Therapeutic Targeting of Classical and Lectin Pathways of Complement Protects from Ischemia-Reperfusion-Induced Renal Damage

Ischemia-reperfusion injury is the major cause of delayed graft function in transplanted kidneys, an early event significantly affecting long-term graft function and survival. Several studies in rodents suggest that the alternative pathway of the complement system plays a pivotal role in renal ischemia-reperfusion injury. However, limited information is currently available from humans and larger animals. Here we demonstrated that 30 minutes of ischemia resulted in the induction of C4d/C1q, C4d/MLB, and MBL/MASP-2 deposits in a swine model of ischemia-reperfusion injury. The infusion of C1-inhibitor led to a significant reduction in peritubular capillary and glomerular C4d and C5b-9 deposition. Moreover, complement-inhibiting treatment significantly reduced the numbers of infiltrating CD163⁺, SWC3a⁺, CD4a⁺, and CD8a⁺ cells. C1-inhibitor administration led to significant inhibition of tubular damage and tubular epithelial cells apoptosis. Interestingly, we report that focal C4d-deposition colocalizes with C1q and MBL at the peritubular and glomerular capillary levels also in patients with delayed graft function. In conclusion, we demonstrated the activation and a pathogenic role of classical and lectin pathways of complement in a swine model of ischemia-reperfusion−induced renal damage. Therefore, inhibition of these two pathways might represent a novel therapeutic approach in the prevention of delayed graft function in kidney transplant recipients.Delayed graft function (DGF) is the primary early post-transplant complication of kidney recipients.¹ This event, histologically characterized by the presence of acute tubular necrosis, has been reported to occur in 25% to 30% of renal transplants.¹ DGF is commonly associated with a significantly longer hospital stay and an increase in peritransplant morbidity. Moreover, this early complication seems to result in a marked reduction in long-term graft survival.² Indeed, DGF is associated with an increased rate of acute rejection and a suboptimal renal function at 1-year post-transplantation.^1,2,3Ischemia followed by reperfusion plays a pivotal role in the pathogenesis of early graft damage.¹ Ischemia-reperfusion injury is characterized by two main features at the renal level: apoptosis of tubular cells and interstitial inflammation. Although many steps in the cascade of events leading to ischemia-reperfusion injury are unclear, the most promising potential mechanisms include recruitment and activation of inflammatory cells and local priming of the complement cascade.^4,5,6The complement system is a major constituent of the innate immune system, participating in the pathogenesis of tissue damage through sequential activation of different proteases. The priming of this proteolytic cascade may occur by classical, alternative, and lectin-mediated activation pathways, and generates several pro-inflammatory mediators.^6,7 Studies in animal models have shown complement activation in the kidney after ischemia-reperfusion, leading to the generation of several mediators of inflammation, such as C3a, C5a, and C5b-9.⁴ Mice deficient in complement components such as C6 show very limited damage after renal ischemia-reperfusion injury.⁸ Moreover, the use of anti-factor B or C5a-receptor antagonists has been shown to reduce renal damage due to ischemia-reperfusion.^9,10 Therefore, prevention of complement activation is currently considered one of the best therapeutic targets to prevent or limit ischemia-reperfusion−induced renal damage.^5,6,11 C1-inhibitor (C1INH) is a potent inhibitor of proteases of the classical and lectin complement pathways (C1r, C1s, and MASP2).^6,11,12 Animal studies show that C1INH can protect liver, intestine, heart, and brain tissue from ischemia-reperfusion damage.¹³ There are no published data on the effect of C1INH on ischemia-reperfusion−induced renal damage, since most of the existing evidence suggests that in this setting complement activation is mainly induced through the alternative pathway.^5,14 However, all data reported in the literature are from murine models, and no information is currently available from larger animals and/or human subjects.The aim of the present study was to investigate the pattern of complement activation in patients with DGF and to test the efficacy of a recombinant form of human C1INH (rhC1INH) in preventing renal damage in a swine model of warm ischemia-reperfusion injury.