Circulating microRNA-122 as a potential biomarker for liver injury.

Liver-specific microRNA-122 (miR-122) is involved in the replication of hepatitis C virus (HCV) and its potential as a target for antiviral intervention was recently assessed. However, the use of circulating miR-122 in the evaluation of liver function has never been reported. In the present study, changes of serum miRNA levels were first evaluated in acute human hepatotoxicity due to paraquat exposure. Serum samples were collected and analyzed using real-time reverse transcription PCR. The results showed a positive correlation between serum miR-122 and alanine aminotransferase, a clinical biomarker for liver function. Furthermore, serum miR-122 was assessed in patients with hepatitis B and hepatocarcinoma, resulting in distinct miR-122 profiles in these two closely related diseases. In addition to miR-122, another small RNA, U6 small nuclear RNA, was downregulated in hepatocarcinoma patients, suggesting its prognostic significance in this disease. Taken together, these lines of evidence indicate that serum miR-122 may provide a biomarker for diverse liver diseases and, more importantly, suggest that a combination of nucleic acid biomarkers may be used as a sensitive and specific index for discriminating closely related diseases.