Plasma microRNA, a potential biomarker for acute rejection after liver transplantation.

Background: Acute rejection (AR) of an organ transplant is a life-threatening complication. Currently, there are few diagnostic biomarkers suitable for clinical application. We aim to determine the potential of plasma microRNAs as biomarkers for AR.
Methods: Using rat orthotopic liver transplantation model and microarrays, we compared the difference in the spectrum and levels of microRNAs in both plasma and grafts between AR rats and control. AR-related plasma microRNAs were selected and validated using real-time quantification polymerase chain reaction. Plasma from AR rats with or without tacrolimus treatment was used for microRNA dynamic monitoring. To clarify the origin of AR-related plasma microRNAs, drug-induced liver damage rat model were performed and in situ hybridization was used to detect and localize the specific microRNA in allografts.
Results: We found that plasma miR-122, miR-192, and miR-146a was significantly up-regulated when AR occur (fold change>2; P<0.05) and the elevation could be repressed by immunosuppression. In liver injury rat model, up-regulated plasma miR-122 (fold change=22.126; P=0.002) and miR-192 (fold change=8.833; P<0.001) rather than miR-146a (fold change=1.181; P=0.594) were observed. Further study demonstrated that miR-146a was up-regulated by sixfold in microvesicles isolated from AR plasma, whereas miR-122 and miR-192 showed no distinct change. In situ hybridization revealed that the portal areas of the AR graft were brimming with lymphocytes, which showed highly intense staining for miR-146a.
Conclusions: Our study provides the global fingerprint of plasma microRNAs in AR rats and suggests that plasma miR-122 and miR-192 reflect liver injury, whereas miR-146a may associate with cellular rejection.