microRNAs & liver disease
microRNAs in liver function and disease
Over the past years, evidence has emerged that microRNAs involved in the regulation of cholesterol and lipid metabolism in the liver may contribute to the development of metabolic disturbances and cardiovascular disease.
MicroRNA-122 (miR-122) was one of the first examples of a tissue-specific microRNA. It is highly expressed in liver, where it constitutes 70% of the total microRNA pool. This means that circulating miR-122 is almost exclusively derived from liver with very little interference by other tissues. MiR-122 regulates a number of genes associated to cholesterol and FA metabolism.
monitoring hepatotoxicity – gold-standard
Due to the lack of specific drug induced liver injury (DILI) biomarkers, DILI is monitored and diagnosed based on general liver injury serum biomarkers, such as alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), and total bilirubin (TBL). ALT, AST, and ALP are all intracellular enzymes, which when detected in serum can indicate injury to hepatocytes or biliary cells. An increase in serum TBL on the other hand reflects liver dysfunction, but while being liver- specific it is relatively insensitive and subsequently appears later along the disease progression. ALT, AST, and ALP are not liver- specific and extrahepatic conditions such as myocardial damage, skeletal muscle diseases, hyperthyroidism, and bone diseases are associated with increased ALT, AST, or ALP (1).
While disease-specific biomarkers have found their application in clinical drug development, in particular in oncology, and have been accepted by health authorities in a number of cases, biomarkers for organ toxicity were only very recently endorsed by FDA and European Medicines Agency (EMEA) for use in preclinical toxicity studies (2).
Key points for the use of microRNAs as liver function biomarkers
- highly sensitive and specific blood-based biomarker to assess liver function.
- Surrogate marker for hepatic vein pressure gradient.
- Circulating miR-122 is at least as informative as alanine aminotransferase (ALT) in acetaminophen (APAP)-induced liver injury.
- High tissue-specificity of serum miR-122 is useful to discriminate between hepatic and non-hepatic serum ALT elevations (e.g. muscular toxicity).
- Pre-clinical data suggest serum levels of miR-122 increase earlier than ALT levels.
- Levels of miR-122 are significantly higher in acute liver injury (ALI) patients but not chronic kidney disease (CKD) patients.
MicroRNAs are not independent of other liver function parameters such as ALT and AST. However, they are more sensitive and specific. Associations to liver hypertension and liver fibrosis have been published for these microRNA biomarkers.
Circulating microRNAs can be quantified in serum and plasma samples as well as in liquid biopsy using quantitative PCR. This gold-standard method is reliable and can undergo technical validation. However, in order to be successful, a well-characterized and standardized protocol must be used. TAmiRNA has developed a robust workflow and offers qPCR services for circulating microRNA analysis.
Numerous studies have by now validated the regulation of microRNAs in liver function and disease:
- miR-122-5p is highly enriched in the liver tissue and affects various genes involved in hepatic cholesterol and lipid metabolism, thereby having a central role in maintaining liver homeostasis. MiR-122-5p exhibit dose- and exposure duration-dependent changes in the plasma that correlate with ALT serum levels and with histopathological changes during liver degeneration (4,5).
- miR-151a-5p is significantly downregulated in patients suffering from postoperative liver dysfunction (LD) after liver resection (6).
- miR-192-5p most available data on miRNAs in drug-induced liver injury (DILI) are related to acetaminophen-induced acute liver failure. The levels of miR-192-5p and miR-122-5p are decreased in the livers of mice administered with acetaminophen. The mechanisms causing a decrease in levels of miR-122-5p and miR-192-5p after DILI are not clear, but the most probable explanation is that hepatocyte damage releases these miRNAs into the circulation (7).
The hepatomiR® panel allow to analyze three distinct liver specific microRNAs. A software algorithm converts the plasma signal of the three miRNAs into a score between 0 and 1, which reflects liver function. This score is easily interpretable and actionable, because we have determined cut-offs to stratify patients into risk groups