Independent pathways of P-selectin and complement-mediated renal ischemia/reperfusion injury

Post-transplant Alternative Complement Pathway Activation Influences Kidney Allograft Function

The complement system is one of the crucial pathophysiological mechanisms that directly influence the function of a transplanted kidney. Since the complement pathways’ activation potential can be easily determined via their functional activity measurement, we focused on fluctuation in the cascade activity in the early post-transplant period. The aim of the study was to relate the kidney transplantation-induced complement system response to allograft outcome. Forty-two kidney recipients (aged: 53.5 [37–52], 17 females/25 males) and 24 healthy controls (aged: 40.5 [34–51], 13 females/11 males) were enrolled in the study. The functional activities of alternative, classical, and lectin pathways were determined before and in the first week after transplantation using Wielisa^®-kit. We observed that the baseline functional activity of the alternative pathway (AP) was higher in chronic kidney disease patients awaiting transplantation compared to healthy controls and that its level depended on the type of dialysis. AP-functional activity was decreased following transplantation procedure and its post-transplant level was related to allograft function. The baseline and transplantation-induced functional activities of the classical and lectin pathways were not influenced by dialysis type and were not associated with transplant outcome. Moreover, our study showed that intraoperative graft surface cooling had a protective effect on AP activation. Our study confirms the influence of dialysis modality on persistent AP complement activation and supports the role of AP in an early phase after kidney transplantation and allograft outcome.

Endothelial colony-forming cells and pro-angiogenic cells: clarifying definitions and their potential role in mitigating acute kidney injury

Acute kidney injury (AKI) represents a significant clinical concern that is associated with high mortality rates and also represents a significant risk factor for the development of chronic kidney disease (CKD). This article will consider alterations in renal endothelial function in the setting of AKI that may underlie impairment in renal perfusion and how inefficient vascular repair may manifest post-AKI and contribute to the potential transition to CKD. We provide updated terminology for cells previously classified as 'endothelial progenitor' that may mediate vascular repair such as pro-angiogenic cells and endothelial colony-forming cells. We consider how endothelial repair may be mediated by these different cell types following vascular injury, particularly in models of AKI. We further summarize the potential ability of these different cells to mitigate the severity of AKI, improve perfusion and maintain vascular structure in pre-clinical studies.

High-resolution renal perfusion mapping using contrast-enhanced ultrasonography in ischemia-reperfusion injury monitors changes in renal microperfusion

Alterations in renal microperfusion play an important role in the development of acute kidney injury with long-term consequences. Here we used contrast-enhanced ultrasonography as a novel method for depicting intrarenal distribution of blood flow. After infusion of microbubble contrast agent, bubbles were collapsed in the kidney and postbubble destruction refilling was measured in various regions of the kidney. Local perfusion was monitored in vivo at 15, 30, 45, 60 minutes and 24 hours after 28 minutes of bilateral ischemia in 12 mice. High-resolution, pixel-by-pixel analysis was performed on each imaging clip using customized software, yielding parametric perfusion maps of the kidney, representing relative blood volume in each pixel. These perfusion maps revealed that outer medullary perfusion decreased disproportionately to the reduction in the cortical and inner medullary perfusion after ischemia. Outer medullary perfusion was significantly decreased by 69% at 60 minutes postischemia and remained significantly less (40%) than preischemic levels at 24 hours postischemia. Thus, contrast-enhanced ultrasonography with high-resolution parametric perfusion maps can monitor changes in renal microvascular perfusion in space and time in mice. This novel technique can be translated to clinical use in man.

Cardiac Sirt1 mediates the cardioprotective effect of caloric restriction by suppressing local complement system activation after ischemia-reperfusion

Caloric restriction (CR) confers cardioprotection against ischemia-reperfusion (I/R) injury. We previously found the essential roles of endothelial nitric oxide synthase in the development of CR-induced cardioprotection and Sirt1 activation during CR (Shinmura K, Tamaki K, Ito K, Yan X, Yamamoto T, Katsumata Y, Matsuhashi T, Sano M, Fukuda K, Suematsu M, Ishii I. Indispensable role of endothelial nitric oxide synthase in caloric restriction-induced cardioprotection against ischemia-reperfusion injury.Am J Physiol Heart Circ Physiol 308: H894-H903, 2015). However, the exact mechanism by which Sirt1 in cardiomyocytes mediates the cardioprotective effect of CR remains undetermined. We subjected cardiomyocyte-specific Sirt1 knockout (CM-Sirt1(-/-)) mice and the corresponding control mice to either 3-mo ad libitum feeding or CR (-40%). Isolated perfused hearts were subjected to 25-min global ischemia, followed by 60-min reperfusion. The recovery of left ventricle function after I/R was improved, and total lactate dehydrogenase release into the perfusate during reperfusion was attenuated in the control mice treated with CR, but a similar cardioprotective effect of CR was not observed in the CM-Sirt1(-/-)mice. The expression levels of cardiac complement component 3 (C3) at baseline and the accumulation of C3 and its fragments in the ischemia-reperfused myocardium were attenuated by CR in the control mice, but not in the CM-Sirt1(-/-)mice. Resveratrol treatment also attenuated the expression levels of C3 protein in cultured neonatal rat ventricular cardiomyocytes. Moreover, the degree of myocardial I/R injury in conventional C3 knockout (C3(-/-)) mice treated with CR was similar to that in the ad libitum-fed C3(-/-)mice, although the expression levels of Sirt1 were enhanced by CR. These results demonstrate that cardiac Sirt1 plays an essential role in CR-induced cardioprotection against I/R injury by suppressing cardiac C3 expression. This is the first report suggesting that cardiac Sirt1 regulates the local complement system during CR.

Mannan-binding lectin-associated serine protease 2 is critical for the development of renal ischemia reperfusion injury and mediates tissue injury in the absence of complement C4

Mannan-binding lectin-associated serine protease 2 (MASP-2) has been described as the essential enzyme for the lectin pathway (LP) of complement activation. Since there is strong published evidence indicating that complement activation via the LP critically contributes to ischemia reperfusion (IR) injury, we assessed the effect of MASP-2 deficiency in an isogenic mouse model of renal transplantation. The experimental transplantation model used included nephrectomy of the remaining native kidney at d 5 post-transplantation. While wild-type (WT) kidneys grafted into WT recipients (n=7) developed acute renal failure (control group), WT grafts transplanted into MASP-2-deficient recipients (n=7) showed significantly better kidney function, less C3 deposition, and less IR injury. In the absence of donor or recipient complement C4 (n=7), the WT to WT phenotype was preserved, indicating that the MASP-2-mediated damage was independent of C4 activation. This C4-bypass MASP-2 activity was confirmed in mice deficient for both MASP-2 and C4 (n=7), where the protection from postoperative acute renal failure was no greater than in mice with MASP-2 deficiency alone. Our study highlights the role of LP activation in renal IR injury and indicates that injury occurs through MASP-2-dependent activation events independent of C4.

Loss of ACE2 exacerbates murine renal ischemia-reperfusion injury

Ischemia-reperfusion (I/R) is a model of acute kidney injury (AKI) that is characterized by vasoconstriction, oxidative stress, apoptosis and inflammation. Previous studies have shown that activation of the renin-angiotensin system (RAS) may contribute to these processes. Angiotensin converting enzyme 2 (ACE2) metabolizes angiotensin II (Ang II) to angiotensin-(1–7), and recent studies support a beneficial role for ACE2 in models of chronic kidney disease. However, the role of ACE2 in models of AKI has not been fully elucidated. In order to test the hypothesis that ACE2 plays a protective role in AKI we assessed I/R injury in wild-type (WT) mice and ACE2 knock-out (ACE2 KO) mice. ACE2 KO and WT mice exhibited similar histologic injury scores and measures of kidney function at 48 hours after reperfusion. Loss of ACE2 was associated with increased neutrophil, macrophage, and T cell infiltration in the kidney. mRNA levels for pro-inflammatory cytokines, interleukin-1β, interleukin-6 and tumour necrosis factor-α, as well as chemokines macrophage inflammatory protein 2 and monocyte chemoattractant protein-1, were increased in ACE2 KO mice compared to WT mice. Changes in inflammatory cell infiltrates and cytokine expression were also associated with greater apoptosis and oxidative stress in ACE2 KO mice compared to WT mice. These data demonstrate a protective effect of ACE2 in I/R AKI.

Use of ultrasound to assess renal reperfusion and P-selectin expression following unilateral renal ischemia

Renal ischemia-reperfusion injury is a major cause of acute kidney injury that carries a high mortality rate and increases the risk of later development of hypertension and chronic kidney disease. Although mouse models have contributed much to our understanding of the mechanisms involved, studying aspects of the injury process in vivo remains technically challenging. This study validates the use of noninvasive ultrasound imaging to assess both renal perfusion and vascular adhesion molecule expression following 1-h unilateral renal ischemia in male and female mice. Pulsed-wave Doppler measurements of renal arterial blood velocity revealed renal perfusion recoveries of 56 ± 9% in male and 69 ± 10% in female mice 1 h after the commencing of reperfusion, which is similar to what we have previously published using conventional invasive methodology. At 24 h postischemia, renal perfusion was 40 ± 8% in male and 46 ± 7% in female mice, representing a further significant reduction of perfusion (P(Time) < 0.001). Using ultrasound imaging of a P-selectin-targeted contrast agent, a significant increase in vascular P-selectin protein expression was observed after 1-h reperfusion in the cortex of the postischemic compared with contralateral kidney in both male and female mice (18 ± 5 vs. 3 ± 3 intensity units in male and 30 ± 6 vs. 0 ± 4 in female mice, P(Ischemia) < 0.01). An approximately sixfold increase in P-selectin mRNA was observed ex vivo in the renal vasculature of male and female mice at this time point (P < 0.01). In conclusion, ultrasound represents an effective and noninvasive method for the measurement of both renal perfusion and vascular adhesion molecule expression in mice.

Cysteinyl leukotriene receptor antagonism alleviates renal injury induced by ischemia-reperfusion in rats

BACKGROUND

Renal inflammation has an important role in the development of ischemia-reperfusion injury of the kidney. Cysteinyl leukotrienes have been implicated in many inflammatory conditions. The aim of this study was to investigate the ability of the cysteinyl leukotriene receptor blocker, zafirlukast, to alleviate renal dysfunction and injury in a rat model of renal ischemia-reperfusion injury.

METHODS

We induced renal ischemia for 45 min, followed by 24 h reperfusion. We gave zafirlukast at a dose of 20 mg/kg/d for 3 d before ischemia-reperfusion. At the end of the reperfusion (24 h), we collected blood samples to measure blood urea nitrogen, creatinine, tumor necrosis factor-α, intercellular adhesion molecule-1, and nitrite/nitrate. We took kidney samples for histological and immunohistochemical assessment, and to measure malondialdehyde, glutathione content, and myeloperoxidase activity.

RESULTS

Induction of renal ischemia-reperfusion resulted into renal dysfunction, as indicated by elevated levels of blood urea nitrogen and serum creatinine, serum nitrite and nitrate, serum tumor necrosis factor-α, and intercellular adhesion molecule-1. An oxidative stress marker, renal malondialdehyde concentration, was increased, whereas renal reduced glutathione content was decreased. Myeloperoxidase activity, suggestive of neutrophil infiltration, was elevated in renal tissues. Histological changes confirmed these biochemical changes, as did P-selectin overexpression in renal tissues subjected to ischemia-reperfusion. Administration of zafirlukast before ischemia-reperfusion improved renal functions and reduced serum levels of nitrite and nitrate, tumor necrosis factor-α, and intercellular adhesion molecule-1, renal concentration of myeloperoxidase activity, and malondialdehyde concentration, whereas increased renal reduced glutathione concentration. Moreover, zafirlukast reduced histopathological features of tubular injury and P-selectin overexpression in both cortex and medulla.

CONCLUSIONS

These results demonstrate that zafirlukast significantly reduces the severity of ischemic acute renal failure, probably via anti-inflammatory action, reduction of neutrophil infiltration into renal tissues, and oxidative stress subsequent to an attenuation of P-selectin expression.

Selectins and Associated Adhesion Proteins in Inflammatory disorders

Inflammation is defined as the normal response of living tissue to injury or infection. It is important to emphasize two components of this definition. First, that inflammation is a normal response and, as such, is expected to occur when tissue is damaged. Infact, if injured tissue does not exhibit signs of inflammation this would be considered abnormal and wounds and infections would never heal without inflammation. Secondly, inflammation occurs in living tissue, hence there is need for an adequate blood supply to the tissues in order to exhibit an inflammatory response. The inflammatory response may be triggered by mechanical injury, chemical toxins, and invasion by microorganisms, and hypersensitivity reactions. Three major events occur during the inflammatory response: the blood supply to the affected area is increased substantially, capillary permeability is increased, and leucocytes migrate from the capillary vessels into the surrounding interstitial spaces to the site of inflammation or injury. The inflammatory response represents a complex biological and biochemical process involving cells of the immune system and a plethora of biological mediators. Cell-to-cell communication molecules such as cytokines play an extremely important role in mediating the process of inflammation. Inflammation and platelet activation are critical phenomena in the setting of acute coronary syndromes. An extensive exposition of this complex phenomenon is beyond the scope of this article (Rankin 2004).

Inhibition of TLR2 promotes graft function in a murine model of renal transplant ischemia-reperfusion injury

Toll-like receptors (TLRs) are important molecules involved in the activation of innate and subsequent development of adaptive immunity. TLRs are ligated by exogenous ligands from pathogens and by endogenous ligands released in inflammatory diseases. Activation of TLR leads to activation of NF-κB and release of proinflammatory cytokines, such as IL-6 and TNF-α. TLRs play an important role in the pathogenesis of renal diseases. Increased expression of TLRs have been associated with ischemic kidney damage, acute kidney injury, end-stage renal failure, acute renal transplant rejection, and delayed allograft function. OPN301 is a mouse anti-human TLR2 antibody that cross-reacts with mouse TLR2. We show that inhibition of TLR2 promotes graft function in an isograft model of renal transplantation. Recipient mice were treated intravenously with OPN301 before reperfusion of the transplanted kidney that had been subjected to 30 min of cold ischemia. After 5 d, the residual native kidney was removed, and renal transplant function was assessed 24 h later by measurement of blood urea nitrogen. Renal function in both saline- and isotype-treated mice was similar, with significant improvement in OPN301-treated mice (isotype-treated vs. OPN301-treated: 33.9±3.2 vs. 19.8±1.9 μM; P<0.01). The histopathological appearance corresponded with renal functional results. In OPN301-treated recipients, renal structure was well preserved, whereas in the saline-treated group, tubular injury was severe, with marked tubular thinning, epithelial shedding, cast formation and necrosis. Inhibition of TLR2 also leads to a decrease in C3d deposition, although it is unclear whether this is due directly to TLR2 inhibition or a decrease in renal inflammation. This study shows that inhibition of TLR2 with a therapeutic agent (OPN301) provides significant protection from ischemia/reperfusion injury in a model of kidney transplantation.

Targeted complement inhibitors protect against posttransplant cardiac ischemia and reperfusion injury and reveal an important role for the alternative pathway of complement activation

Ischemia reperfusion injury (IRI) is an unavoidable event during solid organ transplantation and is a major contributor to early graft dysfunction and subsequent graft immunogenicity. In a therapeutic paradigm using targeted complement inhibitors, we investigated the role of complement, and specifically the alternative pathway of complement, in IRI to heart isografts. Mouse heterotopic isograft heart transplants were performed in C57BL/6 mice treated with a single injection of either CR2-Crry (inhibits all complement pathways) or CR2-fH (inhibits alternative complement pathway) immediately posttransplantation. Transplanted hearts were harvested at 12 and 48 h for analysis. Both inhibitors resulted in a significant reduction in myocardial IRI, as measured by histology and serum cardiac troponin I levels. Furthermore, compared with untreated controls, both inhibitors reduced graft complement deposition, neutrophil and macrophage infiltration, adhesion molecule expression (P-selectin, E-selectin, and I-CAM-1), and proinflammatory cytokine expression (TNF-α, IL-1β, KC, and MCP-1). The reduction in myocardial damage and cellular infiltration was not significantly different between CR2-Crry- and CR2-fH-treated mice, although adhesion molecule and cytokine levels were significantly lower in CR2-Crry-treated mice compared with CR2-fH-treated mice. In conclusion, the alternative complement pathway plays a major contributing role in myocardial IRI after heart transplantation, and local (targeted) complement inhibition has the potential to provide an effective and safe therapeutic strategy to reduce graft injury. Although total complement blockade may be somewhat more efficacious in terms of reducing inflammation, specific blockade of the alternative pathway is likely to be less immunosuppressive in an already immunocompromised recipient.

Modulation of inflammatory response by selective inhibition of cyclooxygenase-1 and cyclooxygenase-2 in acute kidney injury

OBJECTIVE AND DESIGN

This work explored the role of inhibition of cyclooxygenases (COXs) in modulating the inflammatory response triggered by acute kidney injury.

MATERIAL

C57Bl/6 mice were used.

TREATMENT

Animals were treated or not with indomethacin (IMT) prior to injury (days -1 and 0).

METHODS

Animals were subjected to 45 min of renal pedicle occlusion and sacrificed at 24 h after reperfusion. Serum creatinine and blood urea nitrogen, reactive oxygen species (ROS), kidney myeloperoxidase (MPO) activity, and prostaglandin E2 (PGE(2)) levels were analyzed. Tumor necrosis factor (TNF)-alpha, t-bet, interleukin (IL)-10, IL-1beta, heme oxygenase (HO)-1, and prostaglandin E synthase (PGES) messenger RNA (mRNA) were studied. Cytokines were quantified in serum.

RESULTS

IMT-treated animals presented better renal function with less acute tubular necrosis and reduced ROS and MPO production. Moreover, the treatment was associated with lower expression of TNF-alpha, PGE(2), PGES, and t-bet and upregulation of HO-1 and IL-10. This profile was mirrored in serum, where inhibition of COXs significantly decreased interferon (IFN)-gamma, TNF-alpha, and IL-12 p70 and upregulated IL-10.

CONCLUSIONS

COXs seem to play an important role in renal ischemia and reperfusion injury, involving the secretion of pro-inflammatory cytokines, activation of neutrophils, and ROS production. Inhibition of COX pathway is intrinsically involved with cytoprotection.

Mechanisms of disease: the complement system in renal injury--new ways of looking at an old foe

The fact that the complement system is activated during immune-complex glomerular disease has been known for nearly 50 years. Detection of complement deposition in the glomerulus using immunochemistry has become an important element of the histological analysis of renal biopsies, and is key to the diagnosis of many types of glomerulonephritis. In recent years it has become evident that complement activation is involved in the pathogenesis of other types of renal disease; complement activation is implicated in transplant injury, atypical hemolytic uremic syndrome and progressive tubulointerstitial fibrosis. Emergence of this evidence has provided insight into how these diseases develop, and has yielded useful diagnostic tools and potential targets for therapeutic intervention. Clinicians have, by using plasma-based therapies, unknowingly treated abnormalities of the complement system in renal patients for many years. Advances in antibody and protein technologies have led to the development of complement inhibitors that have been used in phase III clinical studies. More-specific agents and applications are likely to be developed over the coming years and are discussed in this Review.

The role of complement and Toll-like receptors in organ transplantation

The innate immune system not only participates in host defence but also contributes to the control of adaptive immune responses. Complement and Toll-like receptors (TLR) are key components of innate immunity. Emerging evidence suggests their activation is involved in all major aspects of transplantation. This paper reviews the current understanding of how the complement and TLR on impact transplant injury.

Complement-Dependent P-Selectin Expression and Injury following Ischemic Stroke

The mechanisms that contribute to inflammatory damage following ischemic stroke are poorly characterized, but studies indicate a role for both complement and P-selectin. In this study, we show that compared with wild-type mice, C3-deficient mice showed significant improvement in survival, neurological deficit, and infarct size at 24 h after middle cerebral artery occlusion and reperfusion. Furthermore, P-selectin protein expression was undetectable in the cerebral microvasculature of C3-deficient mice following reperfusion, and there was reduced neutrophil influx, reduced microthrombus formation, and increased blood flow postreperfusion in C3-deficient mice. We further investigated the use of a novel complement inhibitory protein in a therapeutic paradigm. Complement receptor 2 (CR2)-Crry inhibits complement activation at the C3 stage and targets to sites of complement activation. Treatment of normal mice with CR2-Crry at 30 min postreperfusion resulted in a similar level of protection to that seen in C3-deficient mice in all of the above-measured parameters. The data demonstrate an important role for complement in cerebrovascular thrombosis, inflammation, and injury following ischemic stroke. P-selectin expression in the cerebrovasculature, which is also implicated in cerebral ischemia and reperfusion injury, was shown to be distal to and dependent on complement activation. Data also show that a CR2-targeted approach of complement inhibition provides appropriate bioavailability in cerebral injury to enable complement inhibition at a dose that does not significantly affect systemic levels of serum complement activity, a potential benefit for stroke patients where immunosuppression would be undesirable due to significantly increased susceptibility to lung infection.

Leucocyte depletion improves renal function during reperfusion using an experimental isolated haemoperfused organ preservation system

Background

Leucocytes have been implicated as mediators of renal ischaemia–reperfusion injury. This study aimed to demonstrate the effect of white cells in early renal reperfusion injury using an isolated haemoperfused porcine kidney model.

Methods

After 2 h cold storage, porcine kidneys were perfused with normothermic autologous blood using an isolated organ preservation system. This was designed using cardiopulmonary bypass technology, and perfusion commenced with a circulating serum creatinine level of 1000 µmol/l. In group 1 (n = 6) a leucocyte filter was included in the circuit and in group 2 (n = 6) non-filtered blood was used.

Results

The mean(s.d.) area under the curve for serum creatinine was lower in the leucocyte-depleted experiments (1286(214) versus 2627(418); P = 0·002). Leucocyte depletion also led to improved urine output (191(75) versus 70(32) ml/h; P = 0·002) and higher creatinine clearance (10·6(2·8) versus 1·9(1·0) ml/min; P = 0·002). Renal blood flow, oxygen consumption and acid–base homeostasis were all improved by perfusion with leucocyte-depleted blood, and histological tubular damage was ameliorated.

Conclusion

These data show that the depletion of leucocytes from blood used to perfuse porcine kidneys improved postschaemic renal function, indicating that white cells play an important role in renal ischaemia–reperfusion injury.

Local extravascular pool of C3 is a determinant of postischemic acute renal failure

The third complement component (C3) is an acute phase protein that plays a central role in reperfusion injury in several organ models. To investigate the contribution of local synthesis of C3 and distinguish it from that of circulating complement mainly produced by hepatic synthesis, we employed a mouse renal isograft model. Our model demonstrated a close relationship between the extent of intrarenal expression of C3 and cold-ischemia induced injury. Ischemic C3-positive donor kidneys transplanted into C3-positive or C3-negative recipients developed widespread tissue damage and severe acute renal failure. In contrast, ischemic C3-negative isografts exhibited only mild degrees of functional and structural disturbance, even when transplanted into normal C3-positive recipients. Thus local synthesis of C3, mostly identified in the tubular epithelium, was essential for complement-mediated reperfusion damage, whereas circulating C3 had a negligible effect. Our results suggest a two-compartment model for the pathogenic function of C3, in which the extravascular compartment is the domain of local synthesis of C3, and where the role of circulating C3 is redundant. Our data cast new light on the mechanism of complement-mediated tissue injury in nonimmunological disorders, and challenges the longstanding dogma that circulating components are the main complement effectors of extravascular tissue damage.

Therapeutic strategy with a membrane-localizing complement regulator to increase the number of usable donor organs after prolonged cold storage

A shortage of donor organs and increasing dependence on marginal grafts with prolonged ischemic times have meant that new methods are needed to prevent postischemic damage. Herein is reported a new strategy aimed to protect donor kidney from complement-mediated postischemic damage and therefore increase the number of successful transplants. Rat donor kidneys were perfused with a membrane-localizing complement regulator derived from human complement receptor type 1 (APT070) and then subjected to prolonged periods of cold storage (at 4 degrees C). A relationship was found between the duration of cold ischemia and the extent of complement-mediated tubule damage and loss of graft function. After 16 h of cold storage, APT070-treated kidneys that were transplanted into syngeneic recipients showed a significant increase in the number of surviving grafts, compared with control-treated grafts (63.6 versus 26.3%). Surviving grafts also displayed less acute tubular injury and better preservation of renal function. These results not only enhance the understanding of the mechanism by which prolonged cold ischemia reduces immediate graft survival but also provide essential information about the effectiveness of membrane-localizing complement regulator with prolonged cold storage. This could lead to more effective strategies for improving the use of severely ischemic donor organs.

Altered renal tubular expression of the complement inhibitor Crry permits complement activation after ischemia/reperfusion

Ischemia/reperfusion (I/R) of several organs results in complement activation, but the kidney is unique in that activation after I/R occurs only via the alternative pathway. We hypothesized that selective activation of this pathway after renal I/R could occur either because of a loss of complement inhibition or from increased local synthesis of complement factors. We examined the relationship between renal complement activation after I/R and the levels and localization of intrinsic membrane complement inhibitors. We found that loss of polarity of complement receptor 1-related protein y (Crry) in the tubular epithelium preceded activation of the alternative pathway along the basolateral aspect of the tubular cells. Heterozygous gene-targeted mice that expressed lower amounts of Crry were more sensitive to ischemic injury. Furthermore, inhibition of Crry expressed by proximal tubular epithelial cells in vitro resulted in alternative pathway-mediated injury to the cells. Thus, altered expression of a complement inhibitor within the tubular epithelium appears to be a critical factor permitting activation of the alternative pathway of complement after I/R. Increased C3 mRNA and decreased factor H mRNA were also detected in the outer medulla after I/R, suggesting that altered synthesis of these factors might further contribute to complement activation in this location.

Allograft rejection: effect of local synthesis of complement

The complement system is known for its ability to participate in non-specific inflammation and membrane injury as well as contributing to antigen-specific immune stimulation. In renal transplantation, the complement cascade behaves true to form in that both non-immune- and immune-mediated destruction of the renal tubules are complement dependent. What is remarkable, however, is the extent of involvement of local synthesis of complement in both of these injuries, suggesting that the extravascular tissue compartment is the domain of local synthesis, whereas the effect of circulating complement is much less. This creates a new paradigm for studying the influence of local synthesis of complement in other organ-based diseases and underlines the need for tissue-targeting strategies in successful therapeutic development.

Maladaptive role of IL-6 in ischemic acute renal failure

The role of IL-6 was investigated in murine ischemic acute renal failure. The renal pedicles were clamped for 17 min, and the mice were studied at various times after reperfusion. We found that serum IL-6 increased after murine ischemic renal injury. This increase was associated with increased IL-6 mRNA in the ischemic kidney but not in the contralateral kidney or the liver. Maximal IL-6 production occurred at 4 to 8 h and decreased to baseline by 24 h. Reperfusion of the kidney was required for IL-6 production. In situ hybridization and immunohistochemistry showed that macrophages infiltrated areas adjacent to the vascular bundles in the outer medulla within hours of reperfusion and showed that these macrophages produced IL-6 mRNA. For understanding how macrophages were stimulated to produce IL-6, an in vitro model in which S3 proximal tubular cells were injured by reactive oxygen species was set up. These injured cells released molecules that activated macrophages to produce IL-6 in vitro. IL-6 that was produced in response to renal ischemia was maladaptive because transgenic knockout of IL-6 ameliorated renal injury as measured by serum creatinine and histology. IL-6 transgenic knockout mice were lethally irradiated, and their bone marrow was reconstituted with wild-type IL-6 cells. Such bone marrow transfers abolished the protective effects of transgenic IL-6 knockout. It is concluded that macrophages infiltrate the area of the vascular bundles of the outer medulla, these macrophages produce IL-6, and this IL-6 exacerbates ischemic murine acute renal failure.

Targeted complement inhibition by C3d recognition ameliorates tissue injury without apparent increase in susceptibility to infection

Previous studies indicate a pivotal role for complement in mediating both local and remote injury following ischemia and reperfusion of the intestine. Here, we report on the use of a mouse model of intestinal ischemia/reperfusion injury to investigate the strategy of targeting complement inhibition to sites of complement activation by linking an iC3b/C3dg-binding fragment of mouse complement receptor 2 (CR2) to a mouse complement-inhibitory protein, Crry. We show that the novel CR2-Crry fusion protein targets sites of local and remote (lung) complement activation following intestinal ischemia and reperfusion injury and that CR2-Crry requires a 10-fold lower dose than its systemic counterpart, Crry-Ig, to provide equivalent protection from both local and remote injury. CR2-Crry has a significantly shorter serum half-life than Crry-Ig and, unlike Crry-Ig, had no significant effect on serum complement activity at minimum effective therapeutic doses. Furthermore, the minimum effective dose of Crry-Ig significantly enhanced susceptibility to infection in a mouse model of acute septic peritonitis, whereas the effect of CR2-Crry on susceptibility to infection was indistinguishable from that of PBS control. Thus, compared with systemic inhibition, CR2-mediated targeting of a complement inhibitor of activation improved bioavailability, significantly enhanced efficacy, and maintained host resistance to infection.

Inhibition of the chemokine receptor CXCR2 prevents kidney graft function deterioration due to ischemia/reperfusion

BACKGROUND

Ischemia/reperfusion (I/R) injury after organ transplantation is a major cause of delayed graft function. Following I/R, locally produced CXC chemokines attract and activate granulocytes, which in turn promote graft damage.

METHODS

We examined the involvement of granulocyte recruitment via the CXCR2 pathway in a rat model of 4 hours cold ischemia followed by kidney transplantation. Serum creatinine and intragraft granulocyte infiltration were monitored in the early phase posttransplant. A CXCR2 inhibitor, repertaxin, was given to recipients before transplantation (at -24 hours or -8 hours or -2 hours), immediately before reperfusion and 2 hours later.

RESULTS

An increase of granulocyte chemoattractant CINC-1/interleukin-8 (IL-8) mRNA expression after I/R both in syngeneic and allogeneic transplantation was associated with a marked infiltration of granulocytes in renal tissue. In syngeneic transplantation, Lewis rats given 15 mg/kg repertaxin 24 hours before surgery had granulocyte graft infiltration and serum creatinine levels significantly reduced in respect to vehicle-treated animals. Intermediate effects were observed with 5 mg/kg, whereas the dose of 30 mg/kg had toxic effects. We found that reducing the pretreatment time to 8 hours before surgery was still effective. Prevention of granulocyte infiltration and serum creatinine increase was also obtained in allogeneic transplantation, when Brown Norway recipients of Lewis kidneys were given 15 mg/kg repertaxin starting 8 hours before surgery.

CONCLUSION

Repertaxin treatment of the recipient animal was effective in preventing granulocyte infiltration and renal function impairment both in syngeneic and in allogeneic settings. The possibility to modulate I/R injury in this rat model opens new perspectives for preventing posttransplant delayed graft function in humans.

Mannan-binding lectin recognizes structures on ischaemic reperfused mouse kidneys and is implicated in tissue injury

Organ damage as a consequence of ischaemia and reperfusion (I/R) is a major clinical problem in an acute renal failure and transplantation. Ligands on surfaces of endothelial cells that are exposed due to the ischaemia may be recognized by pattern recognition molecules such as mannan-binding lectin (MBL), inducing complement activation. We examined the contribution of the MBL complement pathway in a bilateral renal I/R model (45 min of ischaemia followed by 24 h of reperfusion), using transgenic mice deficient in MBL-A and MBL-C [MBL double knockout (MBL DKO)] and in wildtype (WT) mice. Kidney damages, which were evaluated by levels of blood urea nitrogen (BUN) and creatinine, showed that MBL DKO mice were significantly protected compared with WT mice. MBL DKO mice, reconstituted with recombinant human MBL, showed a dose-dependent severity of kidney injury increasing to a comparable level to WT mice. Acute tubular necrosis was evident in WT mice but not in MBL DKO mice after I/R, confirming renal damages in WT mice. MBL ligands in kidneys were observed to be present after I/R but not in sham-operated mice. C3a (desArg) levels in MBL DKO mice were decreased after I/R compared with that in WT mice, indicating less complement activation that was correlated with less C3 deposition in the kidneys of MBL DKO mice. Our data implicate a role of MBL in I/R-induced kidney injury.

Role of adhesion molecules and dendritic cells in rat hepatic/renal ischemia-reperfusion injury and anti-adhesive intervention with anti-P-selectin lectin-EGF domain monoclonal antibody

AIM: To investigate the role of P-selectin, intercellular adhesion molecule-1 (ICAM-1) and dendritic cells (DCs) in liver/kidney of rats with hepatic/renal ischemia-reperfusion injury and the preventive effect of anti-P-selectin lectin-EGF domain monoclonal antibody (anti-PsL-EGFmAb) on the injury.

METHODS: Rat models of hepatic and renal ischemia-reperfusion were established. The rats were then divided into two groups, one group treated with anti-PsL-EGFmAb (n = 20) and control treated with saline (n = 20). Both groups were subdivided into four groups according to reperfusion time (1, 3, 6 and 24 h). The sham-operated group (n = 5) served as a control group. DCs were observed by the microscopic image method, while P-selectin and ICAM-1 were analyzed by immunohistochemistry.

RESULTS: P-selectin increased significantly in hepatic sinusoidal endothelial cells and renal tubular epithelial cells 1 h after ischemia-reperfusion, and the expression of ICAM-1 was up-regulated in hepatic sinusoid and renal vessels after 6 h. CD1a⁺CD80⁺DCs gradually increased in hepatic sinusoidal endothelium and renal tubules and interstitium 1 h after ischemia-reperfusion, and there was the most number of DCs in 24-h group. The localization of DCs was associated with rat hepatic/renal function. These changes became less significant in rats treated with anti-PsL-EGFmAb.

CONCLUSION: DCs play an important role in immune pathogenesis of hepatic/renal ischemia-reperfusion injury. Anti-PsL-EGFmAb may regulate and inhibit local DC immigration and accumulation in liver/kidney.