Barking up the wrong tree: MicroRNAs in bile as markers for biliary complications

Bile Composition as a Diagnostic and Prognostic Tool in Liver Transplantation

Bile secretion and composition reflects the functional status of hepatocytes and cholangiocytes. Bile composition can have a role in the assessment of donor grafts before implantation in the recipient. In addition, changes in bile composition after liver transplantation can serve as a diagnostic and prognostic tool to predict posttransplant complications, such as primary nonfunction, acute cellular rejection, or nonanastomotic biliary strictures. With the popularization of liver machine perfusion preservation in the clinical setting, there is a revisited interest in biliary biomarkers to assess graft viability before implantation. This review discusses current literature on biliary biomarkers that could predict or assess liver graft and bile duct viability. Bile composition offers an exciting and novel perspective in the search for reliable hepatocyte and cholangiocyte viability biomarkers.

Using next-generation sequencing of microRNAs to identify host and/or pathogen nucleic acid signatures in samples from children with biliary atresia - a pilot study

Biliary atresia (BA) is a progressive disease affecting infants resulting in inflammatory obliteration and fibrosis of the extra- and intra-hepatic biliary tree. BA may be grouped into type 1 isolated; type 2 syndromic, where other congenital malformations may be present; type 3 cystic BA, where there is cyst formation within an otherwise obliterated biliary tree; and cytomegalovirus-associated BA. The cause of BA is unclear, with immune dysregulation, inflammation and infection, particularly with cytomegalovirus (CMV), all implicated. In this study a total of 50/67 samples were tested for CMV DNA using quantitative real-time PCR. Ten liver tissue and 8 bile samples from 10 patients representing the range of BA types were also analysed by next-generation sequencing. CMV DNA was found in 8/50 (16 %) patients and a total of 265 differentially expressed microRNAs were identified. No statistically significant differences between the various types of BA were found. However, differences were identified in the expression patterns of 110 microRNAs in bile and liver tissue samples (P<0.05). A small number of bacterial and viral sequences were found, although their relevance to BA remains to be determined. No direct evidence of viral causes of BA were found, although clear evidence of microRNAs associated with hepatocyte and cholangiocyte differentiation together with fibrosis and inflammation were identified. These include miR-30 and the miR-23 cluster (liver and bile duct development) and miR-29, miR-483, miR-181, miR-199 and miR-200 (inflammation and fibrosis).

Polarized release of hepatic microRNAs into bile and serum in response to cellular injury and impaired liver function

BACKGROUND & AIMS

Extracellular microRNAs (miRNAs) in serum and bile are currently under intense investigation for biomarker purposes in liver disease. However, the directions and pathways by which miRNAs are released from hepatic cells remains largely unknown. Here, we investigated the release of hepatocyte and cholangiocyte-derived miRNAs (HDmiRs and CDmiRs) into blood and bile during various (patho)physiological hepatic conditions.

METHODS

MiRNA release was analysed using longitudinally collected tissue and paired bile and serum samples (n = 124) that were obtained from liver transplant recipients during follow-up.

RESULTS

Cell-type specificity of HDmiRs and CDmiRs was confirmed in liver and common bile duct biopsies (P < 0.001). Analysis of paired bile and serum samples showed up to 20-times higher miRNA-levels in bile compared to serum (P < 0.0001). Fractionation of bile showed the majority of miRNAs being present in the unpelletable supernatant, where protein conjunctions protect miRNAs against degradation (P < 0.0001). During episodes of liver injury and histologically proven rejection in liver transplant recipients, relative HDmiR-levels in bile decreased while its levels in serum increased (P ≤ 0.015). Simultaneously, relative CDmiR-levels in bile significantly increased, while their levels in serum decreased. Related to liver excretory function, a strong positive correlation was observed between HDmiR-122 levels and bilirubin excretion into bile (R = 0.694, P < 0.0001), whereas CDmiRs showed an inverse correlation (P < 0.05).

CONCLUSION

During impaired excretory function and injury, the liver shows polarized release of extracellular HDmiRs and CDmiRs. This sheds new light on the biology of hepatic miRNA release which is relevant for the interpretation of hepatic miRNAs as biomarkers.

The ins and outs of microRNAs as biomarkers in liver disease and transplantation

Ongoing research is being conducted in the field of transplantation to discover novel, noninvasive biomarkers for assessment of graft quality before transplantation and monitoring of graft injury after transplantation. MicroRNAs (miRNAs) are among the most promising in this field. MiRNAs are small noncoding RNAs that function as important regulators of gene expression in response to cellular stress and disease. An advantage that makes miRNAs attractive candidates for biomarker research is their fast release from cells in response to stress and injury, which can occur via different routes. In the context of liver transplantation (LT), noninvasive measurement and stability of extracellular miRNAs in blood, bile, and graft perfusates has been linked to cell-type specific injury and early graft outcome following LT. Furthermore, specific intrahepatic miRNA expression patterns have been associated with graft survival and recurrent disease, like hepatitis C virus-related fibrosis and hepatocellular carcinoma. Therefore, miRNAs with strong predictive value and high sensitivity and specificity might be successfully applied to assess hepatic injury and to diagnose (recurrent) liver disease before, during and after LT. In this review, the current features and future prospects of miRNAs as biomarkers in and out of the liver are discussed.