels were significantly decreased (serum AMY: 1 879.25 ± 736.6 U/L vs 5 569.33 ± 1993.48 U/L; IL-6: 77.98 ± 20.65 pg/mL vs 209.14 ± 79.08 pg/mL, both P < 0.05), but the expression of PARP-1 and NF-κB were significantly increased (PARP-1: 1.44 ± 0.09 vs 1.49 ± 0.13; NF-κB: 0.63 ± 0.09 vs 0.96±0.08, both P < 0.05). Similarly, Occludin expression was significantly decreased (6.7±1.5 vs 3.2±1.1, P < 0.05). Conclusions Inhibition of PARP-1 has protective effects on SAP associated intestinal mucosal barrier damage. The mechanism may be related to the inhibition of NF-κB signaling pathway and increase intestinal mucosal Occludin protein expression.
Key words: Severe acute pancreatitis    Intestinal mucosal barrier    Poly (ADP-ribose) polymerase-1    NF-κB    Occludin protein    

重症急性胰腺炎(severe acute pancreatitis,SAP)是胰腺炎最凶险的一种类型,具有发病率高及病死率高的特点。SAP晚期,由于肠黏膜屏障损伤导致肠道菌群移位,内毒素及细菌进入血液循环,导致菌血症、感染性坏死、多脏器功能不全综合征(multiple organ dysfunction syndrome, MODS),甚至死亡,是SAP患者病死率第二峰值的主要原因[1-2]。PARP-1是一种广泛存在于除酵母菌以外的所有真核细胞中的多功能蛋白修饰酶,主要参与细胞翻译后蛋白的修饰工作,近期研究显示其在免疫应答中也起着重要作用,可调节NF-κB及其下游细胞因IL-6、TNF-α,从而参与炎症反应[1, 3]。研究表明其参与了SAP过程中肝脏、肺、肾上腺等多个器官的损伤[4],但对SAP肠黏膜屏障的影响还有待深入研究及讨论。本研究通过雨蛙素联合脂多糖建立Wistar大鼠SAP模型,检测SAP大鼠肠黏膜PARP-1、NF-κB和紧密连接蛋白Occludin的表达,并通过使用PARP抑制剂3-氨基苯甲酰胺(3-aminobenzamide, 3-AB)探讨PARP-1对SAP大鼠肠黏膜屏障影响的作用机制。

1 材料与方法 1.1 实验动物、试剂及分组

健康雄性Wistar大鼠,体质量250~350 g,由青岛大学附属医院黄岛院区动物实验中心、济南朋悦实验动物繁育有限公司提供。雨蛙素、脂多糖、PARP-1抑制剂3-氨基苯甲酰胺(3-aminobenzamide,3-AB)购自美国MedChem Express公司,PARP抗体、NF-κB抗体、Occludin抗体购自英国abcam公司,白细胞介素-6(IL-6)酶联免疫吸附试验(ELISA)检测试剂盒购自中国Elabscience公司,全自动生化仪购自美国强生公司。

将20只Wistar大鼠适应性喂养2周,按随机数字表法分为CON组(对照组)、SAP组、3-AB组、3-AB-CON组。大鼠处理前禁食24 h,不禁水。SAP组大鼠给予雨蛙素50 μg/kg间隔1 h腹腔注射,共6次,最后1次腹腔注射雨蛙素1 h后追加脂多糖10 mg/kg[5]。3-AB组于建模前0.5 h注射3-AB 30 mg/kg,其余处理同SAP组。CON组间隔1 h注射等体积生理盐水,共7次。3-AB-CON组提前0.5 h注射3-AB 30 mg/kg,后间隔1 h注射等体积生理盐水,共7次。各组术后禁食,不禁水,分别于建模后12 h处死大鼠,取材。

1.2 实验方法 1.2.1 腹腔内大体改变

观察腹腔内炎症情况,有无腹水、腹腔皂化斑,胰腺有无出血、坏死,肠管有无充血、水肿、坏死。

1.2.2 血清指标测定

采用全自动生化仪测定各组大鼠血清淀粉酶水平。

1.2.3 胰腺病理学检查

取胰腺组织,4%甲醛溶液固定,脱水、包埋、切片、苏木精-伊红(HE)染色,封固后光镜下观察切片。根据Schmidt提出的胰腺病理评分标准,按水肿、腺泡坏死、出血和脂肪坏死、炎症和血管炎性细胞浸润等病理改变,进行胰腺病理学评分。

1.2.4 肠黏膜病理评分

取末端回肠5 cm,4%甲醛溶液固定,脱水、包埋、切片、HE染色,光镜下观察切片。根据Chiu等[6]提出的肠黏膜病理评分标准,0级肠黏膜上皮细胞排列及绒毛结构正常;Ⅰ级肠黏膜上皮细胞结构基本正常,但肠黏膜可见绒毛顶端上皮下间隙增宽;Ⅱ级肠黏膜上皮细胞排列发生紊乱,绒毛下间隙明显扩大或绒毛上皮与固有层开始剥离;Ⅲ级肠黏膜上皮进一步紊乱,绒毛上皮大片状脱落;Ⅳ级肠黏膜上皮质破坏明显,绒毛上皮完全脱落或完全缺损;Ⅴ级肠黏膜黏膜下层及固有膜断裂、崩断,发现出血和溃疡等现象,观察各组肠黏膜损伤程度。

1.2.5 血清炎症因子检测

心脏取血法取血,室温静置30 min,分离血清,ELISA法测血清中IL-6浓度,加样,覆膜置于37℃温箱90 min,甩干,加生物素抗体,置于温箱1 h,甩干,洗涤液洗3次,加酶结合工作液,置于温箱30 min,甩干,洗涤液350 μL洗5次,底物溶液显色,酶标仪分析。

1.2.6 蛋白质免疫印迹试验(Western Blot)测定肠组织PARP-1、NF-κB蛋白表达

取大鼠回肠组织,提取蛋白,BCA法测定蛋白浓度,SDS-PAGE凝胶电泳,蛋白电转移和膜封闭,抗原抗体反应,化学发光法显影,应用Image J图像分析软件进行分析,以目的条带与相应内参条带灰度值比值反映目的蛋白的表达水平。

1.2.7 免疫组化法测定肠黏膜Occludin蛋白表达

石蜡切片脱蜡、水化,H2O2孵育,抗原修复,封闭,一抗孵育,4℃过夜,HRP-羊抗兔Ig-G室温孵育20 min,SP法,DAB显色,显微镜下观察显色反应,苏木精复染,氨水溶液返蓝,按低到高浓度乙醇脱水,二甲苯透明,封片,观察并拍照。

1.3 统计学方法

应用SPSS 23.0统计软件进行统计分析,计量资料若服从正态分布则以均数±标准差(Mean±SD)表示,多组间比较采用单因素方差分析(one-way ANOVA);不符合方差齐性则用秩转换的非参数检验,利用Graphpad prism 7.0作图,以P < 0.05为差异有统计学意义。

2 结果 2.1 腹腔内大体改变

肉眼观察可见CON组大鼠胰腺大小正常,无水肿、出血、坏死,肠形态正常,无出血、坏死,腹腔内无腹水;SAP组胰腺明显出血坏死,可见少量皂化斑,肠壁出血坏死,腹腔内大量血性腹水;3-AB组胰腺水肿,较SAP组明显减轻,肠壁少量出血,腹水较SAP组明显减少;3-AB-CON组胰腺及肠管均正常(图 1)。

图 1 四组大鼠腹腔器官改变 Fig 1 Changes in abdominal organs of rats in four groups
2.2 血清淀粉酶检测及胰腺病理学检查

SAP组血清淀粉酶浓度明显较CON组增加,差异有统计学意义(P < 0.05);SAP组较3-AB组淀粉酶浓度更高,差异有统计学意义(P < 0.05), 见表 1图 2A

表 1 各组大鼠血清淀粉酶水平及胰腺病理学评分(Mean±SD) Table 1 Serum amylase levels and pancreatic pathology scores of rats in each group (Mean ± SD)
指标 CON组 SAP组 3-AB组 3-AB-CON组
血清淀粉酶
(U/L)
930.67±46.46b 5 569.33±1 993.48a 1 879.25±736.66b 790.82±18.38b
Schmid胰腺病理评分(分) 1.6±1.1b 13.3±4.6a 4.7±2.1b 1.5±1.3b
注:与CON组对比,aP < 0.05;与SAP组对比,bP < 0.05

A为各组大鼠血清淀粉酶表达水平的定量分析;B为各组大鼠Schmid胰腺病理评分的定量分析;与CON组比较,aP < 0.05;与SAP组比较,bP < 0.05 图 2 血清淀粉酶水平和胰腺病理的变化 Fig 2 Serum amylase level and pancreatic pathological changes of pancreas

光学显微镜下CON组及3-AB-CON组胰腺结构组织正常,未见明显水肿、腺泡坏死、出血和脂肪坏死;SAP组及3-AB组可见不同程度胰腺组织损伤。SAP组可见胰腺组织弥漫叶间隙、细胞间隙扩张,多区域细胞坏死、出血及脂肪坏死,多小叶炎症和血管炎性细胞浸润。3-AB组胰腺组织水肿、腺泡坏死及炎性细胞浸润均较SAP组有不同程度地减轻。Schmid胰腺病理评分显示,SAP组较CON组损伤严重,差异有统计学意义(P < 0.05),3-AB组较SAP组损伤减轻,差异有统计学意义(P < 0.05), 见表 1图 2BC

2.3 肠黏膜病理学检查及免疫组化法测定大鼠肠黏膜Occludin蛋白表达

光学显微镜下CON组及3-AB-CON组肠黏膜组织结构正常,绒毛排列整齐,无缺损;SAP组及3-AB组可见不同程度肠黏膜组织损伤。SAP组肠黏膜上皮细胞排列紊乱,绒毛形态不规则,肠黏膜内炎症细胞浸润。3-AB组肠黏膜上皮细胞排列及绒毛结构均有破坏,病理评分较SAP组有不同程度减轻,差异有统计学意义(P < 0.05),见表 2图 3AC

表 2 各组大鼠肠黏膜病理学评分、肠黏膜Occludin蛋白表达评分(Mean±SD) Table 2 Rat intestinal mucosa pathology score and intestinal mucosal Occludin protein expression score in each group (Mean±SD)
指标 CON组 SAP组 3-AB组 3-AB-CON组
肠黏膜病理评分(分) 3.8±1.3b 34.1±5.1a 22.7±3.8ab 3.8±1.5b
肠黏膜Occludin蛋白表达(分) 15.5±3.1b 3.2±1.1a 6.7±1.5ab 14.6±4.2b
注:与CON组对比,aP < 0.05;与SAP组对比,bP < 0.05

A为各组大鼠肠黏膜病理评分的定量分析;B为各组大鼠肠黏膜Occludin蛋白表达评分的定量评分;C为代表性HE染色法检测四组肠黏膜病理学变化(×200);D为代表性免疫组化法测定四组大鼠肠黏膜Occludin蛋白表达情况(×400);与CON组对比,aP < 0.05;与SAP组对比,bP < 0.05 图 3 大鼠肠黏膜病理学检查及Occludin蛋白免疫组化染色情况 Fig 3 Pathological examination of intestinal mucosa and immunohistochemical staining for Occludin protein in rats

免疫组织化学法结果显示,CON组大鼠肠黏膜Occludin蛋白沿肠黏膜上皮细胞分布,呈很强的棕褐色信号;3-AB组棕褐色信号有所减弱;SAP组阳性细胞明显减少。SAP组和3-AB组肠黏膜组织Occludin蛋白明显较CON组表达减少,差异有统计学意义(P < 0.05);3-AB组较SAP组表达增多,差异有统计学意义(P < 0.05),见表 2图 3BD

2.4 Western Blot法观察大鼠肠黏膜组织PARP-1、NF-κB表达及血清IL-6表达

SAP组血清IL-6浓度较CON组明显升高,差异有统计学意义(P < 0.05);SAP组较3-AB组浓度更高,差异有统计学意义(P < 0.05),见表 3图 4A

表 3 各组大鼠血清IL-6水平及肠黏膜组织PARP-1、NF-κB表达(Mean±SD) Table 3 Serum level of IL-6 and expressions of PARP-1 and NF-κB in intestinal mucosa of rats in each group (Mean±SD)
指标 CON组 SAP组 3-AB组 3-AB-CON组
血清IL-6(pg/mL) 47.99±24.88b 209.14±79.08a 77.98±20.65b 54.26±43.43b
PARP-1/GAPDH 0.37±0.04b 0.96±0.08a 0.63±0.09ab 0.33±0.04b
NF-κB/GAPDH 1.13±0.14b 1.66±0.13a 1.37±0.10b 1.27±0.15b
注:与CON组对比,aP < 0.05;与SAP组对比,bP < 0.05

A为各组大鼠血清IL-6水平的定量分析;B为代表性Western Blot法检测四组大鼠肠黏膜组织PARP-1、NF-κB蛋白的表达水平;C-D为肠黏膜组织PARP-1、NF-κB蛋白的定量分析;与CON组对比,aP < 0.05;与SAP组对比,bP < 0.05 图 4 血清IL-6水平及肠黏膜组织PARP-1、NF-κB表达 Fig 4 Serum IL-6 levels and expression of PARP-1, NF-κB in intestinal mucosa

CON组肠黏膜组织中PARP-1少量表达。SAP组PARP-1表达明显增多。SAP组及3-AB组肠黏膜组织PARP-1均表达较CON组明显增加,差异均有统计学意义(P < 0.05);3-AB组较SAP组表达减少,差异有统计学意义(P < 0.05),见表 3图 4BC

CON组肠黏膜组织中NF-κB p65少量表达。SAP组NF-κB p65表达明显增多。SAP组肠黏膜NF-κB p65表达明显较CON组增加,差异有统计学意义(P < 0.05);3-AB组较SAP组表达减少,差异有统计学意义(P < 0.05),见图 4BD

3 讨论

重症急性胰腺炎占急性胰腺炎总病例数的20%~30%,具有起病急、进展快、并发症多、病死率高的特点。SAP患者主要表现为胰腺坏死,部分可进展到全身炎症反应综合征(systemic inflammatory response syndrome, SIRS)和MODS,其病死率现约为15%[7]

重症急性胰腺炎发病时炎症细胞激活,引发炎症级联瀑布反应,导致SIRS发生[8]。随着炎症反应的不断扩大,大量释放的炎症因子如IL-2、IL-6可损伤胰腺以外的远隔器官[9],如肺脏、肝脏、肾脏、肠道等重要器官,最终演变为MODS,导致患者死亡。SAP合并肠黏膜损伤是一个不同机制相互影响、相互作用的复杂的病理过程,可能与炎症介质激活、氧化应激和肠道缺血等因素有关。小肠作为远隔受损器官之一,SAP时微循环障碍导致液体聚集在第三间隙,机体开始出现血容量减少,导致全身血流重新分布,内脏血管尤其是肠管血供急剧下降,呈低灌注状态,肠黏膜组织缺血缺氧,是导致肠黏膜屏障损伤的主要原因[10-12]。肠黏膜屏障包括机械屏障、免疫屏障、化学屏障等,SAP时以机械屏障损伤最明显,其主要由肠黏膜上皮细胞和细胞间连接构成,细胞间连接包括紧密连接、粘附连接、缝隙连接等,肠上皮细胞间连接的主要蛋白有Occludin、ZO-1、Claudin等,其中Occludin蛋白是主要功能蛋白之一,对维持正常肠黏膜屏障起着重要作用[13-15]。细菌易位是肠道细菌穿过肠黏膜屏障进入各器官系统,是胰腺发生重复坏死,脓毒症的主要原因,是SAP患者死亡的第二高峰期[16-19]

PARP属于真核细胞中的多功能蛋白修饰酶家族,主要参与细胞内DNA复制修复、转录调控、信号转导,其中PARP-1活性最强,约占家族总活性90%以上。近期研究显示其在胰腺炎、脓毒症、复合伤等疾病的免疫应答中也起着重要作用。在重症感染时,PARP-1过度表达,可调节多效性转录调控因子NF-κB进入细胞核内,与NF-κB位点结合,促进下游细胞因子IL-6、TNF-α的释放,细胞因子进一步激活NF-κB,形成正反馈,释放大量炎症因子,形成细胞因子网络级联瀑布反应,导致肠道黏膜屏障损伤、菌群异位,进一步导致全身炎症反应及多器官功能障碍,甚至死亡[20-23]。已有研究表明,在重症急性胰腺炎大鼠模型中,肾上腺中PARP-1含量明显升高,PARP-1抑制剂3-AB可显著减轻重症胰腺炎肾上腺组织损伤[24-27]。另有研究表明,在重症急性胰腺炎大鼠模型中,肺组织中PARP-1含量明显升高,PARP-1抑制剂3-AB可显著减轻重症胰腺炎肺组织损伤[28-30]。但对SAP肠黏膜屏障的影响还有待深入研究及讨论。本研究结果显示,PARP-1及NF-κB在SAP大鼠肠组织中显著增加, 肠黏膜Occludin蛋白表达明显减少;PARP-1抑制剂3-AB可显著减轻胰腺及肠组织损伤,降低血清淀粉酶水平。

SAP时释放的大量促炎因子是肠黏膜屏障损伤的主要原因,IL-6等促炎因子激活中性粒细胞,引起肠黏膜上皮细胞直接受损、变形及坏死,同时促炎症因子促进氧化物质及蛋白水解酶释放,加重肠黏膜炎症反应,细胞紧密连接损伤,导致肠黏膜屏障及通透性增加[31-33]。本研究结果显示,SAP大鼠血清中IL-6水平较高,PARP-1抑制剂3-AB可显著降低血清IL-6水平。

综上所述,SAP大鼠肠组织PARP-1高表达在肠黏膜屏障功能损害及病情进展中起着重要作用,抑制PARP-1表达对SAP肠黏膜屏障损伤有保护作用,其作用机制可能与通过抑制NF-κB信号通路、增加肠黏膜Occludin蛋白表达有关,为预防和治疗SAP肠黏膜屏障损伤提供可施行的治疗方案。

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