Mechanisms causing cholemic nephropathy

胆汁性肾病(CN)是一种严重的、通常是致命的几种肝脏疾病的并发症，目前还没有专门的治疗方法。在我们之前的工作中，我们使用了小鼠胆管结扎(BDL)作为CN的临床前模型。在MALDI-MSI和LC-MS/MS的支持下，我们使用活体成像技术观察了肾脏和肝脏的胆汁流量。我们发现，胆汁酸(BA)从肾小管腔重新吸收到近端肾小管上皮细胞(TEC)，在TEC中BA的增加伴随着细胞的死亡。BDL后3周及以后，肾小管周毛细血管受损，BA大量渗入肾间质，随后出现白细胞浸润和纤维化。由于TEC在其顶腔膜上表达BA摄取载体顶端钠依赖胆汁酸转运体(ASBT；Slc10a2)，我们使用系统可用的ASBT抑制剂AS0369来阻断BA的摄取。从活体影像、肾脏组织学、转录本以及尿液和血清生物标记物来看，这几乎完全预防了BDL术后6周内的肾脏损伤。然而，目前尚不清楚胆汁酸、胆红素或其他炎症介质是否会导致胆汁性肾病。为了制定治疗策略，澄清导致这种疾病的确切机制将是重要的。因此，本项目将澄清以下问题：胆汁酸和胆红素在胆汁性肾病中的作用是什么？在我们之前的工作中，我们已经获得了胆汁酸可能起到因果作用的证据，因为AS0369预防了胆汁性肾病。然而，AS0369降低了全身血液中胆汁酸和胆红素的浓度。为了确定因果关系，将使用干预措施来特定地修饰TEC(胆汁性肾病的靶细胞)中的胆汁酸或胆红素。胆汁酸亲水性的改变会改变胆汁性肾病吗？众所周知，相对亲水性胆汁酸的毒性比疏水性胆汁酸小，在肾脏组织中也是如此。如果胆汁酸是TEC细胞死亡事件的罪魁祸首(从而导致胆汁性肾病)，那么导致胆汁酸更亲水、更具保护性的光谱的干预措施应该会改善疾病。如果是这样的话，两种方法的结合--通过抑制ASBT来减少胆汁酸的重吸收和代谢调节以产生更亲水的胆汁酸光谱--可能会导致相加(或协同)的治疗效果。

Cholemic nephropathy (CN) is a severe, often fatal complication of several liver diseases and no specific treatment is currently available. In our previous work, we used bile duct ligation (BDL) in mice as a preclinical model of CN. We visualized bile flux in kidneys and livers using intravital imaging, supported by MALDI-MSI and LC-MS/MS. We showed that bile acids (BA) are reabsorbed from the renal tubular lumen into proximal renal tubular epithelial cells (TEC) and that BA enrichment in TEC is followed by cell death. At week 3 after BDL and later, damage of peritubular capillaries and massive leakage of BA into the renal interstitium were observed, followed by leukocyte infiltration and fibrosis. Since TEC express the apical sodium-dependent bile acid transporter (ASBT; Slc10a2), a BA uptake carrier, at their apical luminal membrane, we used the novel compound AS0369, a systemically bioavailable ASBT inhibitor, to block BA uptake. This almost completely prevented kidney injury up to 6 weeks after BDL, as evidenced by intravital imaging, kidney histology, transcriptomics, and urine and serum biomarkers. However, it remains currently unclear, if bile acids, bilirubin or other inflammatory mediators cause cholemic nephropathy. For the development of therapeutic strategies, it would be important to clarify the exact mechanism responsible for the disease. Therefore, the present project will clarify the following questions: What is the contribution of bile acids and bilirubin to cholemic nephropathy? In our previous work we have obtained evidence that bile acids may play a causal role, because AS0369 prevented cholemic nephropathy. However, AS0369 reduced both, systemic blood concentrations of bile acids and bilirubin. To establish a causal relationship, interventions to specifically modify either bile acids or bilirubin in TEC (the target cells of cholemic nephropathy) will be used. Does modification of hydrophilicity of bile acids modify cholemic nephropathy? It is well known that relatively hydrophilic bile acids are less toxic than hydrophobic bile acids also in kidney tissue. If bile acids are responsible for cell death events of TEC (and consequently for cholemic nephropathy), then interventions that lead to a more hydrophilic, ‘protective’ spectrum of bile acids should ameliorate the disease. If this is the case, the combination of both approaches – reducing bile acid reabsorption by ASBT inhibition and metabolic conditioning to generate a more hydrophilic bile acid spectrum – could lead to additive (or synergistic) therapeutic effects.