AMP-Activated Protein Kinase as a Target for Preconditioning in Transplantation Medicine

Liver Graft Hypothermic Static and Oxygenated Perfusion (HOPE) Strategies: A Mitochondrial Crossroads

Marginal liver grafts, such as steatotic livers and those from cardiac death donors, are highly vulnerable to ischemia–reperfusion injury that occurs in the complex route of the graft from “harvest to revascularization”. Recently, several preservation methods have been developed to preserve liver grafts based on hypothermic static preservation and hypothermic oxygenated perfusion (HOPE) strategies, either combined or alone. However, their effects on mitochondrial functions and their relevance have not yet been fully investigated, especially if different preservation solutions/effluents are used. Ischemic liver graft damage is caused by oxygen deprivation conditions during cold storage that provoke alterations in mitochondrial integrity and function and energy metabolism breakdown. This review deals with the relevance of mitochondrial machinery in cold static preservation and how the mitochondrial respiration function through the accumulation of succinate at the end of cold ischemia is modulated by different preservation solutions such as IGL-2, HTK, and UW (gold-standard reference). IGL-2 increases mitochondrial integrity and function (ALDH2) when compared to UW and HTK. This mitochondrial protection by IGL-2 also extends to protective HOPE strategies when used as an effluent instead of Belzer MP. The transient oxygenation in HOPE sustains the mitochondrial machinery at basal levels and prevents, in part, the accumulation of energy metabolites such as succinate in contrast to those that occur in cold static preservation conditions. Additionally, several additives for combating oxygen deprivation and graft energy metabolism breakdown during hypothermic static preservation such as oxygen carriers, ozone, AMPK inducers, and mitochondrial UCP2 inhibitors, and whether they are or not to be combined with HOPE, are presented and discussed. Finally, we affirm that IGL-2 solution is suitable for protecting graft mitochondrial machinery and simplifying the complex logistics in clinical transplantation where traditional (static preservation) and innovative (HOPE) strategies may be combined. New mitochondrial markers are presented and discussed. The final goal is to take advantage of marginal livers to increase the pool of suitable organs and thereby shorten patient waiting lists at transplantation clinics.

Bardallo R, Calvo M, Folch-Puy E, Carbonell T, Palmeira C, Roselló Catafau J, Adam R. Polyethylene Glycol 35 as a Perfusate Additive for Mitochondrial and Glycocalyx Protection in HOPE Liver Preservation

Organ transplantation is a multifactorial process in which proper graft preservation is a mandatory step for the success of the transplantation. Hypothermic preservation of abdominal organs is mostly based on the use of several commercial solutions, including UW, Celsior, HTK and IGL-1. The presence of the oncotic agents HES (in UW) and PEG35 (in IGL-1) characterize both solution compositions, while HTK and Celsior do not contain any type of oncotic agent. Polyethylene glycols (PEGs) are non-immunogenic, non-toxic and water-soluble polymers, which present a combination of properties of particular interest in the clinical context of ischemia-reperfusion injury (IRI): they limit edema and nitric oxide induction and modulate immunogenicity. Besides static cold storage (SCS), there are other strategies to preserve the organ, such as the use of machine perfusion (MP) in dynamic preservation strategies, which increase graft function and survival as compared to the conventional static hypothermic preservation. Here we report some considerations about using PEG35 as a component of perfusates for MP strategies (such as hypothermic oxygenated perfusion, HOPE) and its benefits for liver graft preservation. Improved liver preservation is closely related to mitochondria integrity, making this organelle a good target to increase graft viability, especially in marginal organs (e.g., steatotic livers). The final goal is to increase the pool of suitable organs, and thereby shorten patient waiting lists, a crucial problem in liver transplantation.

Compared efficacy of preservation solutions in liver transplantation: a long-term graft outcome study from the European Liver Transplant Registry

Between 2003 and 2012, 42 869 first liver transplantations performed in Europe with the use of either University of Wisconsin solution (UW; N = 24 562), histidine-tryptophan-ketoglutarate(HTK; N = 8696), Celsior solution (CE; N = 7756) or Institute Georges Lopez preservation solution (IGL-1; N = 1855) preserved grafts. Alternative solutions to the UW were increasingly used during the last decade. Overall, 3-year graft survival was higher with UW, IGL-1 and CE (75%, 75% and 73%, respectively), compared to the HTK (69%) (p < 0.0001). The same trend was observed with a total ischemia time (TIT) >12 h or grafts used for patients with cancer (p < 0.0001). For partial grafts, 3-year graft survival was 89% for IGL-1, 67% for UW, 68% for CE and 64% for HTK (p = 0.009). Multivariate analysis identified HTK as an independent factor of graft loss, with recipient HIV (+), donor age ≥65 years, recipient HCV (+), main disease acute hepatic failure, use of a partial liver graft, recipient age ≥60 years, no identical ABO compatibility, recipient hepatitis B surface antigen (-), TIT ≥ 12 h, male recipient and main disease other than cirrhosis. HTK appears to be an independent risk factor of graft loss. Both UW and IGL-1, and CE to a lesser extent, provides similar results for full size grafts. For partial deceased donor liver grafts, IGL-1 tends to offer the best graft outcome.

Mechanistic analysis of nonoxygenated hypothermic machine perfusion's protection on warm ischemic kidney uncovers greater eNOS phosphorylation and vasodilation

Protection of endothelial cell function may explain the benefits of nonoxygenated hypothermic machine perfusion (MP) for marginal kidney preservation. However, this hypothesis remains to be tested with a preclinical model. We postulated that MP protects the nitric oxide (NO) signaling pathway, altered by static cold storage (CS), and improves renal circulation recovery compared to CS. The endothelium releases the vasodilator NO in response to flow via either increased endothelial NO synthase (eNOS) expression (KLF2-dependent) or activation of eNOS by phosphorylation (via Akt, PKA or AMPK). Using a porcine model of kidney transplantation, including 1 h of warm ischemia and preserved 24 h by CS or MP (n=5), we reported that MP did not alter the cortical levels of KLF2 and eNOS at the end of preservation, but significantly increased eNOS activating phosphorylation compared to CS. eNOS phosphorylation appeared AMPK-dependent and was concomitant to an increased NO-dependent vasodilation of renal arteries measured, ex situ, at the end of preservation. In vivo, laser Doppler showed that cortical microcirculation was improved at reperfusion in MP kidneys. In conclusion, we demonstrate for the first time, in a large-animal model, that MP protects the NO signaling pathway, confirming the value of MP for marginal kidney preservation.

Bortezomib enhances fatty liver preservation in Institut George Lopez-1 solution through adenosine monophosphate activated protein kinase and Akt/mTOR pathways

OBJECTIVES

The aim of this study is to investigate the protective mechanisms induced by bortezomib added to Institut George Lopez (IGL)-1 preservation solution to protect steatotic livers against cold ischaemia reperfusion injury and to examine whether these mechanisms occur through the activation of adenosine monophosphate activated protein kinase (AMPK), Akt/mTOR pathways.

METHODS

Steatotic livers from obese rats were preserved for 24 h (at 4 °C) in IGL-1 solution with or without bortezomib (100 nM) or pretreated with AMPK inhibitor adenine 9-α-D-arabinofuranoside and preserved in IGL-1 + bortezomib. Livers were then perfused for 2 h at 37 °C. Liver injury (alanine aminotransferase/aspartate aminotransferase) and function (bile production and vascular resistance) were measured. Also, Akt/mTOR, phosphorylated AMPK (pAMPK) and apoptosis were determined by Western blot analyses.

KEY FINDINGS

Bortezomib addition to IGL-1 solution significantly reduced steatotic liver injury, improved graft function and decreased liver apoptosis. These benefits were diminished by the pretreatment of obese rats with AMPK inhibitor Ara. Western blot analyses showed a significant increase in pAMPK after ischaemia and reperfusion. We also observed a significant phosphorylation of Akt in IGL-1 +bortezomib group that, in turn, induced the phosphorylation of mTOR and glycogen synthase kinase 3β.

CONCLUSIONS

Bortezomib, at low and non toxic concentration, is a promising additive to IGL-1 solution for steatotic liver preservation. Its protective effect is due to the activation of AMPK and Akt/mTOR pathways.