肠源性促胰液素对肠衰竭致肝脏胆汁淤积大鼠肝功能的保护作用

Patients who accept long-term parenteral nutrition tend to suffer from liver injury. The mechanism for this injury has two possible explantations. The first possible reason is intrinsic toxic effects of parenteral nutrition. The second is the basic pathological condition of intestinal failure which includes infection, bacterial translocation, etc. Cholestasis is the lethal presentation of this kind of liver disease. Intesinal graft has been proved to be able to ameliorate the liver injury. Several phenomena suggest that the cause of liver injury is shortage of small bowel mass rather than parenteral nutrition. Firstly, pseudo-obstruction patients showed better tolerance to parenteral nutrition than short bowel syndrome patients. Secondly, patients who suffered from chronic graft dysfunction and complete intestinal obstruction after intestinal transplantation can tolerant parenteral nutrition better than pre-operation. In this latter setting, the enterohepatic circulation of bile acid is even absent. All these facts led us to speculate that sufficient small intestine mass is a protetive factor to liver and this effect is independent on its digestive and absorbing function. Considering secretin is an intestine-orignated stimulator of bile secretion by cholangiocyte, the hypothesis of this study is that secretin plays a key role in the protective effect of intestinal graft to the liver. Using a mouse cholestasis model based on short bowel syndrome and parenteral nutrition, we will investigate the promoting effect of shortage of small bowel mass to liver injury and describe the dynamic change of plasma secretin level. Afterward, small bowel transplantation was added to this model to demonstrate small intestine can ameliorate cholestasis. To investigate the importance of secretin pathway in this effect, a secretin receptor knockout mouse model will be used as transplant recipient.

因肠衰竭而接受长期肠外营养的患者容易发生肝损伤，这一损伤的机制有两种可能原因，一是肠外营养本身组成成分的毒性作用，二是患者的基础病即各种病因造成的肠衰竭及其感染等并发症。胆汁淤积症是这一肝损伤的重要表现形式。有研究报道临床小肠移植可以改善受损的肝功能。我们观察到假性肠梗阻患者比短肠患者可以更好地耐受肠外营养，小肠移植后移植物慢性失功并发完全性肠梗阻的患者也较术前更好耐受肠外营养，这些现象使我们推断小肠的吸收功能以外的某项功能是保护肝功能的因素。已知促胰液素对肝脏胆汁分泌具有刺激作用，考虑到小肠是促胰液素的重要来源，我们假设促胰液素途径参与了移植肠对肝脏的保护作用。本研究通过建立短肠综合征肝脏胆汁淤积症模型，阐述小肠组织缺乏对肝损伤的促进作用，在此模型上进行异位小肠移植，进而证实小肠本身可以保护肝脏功能。通过敲除促胰液素受体基因的小鼠作为移植受体，探讨促胰液素在这一保护作用中所起的作用。

临床观察研究发现，短肠综合征（Short bowel syndrome, SBS）患者肠衰竭相关性肝病（intestinal failure associated liver disease，IFALD）发生率显著低于慢性假性肠梗阻患者（Chronic intestinal pseudo-obstruction,CIPO），而两者均是长期接受PN支持的人群。结合本中心的临床观察，我们分析肠道来源的激素可能扮演者重要作用，其中肠源性的促胰液素（Secretin）最可能是直接产生效应的激素。..首先建立一种新型简易的自由活动大鼠长期静脉置管模型用于支持后续研究。其次，我们观察短肠综合征模型静脉血清Secretin水平的变化，验证SBS患者存在肠道源性Secretin衰竭这一假设。结果显示短肠模型大鼠术后血清Secretin水平显著降低，但能逐步代偿，于术后2周左右达代偿平衡；长期肠外营养禁食模型亦能逐渐降低Secretin水平，禁食1周左右降至最低水平。之后，比较SBS大鼠与假手术大鼠经长期TPN支持之后，生化指标及肝组织损伤程度的差异。结果发现SBS大鼠IFALD相关指标显著大于假手术组大鼠，SBS大鼠IFALD肝脏凋亡率显著高于假手术组大鼠。证实小肠器质是肝损伤的保护因素。最后，我们通过对SBS大鼠Secretin生理剂量的补充，探索其在IFALD的作用。结果显示短肠模型大鼠给予补充生理水平Secretin之后能显著降低IFALD损害程度；Secretin在IFALD中的保护作用与抑制肝细胞凋亡相关，具体机制有待于进一步研究。.本课题证实了器质性短肠综合征时存在肠源性secretin衰竭，并且实验结果提示小肠缺失加重肝脏损伤，外源性补充secretin可以改善肝脏损伤，为证实其确实通过secretin这一通路发生作用，我们增加后续试验用shRNA干扰secretin受体再次观察secretin是否显示保护作用。

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