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.