PURPOSE OF REVIEW: Hepatic ischemia-reperfusion injury (IRI), an inevitable event during liver transplantation, represents a major risk factor for the primary graft dysfunction as well as the development of acute and chronic rejection. Neutrophils, along macrophages are pivotal in the innate immune-driven liver IRI, whereas the effective neutrophil targeting therapies remain to be established. In this review, we summarize progress in our appreciation of the neutrophil biology and discuss neutrophil-based therapeutic perspectives. RECENT FINDINGS: New technological advances enable to accurately track neutrophil movements and help to understand molecular mechanisms in neutrophil function, such as selective recruitment to IR-stressed tissue, formation of neutrophil extracellular traps, or reverse migration into circulation. In addition to pro-inflammatory and tissue-destructive functions, immune regulatory and tissue-repairing phenotype associated with distinct neutrophil subsets, have been identified. SUMMARY: Newly recognized and therapeutically attractive neutrophil characteristics warrant comprehensive preclinical and clinical attention to target IRI in transplant recipients.

Introduction: Liver transplantation is the only viable treatment with a proven survival benefit for acute liver failure (ALF). Donor organ shortage is, however, a major hurdle; hence, alternative approaches that enable liver regeneration and target acute severe hepatocellular damage are necessary.Areas covered: This article sheds light on therapeutic targets for liver regeneration and considers their therapeutic potential. ALF following extensive hepatocyte damage and small-for-size syndrome (SFSS) are illuminated for the reader while the molecular mechanisms of liver regeneration are assessed in accordance with relevant therapeutic strategies. Furthermore, liver background parameters and predictive biomarkers that might associate with liver regeneration are reviewed.Expert opinion: There are established and novel experimental strategies for liver regeneration to prevent ALF resulting from SFSS. Granulocyte-colony stimulating factor (G-CSF) is a promising agent targeting liver regeneration after acute severe injury. Autophagy and hepatocyte senescence represent attractive new targets for liver regeneration in acute severe hepatic injury. Liver support strategies, including tissue engineering, constitute novel regenerative means; the success of this is dependent on stem cell research advances. However, there is no firm clinical evidence that these supportive strategies may alleviate hepatocellular damage until liver transplantation becomes available or successful self-liver regeneration occurs.

Purpose of review

Although organ transplantation has become the standard life-saving strategy for patients with end-stage organ failure and those with malignancies, effective and safe therapeutic strategies to combat allograft loss remain to be established. With the emerging evidence suggesting the critical role of innate immunity in the mechanism of allograft injury, we summarize the latest understanding of macrophage-neutrophil cross-communication and discuss therapeutic prospects of their targeting in transplant recipients.

Recent findings

Macrophages and neutrophils contribute to the pathogenesis of early peritransplant ischemia-reperfusion injury and subsequent allograft rejection immune cascade, primarily by exacerbating inflammatory response and tissue damage. Noteworthy, recent advances enabled to elucidate multifaceted functions of innate immune cells, which are not only deleterious but may also prove graft-protective. Indeed, the efficacy of macrophage polarizing regimens or macrophage-targeted migration have been recognized to create graft-protective local environment. Moreover, novel molecular mechanisms in the neutrophil function have been identified, such as neutrophil extracellular traps, tissue-repairing capability, crosstalk with macrophages and T cells as well as reverse migration into the circulation.

Summary

As efficient strategies to manage allograft rejection and improve transplant outcomes are lacking, newly discovered, and therapeutically attractive innate immune cell functions warrant comprehensive preclinical and clinical attention.

Purpose of review

Hepatic ischemia-reperfusion injury (IRI), an inevitable event during liver transplantation, represents a major risk factor for the primary graft dysfunction as well as the development of acute and chronic rejection. Neutrophils, along macrophages are pivotal in the innate immune-driven liver IRI, whereas the effective neutrophil targeting therapies remain to be established. In this review, we summarize progress in our appreciation of the neutrophil biology and discuss neutrophil-based therapeutic perspectives.

Recent findings

New technological advances enable to accurately track neutrophil movements and help to understand molecular mechanisms in neutrophil function, such as selective recruitment to IR-stressed tissue, formation of neutrophil extracellular traps, or reverse migration into circulation. In addition to pro-inflammatory and tissue-destructive functions, immune regulatory and tissue-repairing phenotype associated with distinct neutrophil subsets, have been identified.

Summary

Newly recognized and therapeutically attractive neutrophil characteristics warrant comprehensive preclinical and clinical attention to target IRI in transplant recipients.

Hepatic ischemia-reperfusion injury (IRI), a major risk factor for early allograft dysfunction (EAD) and acute or chronic graft rejection, contributes to donor organ shortage for life-saving orthotopic liver transplantation (OLT). The graft injury caused by local ischemia (warm and/or cold) leads to parenchymal cell death and release of danger-associated molecular patterns (DAMPs), followed by reperfusion-triggered production of reactive oxygen species (ROS), activation of inflammatory cells, hepatocellular damage and ultimate organ failure. Heme oxygenase 1 (HO-1), a heat shock protein-32 induced under IR-stress, is an essential component of the cytoprotective mechanism in stressed livers. HO-1 regulates anti-inflammatory responses and may be crucial in the pathogenesis of chronic diseases, such as arteriosclerosis, hypertension, diabetes and steatosis. An emerging area of study is macrophage-derived HO-1 and its pivotal intrahepatic homeostatic function played in IRI-OLT. Indeed, ectopic hepatic HO-1 overexpression activates intracellular SIRT1/autophagy axis to serve as a key cellular self-defense mechanism in both mouse and human OLT recipients. Recent translational studies in rodents and human liver transplant patients provide novel insights into HO-1 mediated cytoprotection against sterile hepatic inflammation. In this review, we summarize the current bench-to-bedside knowledge on HO-1 molecular signaling and discuss their future therapeutic potential to mitigate IRI in OLT.

Liver ischemia-reperfusion injury (IRI) represents a risk factor for early graft dysfunction and an obstacle to expanding donor pool in orthotopic liver transplantation (OLT). We have reported on the crucial role of macrophage Notch1 signaling in mouse warm hepatic IRI model. However, its clinical relevance or therapeutic potential remain unknown. Here, we used Serelaxin (SER), to verify Notch1 induction and putative hepatoprotective function in ischemia-reperfusion-stressed OLT. C57BL/6 mouse livers subjected to extended (18-hour) cold storage were transplanted to syngeneic recipients. SER treatment at reperfusion ameliorated IRI, improved post-OLT survival, decreased neutrophil/macrophage infiltration, and suppressed proinflammatory cytokine programs, while simultaneously increasing Notch intracellular domain (NICD) and hairy and enhancer of split 1 (Hes1) target genes. In bone marrow-derived macrophage cultures, SER suppressed proinflammatory while enhancing antiinflammatory gene expression concomitantly with increased NICD and Hes1. Hepatic biopsies from 21 adult primary liver transplant patients (2 hours postreperfusion) were divided into low-NICD (n = 11) and high-NICD (n = 10) expression groups (western blots). Consistent with our murine findings, human livers characterized by high NICD were relatively IRI resistant, as shown by serum alanine aminotransferase (ALT) levels at day 1 post-OLT. Our study documents the efficacy of SER-Notch1 signaling in mouse OLT and highlights the protective function of Notch1 in liver transplant patients.

Liver ischemia-reperfusion injury (IRI) represents a risk factor for early graft dysfunction and an obstacle to expanding donor pool in orthotopic liver transplantation (OLT). We have reported on the crucial role of macrophage Notch1 signaling in mouse warm hepatic IRI model. However, its clinical relevance or therapeutic potential remain unknown. Here, we used Serelaxin (SER), to verify Notch1 induction and putative hepatoprotective function in ischemia-reperfusion-stressed OLT. C57BL/6 mouse livers subjected to extended (18-hour) cold storage were transplanted to syngeneic recipients. SER treatment at reperfusion ameliorated IRI, improved post-OLT survival, decreased neutrophil/macrophage infiltration, and suppressed proinflammatory cytokine programs, while simultaneously increasing Notch intracellular domain (NICD) and hairy and enhancer of split 1 (Hes1) target genes. In bone marrow-derived macrophage cultures, SER suppressed proinflammatory while enhancing antiinflammatory gene expression concomitantly with increased NICD and Hes1. Hepatic biopsies from 21 adult primary liver transplant patients (2 hours postreperfusion) were divided into low-NICD (n = 11) and high-NICD (n = 10) expression groups (western blots). Consistent with our murine findings, human livers characterized by high NICD were relatively IRI resistant, as shown by serum alanine aminotransferase (ALT) levels at day 1 post-OLT. Our study documents the efficacy of SER-Notch1 signaling in mouse OLT and highlights the protective function of Notch1 in liver transplant patients.

Background

Bruton tyrosine kinase (Btk) is a central player in multiple signaling pathways of lymphoid and myeloid cells. Myeloid cells are crucial early effectors in organ ischemia-reperfusion (IR) injury. BTKB66 is a selective, irreversible inhibitor of Btk. In this study, we hypothesized that Btk inhibition would reduce hepatocellular injury in a murine model of liver warm hepatic IR.

Methods

First, BTKB66 was tested in in vitro models of lipopolysaccharide-mediated neutrophil and macrophage activation. Then, to assess its efficacy in vivo, BTKB66 was administered orally to mice for 7 days before subjecting them to 90 minutes of warm hepatic ischemia followed by reperfusion for 6 or 24 hours. Clinical and pathologic features in the livers, including AST, ALT, and a panel of cytokines and chemokines, were examined.

Results

BTKB66 potently inhibited lipopolysaccharide-mediated activation of bone marrow-derived neutrophils and macrophages in vitro. It also reduced the severity of IR injury as determined by AST and ALT levels, as well as immune cell infiltrates. BTKB66 significantly decreased hepatic markers of sterile inflammation, such as C-X-C motif chemokine 1, C-X-C motif chemokine 2, and C-X-C motif chemokine 10, in parallel with depression of serum markers of the myeloid cell activation, such as CCL5, CCL11, and C-X-C motif chemokine 5.

Conclusions

BTKB66 treatment ameliorated hepatocellular injury in a well-established model of liver partial warm ischemia and in situ reperfusion. These findings confirm that neutrophil recruitment and activation play an essential role in IR stress, and that targeting Btk activity may provide a useful approach for preventing hepatocellular damage and improving outcomes in liver transplantation.

Background and aims

Environmentally triggered chronic liver inflammation can cause collagen deposits, whereas early stages of fibrosis without any specific symptoms could hardly be detectable. We hypothesized that some of the human donor grafts in clinical liver transplantation (LT) might possess unrecognizable fibrosis, affecting their susceptibility to LT-induced stress and hepatocellular damage. This retrospective study aimed to assess the impact of occult hepatic fibrosis on clinical LT outcomes.

Approach and results

Human (194) donor liver biopsies were stained for collagen with Sirius red, and positive areas (Sirius red-positive area; SRA) were measured. The body mass index, aspartate aminotransferase/alanine aminotransferase ratio, diabetes score was calculated using 962 cases of the donor data at the procurement. LT outcomes, including ischemia-reperfusion injury (IRI), early allograft dysfunction (EAD), and survival rates, were analyzed according to SRA and BARD scores. With the median SRA in 194 grafts of 9.4%, grafts were classified into low-SRA (<15%; n = 140) and high-SRA (≥15%; n = 54) groups. Grafts with high SRA suffered from higher rates of IRI and EAD (P < 0.05) as compared to those with low SRA. Interestingly, high SRA was identified as an independent risk factor for EAD and positively correlated with the donor BARD score. When comparing low-BARD (n = 692) with high-BARD (n = 270) grafts in the same period, those with high BARD showed significantly higher post-LT transaminase levels and higher rates of IRI and EAD.

Conclusions

These findings from the largest clinical study cohort to date document the essential role of occult collagen deposition in donor livers on LT outcomes. High-SRA and donor BARD scores correlated with an increased incidence of hepatic IRI and EAD in LT recipients. This study provides the rationale for in-depth and prospective assessment of occult fibrosis for refined personalized LT management.