Background. Extended cold preservation contributes to ischemia-reperfusion injury (IRI), which impairs graft function and leads to poor clinical outcomes. Serelaxin (SER), a recombinant form of a human hormone relaxin, promotes cardioprotection and ameliorates IRI in experimental cardiac models. Phase III clinical trials are underway to evaluate the efficacy of SER in acute heart failure. No data exists as to whether/how SER may influence innate immune activation and inflammatory responses in liver transplant recipients. We have recently shown that heme oxygenase-1 (HO-1) activated macrophage Notch1/Hes1/Stat3/Akt signaling is instrumental in liver resistance against IRI by reprogramming macrophages toward the M2 phenotype and inducing anti-apoptotic proteins. Aim. This study was designed to determine the effects of SER upon IRI pathology in mouse orthotopic liver transplantation (OLT) and in vitro in bone marrow-derived macrophage (BMM) cultures. Methods. Male C57BL/6 mouse livers, preserved for 20h at 4[deg] in UW solution, were transplanted orthotopically to syngeneic mice (C57BL/6). A SER bolus was given at reperfusion (5ug/kg via portal vein) and OLT were harvested at 6h of reperfusion. The effects of SER (5[mu]g/ml) were also studied in LPS (100ng/ml) or IL-4 (10ng/ml) stimulated BMM cultures.

Results. Donor liver conditioning with SER (at time of reperfusion) significantly decreased sALT levels in OLT recipients (3,499±668 vs. 7,125±1018 IU/L; n=5/gr; p<0.05); and ameliorated IR-mediated hepatocellular damage, assessed by histology (Suzuki's score: 1.8±0.5 vs. 5.0±0.8; n=5/gr; p<0.05) as compared with controls. In LPS-stimulated BMM cultures, SER increased protein levels of Notch1, Hes1, p-Stat3, Arg-1, p-Akt, Bcl-xL, Bcl-2 and decreased p-IkBa (Western analyses). In parallel, SER decreased mRNA levels coding for IL-1β, CXCL-10, MCP1, CCL-5 and IL-12 while Arg-1 expression sharply increased after LPS stimulation (RT-PCR, p<0.05). Consistently, after IL-4 stimulation, SER increased protein levels of Notch1, Hes1, p-Stat3 and mRNA levels of Arg-1, CD163, CCL-24, IL-10, c-Myc (p<0.05). However, SER did not affect HO-1 expression in LPS or IL-4 stimulated BMM cultures. Conclusion. This study is the first to document the efficacy of SER against hepatic IRI in mouse orthotopic liver transplantation. SER attenuated macrophage activation and reduced IR-hepatocellular damage by activating Notch1 signaling independent from anti-oxidant HO-1 pathway.

CITATION INFORMATION: Kageyama S, Nakamura K, Busuttil R, Kupiec-Weglinski J. Serelaxin Decreases the Severity of Cold Ischemia-Reperfusion Injury After Liver Transplantation in Mice. Am J Transplant. 2016;16 (suppl 3).

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