Effect of ischemic preconditioning and postconditioning on liver regeneration in prepubertal rats

To Protect Fatty Livers from Ischemia Reperfusion Injury: Role of Ischemic Postconditioning

BACKGROUND

The benefit of ischemic postconditioning (IPostC) might be the throttled inflow following cold ischemia. The current study investigated advantage and mechanisms of IPostC in healthy and fatty rat livers.

METHODS

Male SD rats received a high-fat diet to induce fatty livers. Isolated liver perfusion was performed after 24 h ischemia at 4 °C as well as in vivo experiments after 90 min warm ischemia. The so-called follow-up perfusions served to investigate the hypothesis that medium from IPostC experiments is less harmful. Lactate dehydrogenase (LDH), transaminases, different cytokines, and gene expressions, respectively, were measured.

RESULTS

Fatty livers showed histologically mild inflammation and moderate to severe fat storage. IPostC reduced LDH and TXB₂ in healthy and fatty livers and increased bile flow. LDH, TNF-α, and IL-6 levels in serum decreased after warm ischemia + IPostC. The gene expressions of Tnf, IL-6, Ccl2, and Ripk3 were downregulated in vivo after IPostC.

CONCLUSIONS

IPostC showed protective effects after ischemia in situ and in vivo in healthy and fatty livers. Restricted cyclic inflow was an important mechanism and further suggested involvement of necroptosis. IPostC represents a promising and easy intervention to improve outcomes after transplantation.

Ischemic Postconditioning (IPostC) Protects Fibrotic and Cirrhotic Rat Livers after Warm Ischemia

BACKGROUND

Decreased organ function following liver resection is a major clinical issue. The practical method of ischemic postconditioning (IPostC) has been studied in heart diseases, but no data exist regarding fibrotic livers.

AIMS

We aimed to determine whether IPostC could protect healthy, fibrotic, and cirrhotic livers from ischemia reperfusion injury (IRI).

METHODS

Fibrosis was induced in male SD rats using bile duct ligation (BDL, 4 weeks), and cirrhosis was induced using thioacetamide (TAA, 18 weeks). Fibrosis and cirrhosis were histologically confirmed using HE and EvG staining. For healthy, fibrotic, and cirrhotic livers, isolated liver perfusion with 90 min of warm ischemia was performed in three groups (each with n=8): control, IPostC 8x20 sec, and IPostC 4x60 sec. additionally, healthy livers were investigated during a follow-up study. Lactate dehydrogenase (LDH) and thromboxane B₂ (TXB₂) in the perfusate, as well as bile flow (healthy/TAA) and portal perfusion pressure, were measured.

RESULTS

LDH and TXB₂ were reduced, and bile flow was increased by IPostC, mainly in total and in the late phase of reperfusion. The follow-up study showed that the perfusate derived from a postconditioned group had much less damaging potential than perfusate derived from the nonpostconditioned group.

CONCLUSION

IPostC following warm ischemia protects healthy, fibrotic, and cirrhotic livers against IRI. Reduced efflux of TXB₂ is one possible mechanism for this effect of IPostC and increases sinusoidal microcirculation. These findings may help to improve organ function and recovery of patients after liver resection.

Ischemic postconditioning decreases iNOS gene expression but ischemic preconditioning ameliorates histological injury in a swine model of extended liver resection

Background

Both pre- and postconditioning have been shown to protect the liver parenchyma from ischemia/reperfusion (I/R) injury during hepatectomy by altering the production of NO. However, to date there is no study to compare their effect on the inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) gene expression, who are the main modulators in the pathway of NO during the acute phase of I/R injury.

Methods

We designed a prospective experimental cohort comprising of three groups (sham group-SG, preconditioning-PrG and postconditioning group-PoG) and consisting of 10 animals per group. All animals underwent extended hepatectomy (70%) under prolonged warm ischemia either after preconditioning or followed by postconditioning or without any protective maneuver (SG). Following reperfusion blood samples and liver biopsies were obtained at the start of reperfusion (0 hours), at 6 and 12 hours post reperfusion. iNOS and eNOS gene expression was assessed on liver tissue by polymerase chain reaction (PCR); in addition, the extent of hepatocellular injury was histologically assessed.

Results

At the beginning of reperfusion iNOS expression was significantly reduced in the PoG in comparison to the SG (Kruskal-Wallis test, P=0.012; Mann-Whitney U test, P<0.0005 Bonferroni correction) and continued to remain at low levels until 6 hours post reperfusion (Kruskal-Wallis test, P=0.01; Mann-Whitney U test, P<0.0005-Bonferroni correction) This difference was eliminated by 12 hours. No significant differences were found in the expression of eNOS between groups and within time measurements. Aspartate aminotransferase (AST) and Alkaline phosphatase (ALP) were found increased at the start of reperfusion; their levels continued to increase by 6 hours in all groups, however only in the PoG the increase attended statistical significance at 12 hours after reperfusion. ALT levels presented only minor alterations during the course of reperfusion. The PrG was found to have more intense hepatocellular injury at the start of reperfusion than the PoG however, that appeared to gradually settle by 12 hours in contrast to PoG where the hepatocellular injury continued to deteriorate.

Conclusions

PoG appeared to decrease iNOS overexpression more effectively than PrG in comparison to animals who have undergone no protective maneuver (SG). However, PrG was more effective than PoG in ameliorating the hepatocellular injury observed at 12 hours after the ischemic insult.

Gene Expression Profiling in Ischemic Postconditioning to Alleviate Mouse Liver Ischemia/Reperfusion Injury

Ischemic postconditioning (IPO) attenuates hepatic ischemia/reperfusion (I/R) injury. However, little is known about the underlying biological pathophysiology, which could be, at least in part, informed by exploring the transcriptomic changes using next-generation RNA sequencing (RNA-Seq). In this study, 18 mice (C57BL/6) were involved and randomly assigned to three groups: normal (n=6), I/R (n=6, subjected to 70% hepatic I/R), and IR+IPO (n=6, applying IPO to mice with I/R injury). We randomly selected 3 mice per group and extracted their liver tissues for next-generation RNA-Seq. We performed a bioinformatics analysis for two comparisons: normal vs. I/R and I/R vs. IR+IPO. From the analysis, 2416 differentially expressed genes (DEGs) were identified (p < 0.05 and fold change ≥ 1.5). Gene ontology (GO) analysis revealed that these genes were mainly related to cellular metabolic processes, nucleic acids and protein binding processes. The enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways for the DEGs were the mitogen-activated protein kinase (MAPK), IL-17 signalling pathway, regulating pluripotency of stem cells, and insulin resistance pathway. Validation of 12 selected DEGs by qRT-PCR showed that Cyr61, Atf3, Nr4a1, Gdf15, Osgin1, Egr1, Epha2, Dusp1, Dusp6, Gadd45a and Gadd45b were significantly amplified. Finally, a protein-protein interaction (PPI) network constructed to determine interactions of these 11 DEGs. In summary, by exploring gene expression profiling in regard to hepatic I/R and IPO using next-generation RNA-Seq, we suggested a few progression-related genes and pathways, providing some clues for future experimental research.

Beyond Preconditioning: Postconditioning as an Alternative Technique in the Prevention of Liver Ischemia-Reperfusion Injury

Liver ischemia/reperfusion injury may significantly compromise hepatic postoperative function. Various hepatoprotective methods have been improvised, aiming at attenuating IR injury. With ischemic preconditioning (IPC), the liver is conditioned with a brief ischemic period followed by reperfusion, prior to sustained ischemia. Ischemic postconditioning (IPostC), consisting of intermittent sequential interruptions of blood flow in the early phase of reperfusion, seems to be a more feasible alternative than IPC, since the onset of reperfusion is more predictable. Regarding the potential mechanisms involved, it has been postulated that the slow intermittent oxygenation through controlled reperfusion decreases the burst production of oxygen free radicals, increases antioxidant activity, suppresses neutrophil accumulation, and modulates the apoptotic cascade. Additionally, favorable effects on mitochondrial ultrastructure and function, and upregulation of the cytoprotective properties of nitric oxide, leading to preservation of sinusoidal structure and maintenance of blood flow through the hepatic circulation could also underlie the protection afforded by postconditioning. Clinical studies are required to show whether biochemical and histological improvements afforded by the reperfusion/reocclusion cycles of postconditioning during early reperfusion can be translated to a substantial clinical benefit in liver resection and transplantation settings or to highlight more aspects of its molecular mechanisms.