University of Groningen
Perioperative renal protective strategies in kidney transplantation
Nieuwenhuijs, Gertrude Johanna
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Perioperative renal protective
strategies in kidney transplantation
Gertrude Johanna Nieuwenhuijs-Moeke
Perioperative renal protective
strategies in kidney transplantation
Financial support for this thesis was provided by:
Graduate School of Medical Sciences Nierstichting Nederland
Nederlandse Transplantatie Vereniging Astellas Pharma BV
Chiesi Pharmaceuticals BV
Layout Bianca Pijl, www.pijlldesign.nl,
Groningen, the Netherlands
Cover Photography Marie Cécile Thijs
Printed by Ipskamp Printing
Enschede, the Netherlands
ISBN 978-94-028-1371-5 (print)
© Copyright 2019 G.J. Nieuwenhuijs-Moeke, Groningen, the Netherlands
All rights reserved. No part of this thesis may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without prior written permission of the author, or when
Perioperative renal protective
strategies in kidney transplantation
Proefschrift
ter verkrijging van de graad van doctor aan de Rijksuniversiteit Groningen
op gezag van de
rector magnificus prof. dr. E. Sterken en volgens besluit van het College voor Promoties
De openbare verdediging zal plaatsvinden op woensdag 27 maart 2019 om 16.15 uur
door
Gertrude Johanna Moeke
geboren op 17 januari 1976 te Hoogeveen
Promotores Prof. dr. M.M.R.F. Struys Prof. dr. H.G.D. Leuvenink Prof. dr. R.G. Ploeg Copromotor Dr. V.B. Nieuwenhuijs Beoordelingscommissie Prof. dr. A. R. Absalom Prof. dr. B. Beck-Schimmer Prof. dr. G. Molema
Voor Reinoud en Juliette
The individual has always had to struggle to keep from being overwhelmed by the tribe.
If you try it, you will be lonely often and sometimes frightened. But no price is too high to pay
for the privilege of owning yourself
Paranimfen Frouckje Hoekstra Martine Moeke
Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Table of contents
Introduction and rationale Mechanisms in injury and repair
Renoprotective capacities of non-erythropoietic EPO derivative, ARA290, following renal ischemia/reperfusion injury
ARA290, a non-erythropoietic EPO derivative, attenuates renal ischemia/reperfusion injury
Molecular mechanisms of renal ischemic conditioning strategies
Remote ischemic conditioning on recipients of deceased renal transplants does not improve early graft function. First results from the multicenter, randomised, controlled clinical trial CONTEXT
A propofol based anesthesia versus a sevoflurane based anesthesia in living donor kidney transplantation, results of the VAPOR-1 randomized controlled trial
Preemptively and non-preemptively transplanted patients show a comparable hypercoagulable state prior to kidney transplantation compared to living kidney donors
Intraoperative fluid restriction is associated with functional delayed graft function in living donor kidney transplantation, a clinical experience General discussion and future perspectives
Summary Nederlandse samenvatting List of publications List of abbreviations Biography Dankwoord
Addendum 1: protocol article CONTEXT Addendum 2: supplemental material VAPOR
9 23 53 69 85 125 141 167 191 207 245 251 263 269 279 283 295 307
Introduction and rationale
Introduction and rationale
A. Clinical dilemma
To date, 10% of the worldwide population suffers from chronic kidney disease (CKD). Prevalence of the disease will most likely grow over the next decade due to the increase in the elderly population and greater prevalence of diabetes and hypertension. In 2015 CKD was ranked 12th in the global list of causes of death.1 In 2010, 2.618 million patients had developed end stage renal disease (ESRD) and received renal replacement therapy (RRT), either dialysis or kidney transplantation. The population of patients needing RRT worldwide was estimated about 4.902 million (95% CI 4.438-5.431 million) in a conservative model and 9.701 million (95% CI 8.544-11.021 million) in a high estimate model, illustrating the magnitude of the disease burden of ESRD.2 For patients with ESRD, transplantation is still the optimal treatment. Long term survival with kidney transplantation is dramatically better than dialysis and transplantation provides a sustainably higher quality of life. Unfortunately, there is a worldwide shortage of suitable donor organs for (kidney) transplantation. The number of renal transplantations performed worldwide in 2016 was 69.500.3 Due to the persistent shortage of donor kidneys, many transplant centers have established large living donor programmes and transplant teams are also now accepting more older and higher risk organs retrieved from deceased donors. The use of these extended criteria donors (ECD) has affected outcomes after transplantation due to an often suboptimal quality of the donor organ. 4,5 As we will face more complex donors in the future with a reduced viability such as unstable donation after brain death (DBD) donors, donation after circulatory death (DCD) donors, and extended criteria donors (ECD), the challenge in transplantation is to be able to use these donor sources, however, without compromising successful immediate function and long-term graft survival after transplantation. It is therefore imperative that the condition of every graft-to-be ought to be optimised prior to or at time of transplantation, achieving the best possible post-transplant function and avoiding primary non function (PNF), delayed graft function (DGF), and rejection with chronic graft failure.
Perioperative medicine
Perioperative medicine involves the care of the patient that prepares for, undergoes, and recovers from a surgical procedure. It is patient-focused, multidisciplinary and the ultimate goal is to deliver the best possible health care from the moment the patient starts with his or her pre-operative assessment until he or she leaves the hospital in full recovery. Perioperative medicine ranges from preoperative risk assessment and optimization of high risk patients, to implementation of perioperative protocols (e.g. enhanced recovery after surgery, ERAS) and timely identification and effective treatment of postoperative deterioration or complications. Anesthesia societies all over the world are recognising a central role of the anesthesiologist in this rapidly evolving area of medicine. It extends the role of the anesthesiologist beyond the operating theatre to the wider hospital and the community. According to Grocott and Pearse perioperative medicine is the future of anesthesia.6 They postulate an interesting paradigm shift considering the response to surgery the primary “disease process” and the consequent organ dysfunction the condition to focus on.6 Traditionally, surgical care has focused on the operation and the disease being treated with this operation. Postoperative adverse events, however, are most likely the result of
the complex interplay between the underlying disease, the immune response to tissue injury of the surgical procedure and anesthesia as well as with the patient’s comorbidity and physiological reserve capacity.
Anesthesia per se has become very safe over the years. Injury directly ascribed to the conduct of anesthesia is rare and mortality rates solely attributable to anesthesia are reported between 0.03 and 1.71 per 10,000 anesthetic procedures.7 The substantial variation in patient outcome between institutions and countries, however, indicates that there may be avoidable injury during or after surgery in which anesthesia may play a contributing role. Most patients develop some degree of postoperative morbidity due to physiological changes and the endocrine and inflammatory responses to surgery and anesthesia. The long-term impact of these early postoperative consequences has been increasingly recognised. Khuri and colleagues performed a retrospective analysis of prospectively collected data in 105.951 patients undergoing eight different surgical procedures to identify determinants of long-term survival after major surgery.8 In this analysis the most important determinant was the occurrence of one of the 22 defined postoperative complications, ranging from superficial wound infection to acute kidney injury and cardiac arrest, within the 30-day postoperative period. The occurrence of complications reduced the median patient survival by 69% in the total patient study group, independent of patient’s preoperative risk.8 Even after full recovery, complications like pneumonia, deep wound infection and pulmonary embolism still negatively influences patient survival. The inflammatory response due to surgical induced trauma and anesthesia in its broadest definition may be one of underlying mechanisms of this phenomenon.9-13 Prolonged elevation of different cytokines IL-1b, IL-6, IL-8 and TNF-α), hormones (cortisol, aldosterone), acute phase proteins (C-reactive protein, CRP) and activation of the coagulation system are seen after surgery. Increasing evidence has been gained that intra-operative interventions like maintenance of normothermia, prevention of acidosis, optimization of the intraoperative fluid therapy, or choice of anesthetic technique reduce the incidence in postoperative complications.14-19 Hence, consequences or effects of our intraoperative choices and interventions will expand beyond the operating theatre and may attribute to postoperative adverse events or enhance recovery. To my opinion one of the roles of the anesthesiologist in perioperative medicine should be to gain better insight in intraoperative patient and organ protective strategies, allowing to reduce postoperative short and long-term complications.
Postoperative complications after kidney transplantation
During the procedure of organ donation and transplantation a number of potentially harmful processes will inevitably occur, affecting the viability of the kidney graft. Both donor and recipient are subjected to anesthesia and surgery, which will produce a sequence of systemic and local changes including a significant pro-inflammatory and pro-coagulatory response as described above.20 The donor organ is by definition exposed to a number of phases of injury from the moment the donor suffers from cerebral injury until the kidney is reconnected to the circulation in the recipient. These phases include a profound systemic and local inflammatory and pro-coagulatory response during donor management and retrieval, associated with hypoxia and ischemia of the kidney. In addition, prolonged warm ischemia in the DCD donor will affect the Chapter 1
viability of the donor kidney. These combined effects on the graft-to-be result in a cascade of renal damage that will reveal itself at the time of transplantation when the donor kidney is reperfused in the recipient and has been named ischemia-reperfusion injury (IRI).21 Typically, IRI will clinically manifest as immediate non function of the transplant with the need for dialysis treatment until the graft recovers from the insult and starts eventually to function. This ‘secondary’ recovery is called delayed graft function (DGF). In case the injury has been too extensive to repair the transplanted kidney will never recover and regain function which implies graft failure with permanent requirement of dialysis treatment for the patient. This is called primary non (and never) function (PNF). Currently, there are 22 definitions of DGF based on dialysis requirement, serum creatinine levels, urine output or a combination of these three.22 The most commonly used definition is at least one dialysis treatment during the first week after transplantation. The incidence of DGF in living donor kidney transplantation (LDKT) based upon this definition is low with incidences reported between 1-8% with an average of 5%.23,24 In brain dead donors the incidence increases to 15-25% and may rise up to 72% when kidneys are transplanted and retrieved from donation after circulatory death (DCD) donors.25 DGF is a clinically relevant problem. It is associated with an increase in morbidity, patient anxiety, prolonged hospitalisation and additional diagnostic procedures and costs. Furthermore, DGF is an important risk factor for acute rejection (AR) and the combination of DGF and AR reduces graft and patient survival.25,26 A meta-analysis of 34 studies between 1988 and 2007 showed a pooled incidence of AR of 49% in patients with DGF compared to 35% in patients without DGF with a relative risk (RR) 1.38 (95% CI 1.29–1.47).27 Most of these studies are performed in patients cohorts in the 90’s, but also in the present era when using modern immunosuppressive drugs, Wu and colleagues showed that the hazard ratio for AR is 1.66 (95% CI: 1.14, 2.42) in an unadjusted and 1.55 (95% CI: 1.03, 2.32) in a multivariable adjusted model in patients experiencing DGF compared to without DGF.28 Also, in the absence of AR, DGF has shown to be an independent risk factor for long term graft loss due to interstitial fibrosis and tubular atrophy (IFTA).29 Research regarding decreasing the incidence of DGF and/or rejection in kidney transplantation, predominantly focuses on donor treatment, organ preservation and post-operative recipient management, the vast majority involving immunosuppressive strategies. In this regard, the perioperative period as a window of opportunity to reduce DGF and improve outcome after kidney transplantation is undervalued. This is regrettable as most of the injury inflicted by ischemia and reperfusion will occur during the reperfusion phase in the recipient.30 The general aim of this thesis therefore is to evaluate renal protective strategies applied to the recipient during the transplantation procedure, and how can the anesthesiologist contribute to the improvement of short and long-term outcomes after kidney transplantation.
B. Rationale
Mechanisms in injury and repair
Since several aspects of of IRI and the coagulation system will be addressed and discussed in this thesis, an overview of relevant mechanisms in injury and repair is given in chapter 2.
Conditioning
Conditioning is a broad term generally used to describe strategies inducing biochemical changes that attenuate IRI. Dependant on the timing of application of the strategy it is referred to as pre- (before ischemia), per- (during ischemia) or post- (directly upon reperfusion) conditioning. It was first described in 1986 by Murray and collegues. They reported that subjecting the heart to four brief ischemic episodes followed by reperfusion, preceding a prolonged ischemic insult reduced myocardial infarct size by 75% in a canine model.31 This phenomenon is called ischemic preconditioning (IPC). Subsequently, it was found that ischemic conditioning (IC) upon reperfusion of the heart (ischemic post-conditioning, IPostC) or applied to a remote tissue or organ (remote ischemic conditioning, RIC) had a similar protective effect on the myocardium.32,33 Following the heart (R)IC was also described for various other organs including liver, brain, lungs and kidney.34-37 Furthermore several non-ischemic stimuli (like hyperthermia or transient pacing)38,39 and pharmacological substances (like volatile anesthetics, opioids, erythropoietin, nicorandil) were also found to be able to confer cellular tolerance to a major ischemic period by underlying mechanisms similar to those mediating IC.40-45 In chapter 3-7 three different conditioning strategies are tested.
1. Pharmacological conditioning with the use of erythropoietin derivate ARA290
Erythropoietin (EPO) is produced and secreted by the kidney in response to anemia. It stimulates erythropoiesis in the bone marrow. Next to this, EPO possesses anti-apoptotic, anti-inflammatory and cytoprotective effects. It is released in different cell lines and organs upon innate immune cell activation including the kidney and acts as the systems’ own protector against tissue stress or injury.46-48 In renal I/R models it has been shown that the administration of EPO before as well as after reperfusion is able to attenuate renal IRI.49,50 Erythropoiesis is mediated by binding of EPO to the homodimeric complex of two EPO receptors (EPOR2) on erythroid progenitor cells.51 Cytoprotection is presumed to be mediated by an alternative receptor consisting of a heterodimeric binding of an EPOR and a β common receptor (βcR, also known as CD131).52 Collino and colleagues called this receptor complex the Inate Repair Receptor (IRR) pointing out its protective role in inflammation in tissue injury to reduce damage and initiation of healing and repair.53 The affinity of EPO for the EPOR-βcR complex is approximately 80 times lower than its affinity for the EPOR2.54 This implicates that high plasma concentrations of EPO are required when exogenous EPO is used to induce cytoprotection. This is a major drawback in the clinical setting because of the simulative effect of EPO on various progenitor pools (including megakaryocyte progenitors) in the bone marrow and the risk of cardiovascular and thromboembolic complications. High dose of EPO raises not only the hematocrit but also enhances platelet count and activity and endothelial activation.55 To avoid these adverse events various cytoprotective Chapter 1
EPO derivatives have been developed that only activate the EPOR-βcR complex and do not stimulate hematopiosis.56 ARA290 is an 11 amino acid peptide that selectively binds to the EPOR-βcR complex. It has an ultra-short half-life of several minutes. ARA290 has been shown to have no erythropoietic properties and to be renoprotective in a rodent model of renal I/R.56,57 In chapter 3 and 4 the hypothesis that the administration ARA290 post reperfusion is renoprotective in a renal I/R model in rats (chapter 3) and pigs (chapter 4) is tested. Additionally, we focussed on optimum timing of administration and investigated the anti-inflammatory properties of ARA290.
2. (Remote) ischemic conditioning
Chapter 5 provides an overview of the molecular mechanisms underlying both ischemic and remote ischemic conditioning of the kidney. This chapter discusses the results of the animal experiments and clinical trials performed in this research area, reporting renal endpoints. Additionally on-going clinical trials exploring (R)IC in renal context are reviewed. In chapter 6 the concept of RIC in renal transplantation is brought from bench to bedside in the CONTEXT study. In this study the RIC procedure is initiated after start of surgery and consists of 4 cycles of 5 min inflation of a tourniquet around the thigh followed by 5 minutes of reperfusion, before reperfusion of the kidney. Primary endpoint is the estimated time to a 50% decrease in plasma creatinin. The complete study protocol of the CONTEXT study can be found as addendum 1. 3. Anesthetic conditioning with volatile anesthetics agents
Experimental data have demonstrated that some of the generally used anesthetics and analgesic agents are able to modulate IRI by underlying mechanisms partially similar to those mediating IC. This phenomenon is called anesthetic conditioning (AC) and is in particular attributed to volatile anesthetic (VA) agents, like sevoflurane or isoflurane, and to a much lesser extend to the intravenous anesthetic agent propofol. Therefore we designed the Volatile Anesthetic Protection Of Renal transplant (VAPOR) trial. This two-step study looks at the effect of two commonly used anesthetic regimens (propofol-remifentanil anesthesia vs sevoflurane-remifentanil anesthesia) on renal outcome in kidney transplantation. In chapter 7 the results of the VAPOR-1 trial, a single center proof of concept study in LDKT are reported. We hypothesized that a sevoflurane based anesthesia is able to induce renal AC and thereby reduces post-transplant renal injury reflected by lower levels of kidney injury biomarkers compared to propofol based anesthesia.
Preoperative coagulatory state of renal transplant recipients
A rare form of delayed graft function is renal artery or vein thrombosis. Although the incidence is low it is major cause of (up to 45%) of early graft loss.58-60 International guidelines to prevent renal graft thrombosis in the intra-and early post-operative period are lacking due to concerns over increased risk of bleeding complications and lack of agreement of which patients have to be considered high risk. Therefore various intra- and postoperative antithrombotic strategies are used among centers, ranging from no anti-coagulation therapy to unfractionated heparin (UFH) for several days post transplantation in high risk patients. In the University Medical Center of Groningen preemptively transplanted patients are given 5000 IU of UFH intraoperatively before clamping of the vessels and non-preemptively transplanted, dialysis dependent,
patients are not. Historically, dialysis dependent patients (especially hemodialysis, HD) were considered hypocoagulable due to the residual effect of heparin used during dialysis and the continuous activation of platelets through contact with the dialysis membrane.61,62 Therefore, in various risk stratification algorithms patients on HD are considered low risk and “no thrombotic prophylaxis” in the perioperative transplantation period is advised.63 Recent insights, however, suggest otherwise.64 In chapter 8 the coagulatory state of preemptively and dialysis dependant transplanted patients before and after kidney transplantation is evaluated. Results are compared with living kidney donors undergoing laparoscopic donor nephrectomy.
Intraoperative fluid management
Several studies suggest that a supra-normal fluid state during the transplantation procedure is associated with a reduced risk of DGF.65-71 Unfortunately, many of these studies, are retrospective and often comprise a variety of donor types with variable incidences of DGF hampering an adequate analysis. Although an “adequate” intravascular volume or slight overhydration is suggested and avoidance of hypovolemia is advised,67,72-74 it is unclear how this adequate fluid state should be defined or measured. So to date there is no consensus on fluid management during kidney transplantation, neither on type of fluid nor the volume or the recommended way to monitor fluid administration. Recently goal directed fluid therapy (GDFT) has been shown to improve patient outcome after major (abdominal) surgery.75-77 GDFT uses advanced hemodynamic monitoring to evaluate and optimize the individual fluid state, cardiac output and oxygen supply to the tissues.78 Fluid administration and vasopressic or inotropic support in these protocols is guided by fluid responsiveness and individual goals based upon the Frank Starling curve. Fluid responsiveness indicates a state in which an increase in vascular volume increase the stroke volume (SV) and cardiac output (CO). Frequently used dynamic parameters to guide GDFT are stroke volume variation (SVV), derived from a pulse contour analysis, or pulse pressure variation (PPV), derived from the arterial waveform. A SVV or PPV > 12 - 13% has been proven to be a good predictor of fluid responsiveness.79-83 Since kidney transplant patients present in a variety of fluid states at the time of surgery this personalized intra operative fluid approach seemed very attractive in this group of patients and was implemented in our kidney transplant programm. In chapter 9 we will evaluate the impact of the implementation of a GDFT protocol in our LDKT population.
The results of this thesis and future perspectives will be discussed in chapter 10. Chapter 1
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22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 Chapter 1
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Collino M, Thiemermann C, Cerami A, Brines M. Flipping the molecular switch for innate protection and repair of tissues: Long-lasting effects of a non-erythropoietic small peptide engineered from erythropoietin. Pharmacol Ther. 2015;151:32-40
Brines M, Cerami A. Erythropoietin-mediated tissue protection: reducing collateral damage from the primary injury response. J Intern Med. 2008; 264(5):405-32
Stohlawetz PJ, Dzirlo L, Hergovich N, Lackner E, Mensik C, Eichler HG et al. Effects of erythropoietin on platelet reactivity and thrombopoiesis in humans. Blood. 2000; 95:2983-9
Brines M, Patel NS, Villa P, Brines C, Mennini T, De Paola M et al. Nonerythropoietic, tissue-protective peptides derived from the tertiary structure of erythropoietin. Proc Natl Acad Sci U S A. 2008; 105:10925-30 Patel NS, Kerr-Peterson HL, Brines M, Collino M, Rogazzo M, Fantozzi R et al. The delayed administration of pHBSP, a novel non-erythropoietic analogue of erythropoietin, attenuates acute kidney injury. Mol Med. 2012; 18:719-27
Keller AK, Jorgensen TM, Jespersen B. Identification of risk factors for vascular thrombosis may reduce early renal graft loss: a review of recent literature. J Transplant. 2012; 793461
Hamed MO, Chen Y, Pasea L, Watson CJ, Torpey N, Bradley JA, et al. Early graft loss after kidney transplantation: risk factors and consequences. Am J Transplant. 2015; 15(6):1632-43
Bakir N, Sluiter WJ, Ploeg RJ, van Son WJ, Tegzess AM. Primary renal graft thrombosis. Nephrol Dial Transplant.1996; 11(1):140-7
Strolli V, Ballone E, Di Stante S, Amoroso L, Bonomini M. Cell activation and cellular-cellular interactions during hemodialysis: effect of dialyzer membrane. Int J Artif Organs 2002; 25:529-37
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Eknoyan G, Wacksman SJ, Glueck HI, Will JJ. Platelet function in renal failure. N Engl J Med. 1969; 280(13):677-81
Ojo AO, Hanson JA, Wolfe RA, Agodoa LY, Leavey SF, Leichtman A et al. Dialysis modality and the risk of allograft thrombosis in adult renal transplant recipients. Kidney Int.1999; 55(5):1952-601
Lutz J, Menke J, Sollinger D, Schinzel H, Thürmel K. Haemostasis in chronic kidney disease. Nephrol Dial Transplant. 2014; 29(1):29-40
Siedlecki A, Irish W, Brennan DC. Delayed graft function in the kidney transplant. Am J Transplant. 2011; 11 :2279-96
Snoeijs MG, Winkens B, Heemskerk MB et al. Kidney transplantation from donors after cardiac death: a 25-year experience. Transplantation. 2010; 90:1106-12
Perico N, Cattaneo D, Sayegh MH, Remuzzi G. Delayed graft function in kidney transplantation. Lancet. 2004; 364:1814-27
Othman MM1, Ismael AZ, Hammouda GE. The impact of timing of maximal crystalloid hydration on early graft function during kidney transplantation. Anesth Analg. 2010; 110:1440-6
Bacchi G, Buscaroli A, Fusari M, Neri L, Cappuccilli ML, Carretta E et al. The influence of intraoperative central venous pressure on delayed graft function in renal transplantation: a single-center experience. Transplant Proc. 2010; 42:3387-91
Snoeijs MG, Wiermans B, Christiaans MH, van Hooff JP, Timmerman BE, Schurink GW et al. Recipient hemodynamics during non-heart-beating donor kidney transplantation are major predictors of primary nonfunction. Am J Transplant. 2007; 7:1158-66
Aulakh NK, Garg K, Bose A, Aulakh BS, Chahal HS, Aulakh GS. Influence of hemodynamics and intra- operative hydration on biochemical outcome of renal transplant recipients. J Anaesthesiol Clin Pharmacol. 2015; 31:174-9
Siedlecki A, Irish W, Brennan DC. Delayed graft function in the kidney transplant. Am J Transplant. 2011; 11:2279-96
Carlier M, Squifflet JP, Pirson Y, Gribomont B, Alexandre GP. Maximal hydration during anesthesia increases pulmonary arterial pressures and improves early function of human renal transplants. Transplantation. 1982;34:201e4
Carlier M, Squifflet JP, Pirson Y, Decocq L, Gribomont B, Alexandre GP. Confirmation of the crucial role of the recipient’s maximal hydration on early diuresis of the human cadaver renal allograft. Transplantation. 1983; 36:455e6
Benes J, Giglio M, Brienza N, Michard F. The effects of goal-directed fluid therapy based on dynamic parameters on post-surgical outcome: a meta-analysis of randomized controlled trials. Crit Care. 2014; 18:584
Ripollés-Melchor J, Espinosa Á, Martínez-Hurtado E, Abad-Gurumeta A, Casans-Francés R, Fernández- Pérez C et al. Perioperative goal-directed hemodynamic therapy in noncardiac surgery: a systematic review and meta-analysis. J Clin Anesth. 2016; 28:105-15
Sun Y, Chai F, Pan C, Romeiser JL, Gan TJ. Effect of perioperative goal-directed hemodynamic therapy on postoperative recovery following major abdominal surgery-a systematic review and meta-analysis of randomized controlled trials. Crit Care. 2017; 21:141
Marx G, Cope T, McCrossan L, Swaraj S, Cowan C, Mostafa SM et al. Assessing fluid responsiveness by stroke volume variation in mechanically ventilated patients with severe sepsis. Eur J Anaesthesiol. 2004; 21:132-8
Cannesson M, Musard H, Desebbe O, Boucau C, Simon R, Hénaine R et al The ability of stroke volume variations obtained with Vigileo/FloTrac system to monitor fluid responsiveness in mechanically
62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 Chapter 1
Michard F, Boussat S, Chemla D, Anguel N, Mercat A, Lecarpentier Y et al. Relation between respiratory changes in arterial pulse pressure and fluid responsiveness in septic patients with acute circulatory failure. Am J Respir Crit Care Med. 2000; 162:134-8
Feissel M, Michard F, Mangin I, Ruyer O, Faller JP, Teboul JL. Respiratory changes in aortic blood velocity as an indicator of fluid responsiveness in ventilated patients with septic shock. Chest. 2001; 119: 867-73 Marik PE, Cavallazzi R, Vasu T, Hirani A. Dynamic changes in arterial waveform derived variables and fluid responsiveness in mechanically ventilated patients. A systematic review of the literature. Crit Care Med. 2009; 37:2642–7
Marik PE, Monnet X, Teboul JL. Hemodynamic parameters to guide fluid therapy. Ann Crit Care. 2011; 1:1
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Mechanisms in injury and repair
I/R
DAMPscell death programs
apoptosis (regulated) necrosis autophagy endothelial dysfunction vascular permeabilitity vasoconstriction, no reflow transmigration leukocytes activation innate en adaptive immune system
transcriptional reprogramming
HIF Relevant mechanisms in injury and repair
1. Ischemia and reperfusion injury
One of the most important mechanisms underlying DGF is ischemia and reperfusion injury (IRI). IRI is a consequence of ischemia and reperfusion (I/R) and inevitable in (kidney) transplantation. It consists of a complex pathophysiology involving activation of cell death programs (apoptosis, necrosis, necroptosis), endothelial dysfunction, transcriptional reprogramming and activation of the innate and adaptive immune system (fig. 1).1 Numerous pathways and signalling cascades are implicated.
Figure 1. Schematic overview of the pathophysiological consequences of ischemia and reperfusion
Ischemia
Due to a decrease in oxygen supply, cells will switch from an aerobic to an anaerobic metabolism which results in a decrease in ATP production and intracellular acidosis due to the formation of lactate. This causes destabilisation of lysosomal membranes with leakage of lysosomal enzymes, breakdown of the cytoskeleton and inhibition of membrane bound Na+/K+-ATPase activity. This last process gives rise to an intracellular accumulation of Na+-ions and water with as a consequence cellular edema. Due to a declined Ca2+ excretion there is also an intracellular Ca2+ accumulation which causes activation of Ca2+-dependant proteases like calpains. These calpains stay inactive during the ischemic period due to the acidosis but may damage the cell after normalisation of the pH during reperfusion. In the mitochondria the Ca2+ overload is responsible for the generation of reactive oxygen species (ROS). This will lead to opening of the mitochondrial permeability transition pores (mPTP) after reperfusion. During the ischemic period only small amounts of ROS are produced compared to the entire I/R process because of the redox reduction of cytochromes, nitric oxide synthases, xanthine oxidase and NADPH oxidase activation.
ischemia ATP depletion inhibition Na+/K+ pump intracellular accumulation Na+, Ca2+, edema enzymeactivation proteases ROS acidosis lysosomal instability release lysosomal enzymes injury cytoskeleton, cellular membrane, mitochondria , DNA necrosis, apoptosis reperfusion
reoxygenation, ATP pH normalisation ROS Ca2+ load
opening mPTP activation proteases
injury cytoskeleton, cellular membrane, mitochondria, DNA necrosis, apoptosis
Reperfusion
During reperfusion oxygen levels increase and the pH normalises. pH normalisation is dangerous for the previously ischemic cells. The intracellular Ca2+ level further increases which activates the calpains causing injury to the cell structure and cell death. Due to normoxemia large quanteties of ROS are produced together with a reduction in the antioxidant capacity. These ROS contributes to injury of the cell membranes, the cytoskeleton and DNA. Additionally the combination of ROS and increase in mitochondrial Ca2+ load causes opening of the mPTP which leads to cell death trough apoptosis and necrosis. Most of the injury will occur during this reperfusion phase.1 Figure 2 provides a schematic overview of the intracellular consequences of I/R.
Figure 2. Cellular consequences of I/R
ROS: reactive oxygen species; mPTP: mitochondrial permeability transition pore
2. Pathophysiology of IRI
I/R gives rise to several pathophysiological processes that may damage the kidney. 2A. Cell death: apoptosis, necrosis and autophagy
I/R leads to the activation of cell death programs. Of these programs necrosis is the most uncontrolled form. It is due to swelling of the cell and subsequent rupture of the cellular membrane.2 This will lead to an uncontrolled release of cellular fragments into the extracellular space. These fragments act as damage/danger associated molecular patterns (DAMPs) and are able to activate the innate and adaptive immune system entailing infiltration of inflammatory cells into the tissue and release of different cytokines.
This is in contrast to the highly regulated and controlled process of apoptosis in which activation of the caspase signalling cascade results in a self-limiting programmed cell death. The caspases, a family of proteases, are essential for the process of apoptosis. There are two types of caspases: Chapter 2
initiator caspases (caspase 2, 8, 9, 10) and effector caspases (caspase 3, 6, 7).3,4 The initiator caspases are activated by binding to a specific activator protein complex (DISC, apoptosome).5 These complexes activate the effector caspases through proteolytic cleavage upon which the effector caspases proteolytically degenarate various intracellular proteins.
Apoptosis gives rise to apoptotic bodies, containing these intracellular protein fragments, via the process of membrane blebbing. The apoptotic bodies will undergo phagocytosis before they can spill their content into the extracellular space and therefor will generate a less immune stimulating impulse compared to necrosis. Apoptosis can be initiated through an intrinsic pathway (mitochondrial dependent pathway) in which the initiating signal comes from within the cell (e.g. damaged DNA, hypoxia, metabolic stress) or an extrinsic pathway (cell death receptor pathway) due to signals from out of the cell (TNF-α, Fas-ligand).5 A protein family which plays an important role in the regulation of apoptosis is the BcL-2 family.6 Members of this family can act as protectors (BcL-2, BcL-xL) which inhibit apoptosis, sensors (BH3 only proteins, Bad, Bim, Bid) which inhibit the protectors, or effectors (Bax, Bad) which initiate apoptosis by enhancing the permeability of the mitochondrial membrane.7
The intrinsic pathway is mediated by intracellular signals of cell stress leading to an increase in the BH3 only proteins resulting in an inhibition of the protectors and activation of the effectors. The effectors Bax and Bad increase the permeability of the mitochondrial membrane (MOMP: mitochondrial outer membrane permeabilisation) resulting in leakage of apoptotic proteins. One of these mitochondrial proteins, known as SMAC (second mitochondria-derived activator of caspases), binds to proteins that inhibit apoptosis (IAPs, by suppression of the caspase proteins) causing an inactivation of the IAPs.8-10 Another protein released from the mitochondria, due to formation of a mitochondrial apoptosis-induced channel in the outer mitochondrial membrane, is cytochrome c.11 Upon release it binds with Apoptotic protease activating factor-1 (Apaf-1) and ATP. Next this complex binds to pro-caspase 9 creating a protein complex known as the apoptosome. The apoptosome cleaves pro-caspase 9 to its active form of caspase 9, which in turn is able to activate the effector caspase 3.
The extrinsic pathway is mediated through receptors of the TNF receptor (TNFR) family either via the TNF path or the Fas (first apoptosis signal) path.12 In the TNF path binding of TNF-α (produced by macrophages, NK-cells or CD4+ T cells) to a trimeric complex of TNFR1 molecules induces activation of the intracellular death domain and the formation of the receptor-bound complex 1 made up of TRADD (TNF receptor-associated death domain), RIPK1 (Receptor-interacting protein kinase 1), two ubiquitin ligases: TNFR-associated factor (TRAF)-2 and cellular inhibitors of apoptosis (clAP)1/2 and the linear ubiquitin assembly complex LUBAC. This complex 1 can lead to a pro-survival pathway or to apoptosis. In case of apoptosis the TRADD dependant complex IIa (consisting of TRADD, Fas-associated death domain protein (FADD) and caspase 8) or the RISK-1 dependant complex IIb also known as the ripoptosome (consisting of FADD, RIPK1, RIPK3 and caspase 8) is formed.13,14 In the Fas path, presence of the Fas ligand (FasL, expressed on cytotoxic T lymphocytes) causes three Fas receptors (CD95) to trimirize. This clustering and binding to the FasL initiates the binding of FADD. Three procaspase 8 or 10 molecules can then interact with the complex by their own death effector domains. The complex formed is called the death-inducing signalling complex (DISC). The DISC cleaves and activates complex 8 and 10.15 Activation of the initiator caspase 8 by both paths directly activates other members of the caspase signalling
SMAC MOMP mitochondrion Activated BAX-BAD Cytochrome c BH3-only proteins Bcl-2 Bcl-XL IAP Intrinsic lethal stimuli, DNA damage, hypoxia
Caspase 9 Caspase 3 Caspase 7 Apoptosis APAF-1 Caspase 3 Caspase 7 Caspase 8 Caspase 10 DISC BID BID Extrinsic pathway Intrinsic pathway TNF- FAS-L Apoptosome
cascade such as the eff ector caspase 3 but also can lead to an increase in BH3-only proteins (Bim, Bid) and trigger the intrinsic pathway.16 Figure 3 provides a schematic overview of the diff erent apoptotic pathways.
Figure 3. Extrinsic and intrinsic apoptotic pathway.
TNF-α: tumor necrosis factor-α; FAS-L: FAS ligand; FADD: Fas associated death domain; TRADD: TNF receptor- associated death domain; DISC: death-inducing signaling complex; MOMP: mitochondrial outer membrane permeabilisation; SMAC: second mitochondria-derived activator of caspases; IAP: inhibiting apoptosis proteins; APAF-1: Apoptotic protease activating factor
Adapted from Larry Li, Biologydictionary.net Editors. “Organ” Biologydictionary.net. 2014
Recently new pathways of a more regulated form of necrosis have been described. This process shows features of apoptosis as well as necrosis and is called necroptosis.14 One of the best-known pathways of necroptosis is via TNFR-1. In the absence of active caspase 8, phosphorylation of RIPK1 and RIPK3 in complex IIb leads to formation of a complex called the necrosome. The necrosome recruits Mixed Kinase Domain Like protein (MLKL) , which is than phosphorylated by RIPK3.14 MLKL activates the necrosis phenotype by entering the bilipid membranes of organelles and the cellulair membrane. This causes formation of pores in these membranes and leads to release of cellular contents, functioning as DAMPs, into the extracellular space.17 As in necrosis the DAMPs are able to activate both the innate and adaptive immune system promoting proinfl ammatory responses that activate rejection pathways.18,19 A recent study in a kidney transplant mouse model showed that RIPK3-defi cient kidneys had better function and longer rejection-free survival.20 Therefore RIPK3-inhibiting drugs might be of interest in the reduction of IRI in organ transplantation. Next Chapter 2
to TNRF-1, other death receptors and toll like receptors (TLR) have shown to be able to induce necroptosis.14
Finally, cells can preserve their metabolic function and escape cellular death. This due to autophagy of damaged cell parts. There are several pathways of autophagy of which macro-autophagy is the best studied. It involves formation of autophagosomes containing damaged cell parts or unused proteins. These double membrane autophagosomes travel through the cytoplasm to fuse with lysosomes (autolysosome) leading to the degradation of the damaged cell parts. This process is continuously active at low basal levels, preserving cellular homeostasis, but stimulated upon stress through various signals like nutrient deprivation, ROS formation, hypoxia, free amino acids
etc.21-23 The first step in autophagy, the initiation, is regulated by two kinases: mammalian target
of rapamycin complex 1 (mTOR, mTORC1), a member of the phosphatidylinositol 3-kinase-related kinase family, and AMP-activated kinsase (AMPK).21,24,25 Together they regulate the activity of the ULK1/2 complex consisting of Unc-51 like autophagy activating kinase (ULK1/2), the FAK family kinase interacting protein of 200 kDa (FIP200) and the autophagy related proteins ATG13 and ATG10.26,27 Activation of mTOR leads to the inhibition of autophagy (for instance through the PI3K/ AKT or the MAPK/Erk 1/2 signaling pathway) whereas activation of AMPK activates autophagy.28 AMPK, activated upon intracellular AMP increase, is able to activate autophagy by inhibition of the mTORC1 through dissociation of mTORC1 from ULK1/2 allowing ULK1/2 to be activated.29,30 AMPK, is also able to initiate autophagy in a direct way by phosphorylation of ULK1/2 forming the ULK1/2-complex.29 Another complex involved in the initiation of autophagy is the autophagy inducible beclin-1 complex or class III PI3K complex which consists of Vps34 (class III PI3K), beclin-1 (a BH3 only domain protein member of the Bcl-2 family), vps15 and ATG14L. This complex is activated by the ULK-1 complex and inhibited by Bcl-2 and Bcl-XL. The ULK1/2 and class III PI3K complexes join to form the phagopore and eventually the autophagosme.31-33 This process is mediated by the Atg5-Atg12-Atg16 complex and the formation of phosphatidylethanolamine-conjungated Light Chain (LC) 3 (LC3-II) facilitating elongation of the bilipid membrane to form a closed autophagosme.31,32,34-36 This autophagosome fuses with a lysosome in which LC3-II located on the inner membrane is degraded together with the content of the autophagosome. The LC3-II molecules adhered to the outer membrane are split off by Atg4 and recycled.33 Finally the content of the autolysosome is degenerated and the components are released to be reused to synthesise new proteins or to function as an energy source for the cell.37 Figure 4 illustrates the process of macro-autophagy.
During micro-autophagy, cytoplasmatic contents are directly engulfed into the lysosome without formation of a autophagosome.38 A very selective form of autophagy is the chaperone mediated autophagy (CMA) reserved for proteins with the recognition site for the hsc70 (heat shock cognate 70 of the Hsp70 family) containing complex.39,40 Binding of these specific proteins to this chaperone complex leads to formation of the CMA-substrate/chaperone complex which binds to the lysosome-associated membrane type 2A (LAMP2A) on the lysosomal mebrane. Upon recognition, the substrate protein unfolds and translocates across the membrane with the assistance of the hsc70 chaperone.41,42
autophagosome autolysosome phagophore LC3-II LC3-II LC3-II LC3-II ATG3 ATG4 Lysosome ATG16 ATG12 ATG5
mTORc1 AKT PDK1 PI3K-I
ULK ATG10 FIP200 ATG13 AMPK ATG14 Beclin-1 VPS34 VPS15 ULK complex PI3K-III complex ATG9 Bcl-2 Bcl-XL Nutrient depletion stress Nutrient abundance
Growth factor receptor
Figure 4. Pathway of macro-autophagy
AMPK: AMP-activated kinsase; mTORc1: mammalian target of rapamycin complex 1; AKT: Protein kinase B; PDK1: pyruvate dehydrogenase kinase 1; PI3K-1: phosphatidylinositol 3-kinase; ATG: autophagy related proteins; ULK: Unc-51 like autophagy activating kinase; FIP200: FAK family kinase interacting protein of 200 kDa; VPS: phosphatidylinositol 3-kinase; LC3-II: phosphatidylethanolamine-conjungated Light Chain (LC) 3
Adapted from: InVivogen (San Diego, California, US)
In renal IRI, autophagy is mostly upregulated, but both protective and harmful effects are observed, proposing a dual role for autophagy in renal IRI.43,44 Autophagy can be considered a protective mechanism in (oxidative) stress injured cells trough restoring cellular homeostasis. Kidneys from older donors are at increased risk of DGF. The age dependent decline in autophagy activity may be one of the underlying mechanisms of this phenomenon.45 Extensive oxidative stress (amount or duration), however, may have detrimental effects which eventually could trigger the switch to aggravation of the injury through autophagy dependant cell death. Excessive or prolonged ROS exposure may lead to the oxidative modification of macromolecules making them only partially degradable by the autolysosome. This indestructible product, known as lipofuscin, impairs functioning of the lysosomes and exacerbates injury.46 Furthermore an energy dependent process of autophagy could deprive the cell of needful energy. In this light excessive autophagy seen upon a prolonged duration of cold ischemia time and in DCD donors seems to be one of the underlying mechanisms behind augmentation of reperfusion injury seen in these circumstances, increasing the risk of DGF.43,47
The different cell death programs described above are induced in response to common stimuli. Several proteins in the autophagy and apoptosis pathway are shared resulting in an intimate crosstalk between apoptosis and autophagy. Regulation of these proteins determines cellular Chapter 2
fate to cell survival or cell death. Caspase mediated degradation of several autophagy regulation proteins limits autophagosome formation and therefore autophagy.48-50 Apoptosis inhibitors Bcl-2 and Bcl-XL also inhibit autophagy by binding to Beclin-1 limiting its availability to form the classIII PI3K complex.51,52 Inhibition of cisplatin induced autophagy enhanced caspase 3 activation and apoptosis in renal proximal tubular cells.53,54 On the other hand overexpression of Atg5 and beclin-1 prevented cisplatinum induced caspase activation and apoptosis.55 Addiotionally there is evidence that autophagy induction regulates necroptosis. Inhibition of autophagy have shown to prevent necroptosis and vice versa inhibition of necroptosis is able to supress autophagy.56,57 2B. Endothelial dysfunction
At a vascular level, I/R leads to swelling of the endothelial cells, loss of the glycocalyx and degradation of the cytoskeleton. As a consequence intercellular contact of endothelial cells is lost, increasing vascular permeability and fluid loss to the interstitial space.58 Furthermore the endothelium will produce vasoactive substances like platelet derived growth factor (PDGF) and Endothelin-1 (ET-1), causing vasoconstriction.59 This vasoconstriction can be enhanced by a reduced NO production during the reperfusion due to decreased endothelial nitric oxide synthase (eNOS) expression and increased sensitivity of the arterioles for vasoactive substances like angiotensin II, thromboxane A2 and prostaglandin H2.60-62 Eventually this can lead to the so called no reflow phenomenon characterized by the absence of adequate perfusion on microcirculatory level despite reperfusion.
An important feature of IRI is the chemotaxis of leukocytes, endothelial adhesion and transmigration of these cells into the interstitial compartment.63 This process is initiated by increased expression of P-selectin on the endothelial cells and interaction of P-selectin with P-selectin glycoprotein 1 (PSGL-) expressed on the leukocytes. This interaction results in rolling of the leukocytes on the endothelium. Subsequently firm adherence of the leucocytes to the endothelium is achieved by the interaction of the β2-integrins lymphocyte function-associated antigen 1(LFA-1) and macrophage-1 antigen (MAC-1 or complement receptor 3, CR3) on the leukocyte and the intracellular adhesion molecule 1 (ICAM-1) on the endothelial cells. Platelet endothelial cell adhesion molecule 1 (PECAM-1) thereafter facilitates transmigration into the interstitial space. Once activated these leukocytes will release several toxic substances like ROS, proteases, elastases and different cytokines in the interstitial compartment which will result in further injury like increased vascular permeability, edema, thrombosis and parenchymal cell death.64 Figure 5 depicts the interaction of leukocytes and the endothelium upon IRI.
2C. Innate and adaptive immune response
IRI is accompanied by sterile inflammation in which the innate as well as the adaptive immune system are involved.
Innate immune response
The innate, or in-born or non-specific, immune system is evolutionary the oldest part of the immune system. It acts on infection or injury with a fast, short-lasting and aspecific response in which different cells and systems are involved. In the innate immune response, the toll-like
intravascular interstitial space endothelial cell PECAM-1 ICAM-1 p-selectin
rolling binding transmigration
ROS proteases elastases LFA-1 psgl-1 leukocyte
Figure 5. Interaction of leukocytes and endothelial cells in the process of transmigration of leukocytes Psgl-1: P-selectin glycoprotein 1; LFA-1: lymphocyte function-assisted antigen 1; ICAM-1: intracellular adhesion molecule 1; PECAM-1: platelet endothelial cell adhesion molecule 1; ROS: reactive oxygen species
Adapted from: Salvadori M, Rosso G, Bertoni E. Update on ischemia-reperfusion injury in kidney transplantation: Pathogenesis and treatment. World J Transplant. 2015; 5(2):52-67
receptors (TLRs) play an important role.65 TLRs are transmembrane proteins and are members of the interleukin-1 receptor (IL-IR) superfamily. They function as pattern recognition receptors (PRR) and are present on the cellular membrane and in the cytosol of cells like leukocytes, endothelial cells and tubular cells.66 DAMPs released upon injury are able to activate these TLR’s. The DAMPs vary greatly depending on type of injury and tissue involved. High-mobility group box-1 (HMGB-1), an intracellular protein involved in the organisation of DNA and the regulation of gene transcription, is one of the DAMPs linked to the pathogenesis of IRI.67-69 From the nucleus HMGB-1 can be released into the cytosol or extracellular space by passive leakage from injured cells or through active secretion by immune cells.70,71 In general, activation of the TLRs lead to the recruitment of various adapter molecules (TRAF6, MyD88, TIRAP, TRAM, TRIP). These adapter molecules activate different kinases (IRAK-1, IRAK-4, TBK, IKK) which will lead to activation of transcription factors (NF-κB, MAP3, IFR) and eventually results in an inflammatory response.1 In renal IRI, TLR4 plays an important role. Bergler and colleagues showed that TLR4 is highly upregulated after renal IRI, and that high TLR4 expression is strongly correlated with graft function in an allogenic renal transplant model in rats.72 Furthermore, TLR4 deficient mice are protected against renal IRI and kidneys from donors with a TLR4-loss of function allele show less pro inflammatory cytokines in the kidney after transplantation and a higher percentage of immediate graft function.73,74 Proposed endogenous ligands for TLR4 in renal IRI include HMGB-1 extracellular matrix (ECM) components like biglycan, heparin sulphate and soluble hyaluronan, and heat shock proteins (Hsps).75-81 Upon ligand binding, activation of TLR4 leads to downstream signalling via the MyD88 dependent and MyD88 independent pathway. The MyD88 dependent pathway in which MyD88 and TIRAP or MyD88 adapter-like (Mal) recruits and activates members of the IL-1 receptors associated kinases (IRAK) Chapter 2
and subsequently activation of TAK1. Activation of TAK1 than leads to the activation of inhibitor of nuclear factor-κB kinase (IKK) which results in the release of NF-κB from its inhibitor, promoting translocation to the nucleus. The MyD88 independent pathway is mediated by the adapter molecules TRIF/TRAM and downstream signalling leads to activation of 2 IKK homologs IKKε and TANK binding Kinase -1 (TBK1) which possibly form a complex together and activate transcription factors NF-κB and IFN-regulatory factor 3. From here pro inflammatory gene transcription is initiated.83 Figure 6 provides a schematic overview of intracellular TLR4 signalling.
Activation of TLR4 in renal IRI has various consequences on the graft. First of all it promotes the release of different proinflammatory mediators like IL-6, IL-1β and TNF-α, accompanied by an increased expression of macrophage inflammatory protein-2 (MIP-2) and monocyte chemo attractant protein-1 (MCP-1) involved in the recruitment of neutrophils and macrophages.82 Second,TLR4 activation leads to increased expression of adhesion molecules ICAM-1, VCAM-1 and E-selectin facilitating leukocyte migration and infiltration into the interstitial space (see above). TLR4 signalling seems mandatory for this increased expression. Chen and colleagues showed that increased expression of adhesion molecules after renal IRI was absent in TLR4 knockout mice in vivo and the addition of HMGB-1 to isolated endothelia increased adhesion molecule expression on endothelia from wild-type but not from TLR4 knockout mice.84
Thirdly, activation of TLR4 on circulating immune cells of the innate immune system leads to activation of these cells. Neutrophils and macrophages are involved in an early stage after reperfusion. Neutrophils are regarded as the primary mediators of injury and its activation leads to ROS release, secretion of different proteases and renal tissue injury.85 Upon activation macrophages release proteolytic enzymes and proinflammatory cytokines like TNF-α, IL-1β and IFN-γ.86 In TLR-4 KO mice subjected to IRI, neutrophil and macrophage infiltration was mainly reduced.82 Also natural killer (NK) cells might play an important role in renal IRI. Zhang and colleagues showed that NK cells can induce tubular cell death in vitro, possibly by interaction of retinoic acid early inducible 1 (RAE-1) on renal tubular cells and NKG2D receptor on NK cells.87 In a mouse model, they showed that NK cells quickly infiltrate into the injured kidney following I/R and that NK cell depletion was protective in this renal IRI model.87
Finally the TLR4 facilitated immune response is linked to renal fibrosis. The upregulation of TLR4 upon I/R induces a strong inflammatory response accompanied by tubular necrosis, loss of brush border, formation of casts and tubular dilatation.82 Such a robust inflammation is known to potentiate interstitial fibrosis.88
Wang and colleagues demonstrated that MyD88 and TRIF deficient mice showed a significant reduction in interstitial fibrosis reflected by reduced α-smooth muscle actin (α-SMA) and collagen I and II accumulation.89 Altogether in view of the pivotal role of TLR4 in renal IRI, inhibition of TLR4 or upstream or downstream mediators could be an interesting target in reducing IRI and optimizing graft survival.
Next to the TLR signalling the complement system plays an important role in the innate immune response in IRI. This sytem consists of soluble proteins, regulatory proteins and membrane bound receptors and comprises three pathways. DAMPs are able to activate all three pathways via binding to C1q (classical pathway), C3 (alternative pathway) or PRRs of the lectin pathway (LP). These routes have different molecular pathways but all three lead to the formation of C3-convertase
IRAK-1 IRAK-4 TRAF-6 M yD 88 TR IF NF-B NF-B Nucleus TBK-1 IRF-3 TAK-1 IKKs
MyD88 dependent pathway MyD88 independent pathway
NF-B TL R4 TL R4 DNA
Target gene expression
Figure 6. Toll like recptor 4 signaling
MyD88: Myeloid differentiation primary-response protein 88; IRAK: IL-1 receptors associated kinases; TRAF: TNF receptor associated factors; TAK-1: Transforming growth factor beta-activated kinase 1; IKKs:inhibitor of nuclear factor-κB kinase; NF-κB: nuclear factor-κB; TRIF: TIR-domain-containing adapter-inducing interferon-β; TBK-1: TANK-binding kinase 1 IRF3: Interferon regulatory factor 3
Adapted from: Zhao H, Perez JS, Lu K, George AJ, Ma D. Role of Toll-like receptor-4 in renal graft ischemia-reperfusion injury. Am J Physiol Renal Physiol. 2014; 306(8):F801-11
(C4b2b, C3bBbP). C3-convertase cleaves and activates component C3, creating C3a and C3b. C3b together with C4b2b forms C5 convertase which will cleave C5 into C5a and C5b. C5b together with C6-9 will than form the Membrane Attack Complex (MAC, C5b-9). The formed complement effectors will lead to opsonisation (C3b), chemotaxis of neutrophils and macrophages (C3a,C5a) and lysis of the cell by formation of pores in the cell membrane by the MAC.90 Under normal physiological circumstances formation of the complement effectors is controlled by proteins (soluble or surface bound) that mediate break down of the convertases C3 and C5. After I/R this balance shifts to uncontrolled complement activation leading to complement mediated injury and rejection.91 Recently the LP has been pointed out the primary route of renal complement activation after I/R.90 Activation of the LP can take place through various PRRs like collectins (manose binding lectine (MBL) and collectin-11)92, surfactant proteins (SP-A, SP-B) and ficolins (ficolin1-3)93 These PRRs interact with MBL-associated serine proteases (MASPs, MASP1-3) upon which the collectin-MASP complex is able to bind to carbohydrate bearing ligands (for instance mannose or fructose expressed on stressed cells). LP activation is critically dependant on the action of MASP-2.94,95 In an isograft transplantation model in wild type and MASP-2 deficient Chapter 2
