Relief of the Renal Pressure after Ischemia-Reperfusion Injury Reduces the Inflammatory Response Within Ischemic Kidneys

Abstract

Introduction: Ischemia-reperfusion injury (I/R injury) is the most common cause of acute renal failure. In kidney transplantation, I/R injury is the primary cause of delayed graft function, which significantly decreases allograft survival. Our group has previously observed that I/R injury increases intra-renal pressure resulting in an intrinsic compartment syndrome that is characterized by impaired tubular excretion function, reduced blood flow, and structural damage to the kidney. A relief of the parenchymal pressure by a controlled capsulotomy significantly improves renal function. We currently hypothesize that an immunological aspect to this improvement exists, with the innate immune system playing a major role therein. Methods: To test this hypothesis, Balb/c wt mice were subjected to 45 min of warm renal ischemia. Parenchymal pressure was relieved by a standardized circular 0.3 mm incision at the lower pole of the kidney capsule. The ischemic as well as the non ischemic contra-lateral kidneys were harvested at 12 and 24 hours of reperfusion. The structural renal damage was assessed by histologic analysis (H&E staining). The number of infiltrating cells within the ischemic kidneys was studied using two different methods: 1.) immunhistochemistry staining for macrophages (F4/80), dendritic cells (CD11c), neutrophils (Ly6), and T cells (CD4 and CD8); 2.) isolation of cells and quantification of the above mentioned subtypes by FACS analysis. Furthermore, the inflammatory milieu within the kidneys was assessed by measuring pro-inflammatory cytokines (IL-6, IL-1b and CCL-2) by real-time PCR. The values were normalized to the expression in naïve kidneys. Discussion: Capsulotomy significantly reduced the structural damage within the ischemic kidneys. Furthermore the pro-inflammatory milieu was significantly decreased in punctured vs non-punctured kidneys with its greatest effect at 24 hours of reperfusion (IL-6: 50-fold vs 160-fold, IL-1b: 23-fold vs 45-fold, respectively). In addition, the expression of the chemokine CCL-2 was significantly reduced (4- fold vs 11-fold, respectively). Notably, F4/80+ cells were the most predominant population infiltrating ischemic kidneys, followed by CD4+ T cells and CD11c+ DC. However, capsulotomy significantly decreased CD4+ T cell (2.69-fold infiltration in non-punctured vs. punctured kidneys) as well as F4/80+ macrophage infiltration (1.46- fold infiltration in non-punctured vs. punctured kidneys) at 24 hours of reperfusion suggesting that the recruitment of cells into injured kidneys is reduced. Summary: A relief of parenchymal pressure by a controlled capsulotomy after I/R injury reduces the pro-inflammatory response within ischemic kidneys resulting in a decrease in macrophage and CD4+ T cell infiltration. Controlled capsulotomy of a kidney might therefore be a way to decrease the allogenicity of a renal donor organ before transplantation.