Evidence for the Role of Reactive Nitrogen Species in Polymicrobial Sepsis-Induced Renal Peritubular Capillary Dysfunction and Tubular Injury

Abstract

Acute kidney injury (AKI) remains a frequent and serious complication of human sepsis that contributes significantly to mortality. For better understanding of the development of AKI during sepsis, the cecal ligation and puncture (CLP) murine model of sepsis was studied using intravital video microscopy (IVVM) of the kidney. IVVM with FITC-dextran was used to determine the percentage of capillaries with continuous, intermittent or no flow at 0 (sham), 10, 16, and 22 h after CLP. There was a dramatic fall in capillary perfusion as early as 10 h after CLP that persisted through 22 h. The percentage of vessels with continuous flow at 16 h decreased from 73 ؎ 2% in shams to 16 ؎ 2% (P < 0.05), whereas the percentage of vessels with no flow increased from 4 ؎ 1% in shams to 42 ؎ 2% (P < 0.05). The capillary perfusion defect preceded the rise in serum creatinine. IVVM with dihydrorhodamine-123 was used to quantify in real time reactive nitrogen species (RNS) generation by renal tubules, and the inducible nitric oxide synthase inhibitor L-iminoethyl-lysine (mg/kg) was used to examine the role of inducible nitric oxide synthase inhibitor on capillary dysfunction and RNS generation. Tubular generation of RNS was significantly elevated at 10 h after CLP and was associated with tubules that were bordered by capillaries with reduced perfusion. L-Iminoethyl-lysine significantly reversed the capillary perfusion defect, blocked RNS generation, and reduced AKI. These data show that capillary dysfunction and RNS generation contribute to tubular injury and suggest that RNS should be considered a potential therapeutic target in the treatment of sepsis-induced AKI.

Renal Hemodynamics in AKI

“…21,26 Similarly, rodent models of acute endotoxemia suggest that cortical peritubular capillaries are among the first renal structures injured. [27][28][29][30] Interestingly, despite an apparent full recovery of renal function at 48 hours, functional capillary density recovered only partially. 27 Moreover, areas of compromised cortical microvascular perfusion have been shown to correlate with renal tubular cell stress in corresponding regions, suggesting important links between altered peritubular microcirculation and epithelial cell dysfunction.…”

“…[27][28][29][30] Interestingly, despite an apparent full recovery of renal function at 48 hours, functional capillary density recovered only partially. 27 Moreover, areas of compromised cortical microvascular perfusion have been shown to correlate with renal tubular cell stress in corresponding regions, suggesting important links between altered peritubular microcirculation and epithelial cell dysfunction. 27 These findings were corroborated by a study by Gupta et al, 31 in which quantitative two-photon intravital microscopy revealed markedly reduced peritubular capillary blood flow in an endotoxemia model in rats.…”

“…27 Moreover, areas of compromised cortical microvascular perfusion have been shown to correlate with renal tubular cell stress in corresponding regions, suggesting important links between altered peritubular microcirculation and epithelial cell dysfunction. 27 These findings were corroborated by a study by Gupta et al, 31 in which quantitative two-photon intravital microscopy revealed markedly reduced peritubular capillary blood flow in an endotoxemia model in rats. Additionally, renal ischemia and reperfusion were associated with reduced capillary blood flow and loss of glycocalyx integrity in human kidney transplantation.…”

“…Oxidative stress-mediated cellular injury has been implicated in the pathogenesis of AKI as a central element of the network of danger response, affecting both endothelial and epithelial functions as well as cellular energetics. 33 Therapeutic interventions aimed at maintaining the homeostatic balance between oxygen radicals, nitric oxide, and oxygen have been shown to be effective in several studies in rodent models of septic AKI [27][28][29][30][31] and ischemia-reperfusion injury 52 as well as in large animal models of septic AKI. 53,54 The lack of effective inducible nitric oxide synthase inhibitors for clinical use can be considered an important area for research.…”

Potential Interventions in Sepsis-Related Acute Kidney Injury

“…Molitoris (16) illustrated the phases of ischemic acute renal failure, dividing them into initiation, extension, maintenance, and recovery, and indeed this paradigm can be extended to overlap with processes in septic AKI. For instance, Wu et al (14) identified early severe reduction of peritubular capillary perfusion leading to tubular injury in a rodent cecal ligation and perforation model of sepsis using intravital videomicroscopy, but ongoing endothelial dysfunction, with loss of regulation of vascular tone, perfusion, permeability, inflammation, and adhesion, would lead to extension of this injury as proposed by Molitoris and Sutton (17) in their work on ischemic acute renal injury.…”