Published online Mar 14, 2015. doi: 10.3748/wjg.v21.i10.2937
Peer-review started: July 4, 2014
First decision: July 21, 2014
Revised: August 9, 2014
Accepted: November 7, 2014
Article in press: November 11, 2014
Published online: March 14, 2015
AIM: To investigate the efficacy and molecular mechanisms of induced heme oxygenase (HO)-1 in protecting liver from warm ischemia/reperfusion (I/R) injury.
METHODS: Partial warm ischemia was produced in the left and middle hepatic lobes of SD rats for 75 min, followed by 6 h of reperfusion. Rats were treated with saline, cobalt protoporphyrin (CoPP) or zinc protoporphyrin (ZnPP) at 24 h prior to the ischemia insult. Blood and samples of ischemic lobes subjected to ischemia were collected at 6 h after reperfusion. Serum transaminases level, plasma lactate dehydrogenase and myeloperoxidase activity in liver were measured. Liver histological injury and inflammatory cell infiltration were evaluated by tissue section and liver immunohistochemical analysis. We used quantitative reverse transcription polymerase chain reaction to analyze liver expression of inflammatory cytokines and chemokines. The cell lysates were subjected to immunoprecipitation with anti-Toll-IL-1R-containing adaptor inducing interferon-β (TRIF) and anti-myeloid differentiation factor 88 (MyD88), and then the immunoprecipitates were analyzed by SDS-PAGE and immunoblotted with the indicated antibodies.
RESULTS: HO-1 protected livers from I/R injury, as evidenced by diminished liver enzymes and well-preserved tissue architecture. In comparison with ZnPP livers 6 h after surgery, CoPP treatment livers showed a significant increase inflammatory cell infiltration of lymphocytes, plasma cells, neutrophils and macrophages. The Toll-like receptor (TLR)-4 and TANK binding kinase 1 protein levels of rats treated with CoPP significantly reduced in TRIF-immunoprecipitated complex, as compared with ZnPP treatment. In addition, pretreatment with CoPP reduced the expression levels of TLR2, TLR4, IL-1R-associated kinase (IRAK)-1 and tumor necrosis factor receptor-associated factor 6 in MyD88-immunoprecipitated complex. The inflammatory cytokines and chemokines mRNA expression rapidly decreased in CoPP-pretreated liver, compared with the ZnPP-treated group. However, the expression of negative regulators Toll-interacting protein, suppressor of cytokine signaling-1, IRAK-M and Src homology 2 domain-containing inositol-5-phosphatase-1 in CoPP treatment rats were markedly up-regulated as compared with ZnPP-treated rats.
CONCLUSION: HO-1 protects liver against I/R injury by inhibiting TLR2/TLR4-triggered MyD88- and TRIF-dependent signaling pathways and increasing expression of negative regulators of TLR signaling in rats.
Core tip: Heme oxygenase (HO)-1, a rate-limiting enzyme in heme degradation, has been shown to provide cytoprotection in various tissue and organ injury models. There is evidence suggesting that augmented Toll-like receptor (TLR) reactivity contributes to the development of heightened systemic inflammation following severe liver injury. In this study, by inducing the expression of HO-1 in a rat liver ischemia/reperfusion injury model, we demonstrated that HO-1 suppresses activation of the TLR2/TLR4-triggered myeloid differentiation factor 88 dependent pathway and promotes expression of negative regulators of TLR signaling.