Prolonged Cold Ischemia Does Not Trigger Lethal Rejection or Accelerate the Acute Rejection in Two Allogeneic Rat Liver Transplantation Models

CD47 blockade alleviates acute rejection of allogeneic mouse liver transplantation by reducing ischemia/reperfusion injury

Despite advances in immunosuppressive therapies, acute rejection response is still a serious concern especially in the early phase after liver transplantation. This study aimed to evaluate whether blocking the TSP1-CD47 signaling pathway could attenuate the acute rejection after liver transplantation. An allogeneic mouse orthotopic liver transplantation model (Balb/c→C3H) with prolonged cold ischemic phase was used to induce severe IRI and lethal acute rejection. CD47mAb or isotype matched-control IgG_2a was administered to donor liver during graft perfusion. Recipients were sacrificed at 1d, 3d, 5d and 7d after reperfusion. Blood samples were collected to evaluate serum alanine aminotransferase, total bilirubin, HMGB-1,TNF-α, IL-2 and INF-γ level. Flow cytometric analysis was used to detect the strength of innate and adaptive immune response. Liver tissue was obtained for HE, TUNEL staining and F4/80 immumohistochemical staining. Moreover, we conducted a mixed lymphocyte reaction treated with IgG_2a or CD47mAb. Mice in CD47mAb-treated group demonstrated improved survival and significantly lower increase in Suzuki score, apoptosis index, acute rejection index, serum alanine aminotransferase, total bilirubin, HMGB-1, TNF-α, IL-2, INF-γ level and the degree of Kupffer cells' activation especially in the early phase of acute rejection. In addition, Pearson's correlation analysis confirmed significant correlation between Suzuki score/ALT and acute rejection index. The in vitro inhibition assay showed that CD47 blockade couldn't directly inhibit recipient lymphocyte proliferation. Based on the evidence that TSP1-CD47 signaling blockade with CD47mAb could alleviate acute rejection by reducing the extent of IRI after liver transplantation indirectly, this study provided a basis for new interventions and management methods to support better transplant outcomes.

Efficacy of ursodeoxycholic acid as an adjuvant treatment to prevent acute cellular rejection after liver transplantation: a meta-analysis of randomized controlled trials

BACKGROUND

Acute cellular rejection (ACR) after liver transplantation (LT) is one of the most common problems faced by transplant recipients in spite of advances in immunosuppressive therapy. Recently, clinical trials reported that ursodeoxycholic acid (UDCA) reduced the incidence of ACR significantly. However, others have shown contradictory conclusion. Therefore, we performed a meta-analysis of rigorous randomized controlled trials (RCTs) to determine the efficacy of UDCA in reducing ACR after LT.

DATA SOURCES

All RCTs that evaluated efficacy of UDCA as an adjuvant treatment to prevent ACR after LT were searched from PubMed/MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, ScienceDirect databases and Web of Science (from January 1981 to March 2012). There was no language limitation in these searches. Relevant abstracts of international meetings were also searched. References of each included study were searched manually.

RESULTS

A total of 234 patients from four high-quality RCTs (Jadad score 4 to 5) were included in this meta-analysis. Prophylactic use of UDCA did not decrease the incidence of ACR (RR: 0.94, 95% CI: 0.77-1.16, P>0.05), steroid-resistant rejection (RR: 0.77, 95% CI: 0.47-1.27, P>0.05) and the number of patients with the multiple episodes of ACR (RR: 0.60, 95% CI: 0.28-1.30, P>0.05). Different intervention programs (high-dose vs low-dose UDCA; early vs delayed UDCA treatment) also did not alter the outcomes.

CONCLUSIONS

UDCA, as an adjuvant treatment, was not able to prevent ACR and steroid-resistant rejection after LT. Further trials should be done to determine whether higher dose of UDCA will be beneficial.

Oxidation of HMGB1 causes attenuation of its pro-inflammatory activity and occurs during liver ischemia and reperfusion

High mobility group box 1 (HMGB1) is a nuclear transcription factor. Once HMGB1 is released by damaged cells or activated immune cells, it acts as danger molecule and triggers the inflammatory signaling cascade. Currently, evidence is accumulating that posttranslational modifications such as oxidation may modulate the pro-inflammatory potential of danger signals. We hypothesized that oxidation of HMGB1 may reduce its pro-inflammatory potential and could take place during prolonged ischemia and upon reperfusion.

Liver grafts were cold preserved for 24 h and flushed with saline in hourly intervals to collect the effluent. Liver grafts, cold-preserved for 6 h, were transplanted into syngeneic recipients to obtain serum and liver samples 24 h after initiation of reperfusion. Addition of the effluent to a macrophage culture induced the synthesis of tumor necrosis factor-alpha (TNF-α) and interleukin (IL)-6. The stimulatory activity of graft effluent was reduced after depletion of HMGB1 via immunoprecipitation. Oxidation of the effluent HMGB1 using H₂O₂ attenuated its stimulatory activity as well. Liver transplantation of cold preserved grafts caused HMGB1 translocation and release as determined by immunohistochemistry and ELISA-assay, respectively. Using Western blot with non-reducing conditions revealed the presence of oxidized HMGB1 in liver samples obtained after 12 h and in effluent samples after 16 h of cold preservation as well as in liver and serum samples obtained 24 h after reperfusion.

These observations confirm that post-translational oxidation of HMGB1 attenuates its pro-inflammatory activity. Oxidation of HMGB1 as induced during prolonged ischemia and by reoxygenation during reperfusion in vivo might also attenuate its pro-inflammatory activity. Our findings also call for future studies to investigate the mechanism of the inhibitory effect of oxidized HMGB1 on the pro-inflammatory potential.