Inhibition of 20-HETE synthesis and action protects the kidney from ischemia/reperfusion injury

Abstract

20-Hydroxyeicosatetraenoic acid (20-HETE) production is increased in ischemic kidney tissue and may contribute to ischemia/reperfusion (I/R) injury by mediating vasoconstriction and inflammation. To test this hypothesis, uninephrectomized male Lewis rats were exposed to warm ischemia following pretreatment with either an inhibitor of 20-HETE synthesis (HET0016), an antagonist (20-hydroxyeicosa-6(Z),15(Z)-dienoic acid), an agonist (20-hydroxyeicosa-5(Z),14(Z)-dienoic acid), or vehicle via the renal artery and the kidneys were examined 2 days after reperfusion. Pretreatment with either the inhibitor or the antagonist attenuated I/R-induced renal dysfunction as shown by improved creatinine clearance and decreased plasma urea levels, compared to controls. The inhibitor and antagonist also markedly reduced tubular lesion scores, inflammatory cell infiltration, and tubular epithelial cell apoptosis. Administering the antagonist accelerated the recovery of medullary perfusion, as well as renal medullary and cortical re-oxygenation, during the early reperfusion phase. In contrast, the agonist did not improve renal injury and reversed the beneficial effect of the inhibitor. Thus, 20-HETE generation and its action mediated kidney injury due to I/R. Whether or not these effects are clinically important will need to be tested in appropriate human studies.

Figure 1. Ischemia/reperfusion (I/R)-induced release of 20-hydroxyeicosatetraenoic acid (20-HETE)

(a) In isolated perfused kidneys, I/R induced an increased release of 20-HETE that was partially blocked by HET0016. Data are given as mean ± s.e.m. (n = 6 per group). ^#P<0.05 vs basal 20-HETE release 5 min before ischemia; *P<0.05 for vehicle vs HET0016. (b) In uninephrectomized Lewis rats, 45 min of warm ischemia induced increased renal levels of free 20-HETE after pretreating the animals with vehicle (VI group) or the 20-HETE antagonist, 6,15-20-HEDE (AI group) compared with non-ischemic controls (NC group). Ischemia in the presence of HET0016 resulted in significantly lower free 20-HETE levels (HI group). Free 20-HETE levels were decreased and esterified 20-HETE levels were increased 2 h after reperfusion (groups VR, AR, and HR). Statistically significant differences with P<0.05 were observed as indicated: * = vs free 20-HETE in NC; # = vs esterified 20-HETE in NC; $ = vs free 20-HETE in VI and AI.

Figure 2. Role of 20-hydroxyeicosatetraenoic acid (20-HETE) in ischemia/reperfusion (I/R)-induced loss of renal function

Serum levels of creatinine (a) and urea (b) and the creatinine clearance (c) were determined 2 days after reperfusion. HET0016 and 6,15-20-HEDE significantly improved I/R-induced renal dysfunction, whereas 5,14-20-HEDE was not protective and partially reversed the beneficial effect of HET0016. Data are given as mean ± s.e.m. (n = 8 per group). Statistically significant differences with P<0.01 were observed as indicated: * = vs Uni-Nx, # = vs IR +vehicle, + = vs IR +5,14-20-HEDE, x = vs IR +HET0016 and y = vs IR +6,15-20-HEDE.

Figure 3. Role of 20-hydroxyeicosatetraenoic acid (20-HETE) in ischemia/reperfusion (I/R)-induced tubular injury

(a) Representative images of hematoxylin- and eosin-stained sections of the outer medulla of kidneys harvested from the different treatment groups 2 days after inducing renal I/R injury. Original magnification 100×. (b, c) Evaluation of tubular necrosis in the outer medulla and renal cortex using an acute tubular necrosis (ATN) score. HET0016 and 6,15-20-HEDE significantly ameliorated tubular damage, whereas 5,14-20-HEDE was not protective. Significant differences with P<0.05 were observed as indicated: # = vs IR +vehicle, + = vs IR +5,14-20-HEDE, x = vs IR +HET0016 and y = vs IR +6,15-20-HEDE.

Figure 4. Role of 20-hydroxyeicosatetraenoic acid (20-HETE) in ischemia/reperfusion (I/R)-induced apoptosis of tubular epithelial cells

(a) Representative images of outer medullary sections stained using the TdT-mediated dUTP nick end labeling assay to evaluate the presence of apoptotic nuclei. Original magnification 400×. (b, c) Quantification of apoptosis in the outer medulla and renal cortex by counting the percentage of apoptotic cells per high power view field. HET0016 and 6,15-20-HEDE significantly protected against I/R-induced apoptosis, whereas 5,14-20-HEDE did not. 5,14-20-HEDE significantly reversed the antiapoptotic effect of HET0016. Significant differences with P<0.01 were observed as indicated: * = vs Uni-Nx; # = vs IR +vehicle; + = vs IR +5,14-20-HEDE; x = vs IR +HET0016; y = vs IR +6,15-20-HEDE.

Figure 5. Role of 20-hydroxyeicosatetraenoic acid (20-HETE) in renal inflammation

(a) Representative images of outer medullary sections stained for ED1 + monocytes/macrophages to evaluate inflammatory cell infiltration as induced by renal ischemia/reperfusion (I/R) injury in the different animal groups. Original magnification 100×. (b, c) Quantification of inflammatory cell infiltration in the outer medulla and renal cortex by counting the number of ED1 + cells per high power view field (HPF). HET0016 and 6,15-20-HEDE significantly decreased I/R-induced inflammatory cell infiltration. In contrast, 5,14-20-HEDE significantly increased the inflammatory response in the outer medulla and reversed the anti-inflammatory effect of HET0016 both in the outer medulla and renal cortex. Significant differences with P<0.01 were observed as indicated: * = vs Uni-Nx; # = vs IR +vehicle; + = vs IR +5,14-20-HEDE; x = vs IR +HET0016; y = vs IR +6,15-20-HEDE.

Figure 6. Role of 20-hydroxyeicosatetraenoic acid (20-HETE) in ischemia/reperfusion (I/R)-induced renal hemodynamic changes and local tissue oxygenation

(a–c) Time course of relative changes in total renal blood flow (average baseline 2.9 ± 0.3 ml/min), local cortical Laser-flux, and local medullary Laser-flux. (d, e) Time course of local cortical pO₂ and local medullary pO₂. Renal ischemia (from time 0–45 min) was induced 5 min after pretreating the animals by intrarenal injections of vehicle or 6,15-20-HEDE followed by 2 h of reperfusion (n = 7 animals per group). Note the significantly accelerated and improved recovery of medullary perfusion (c) and of the cortical and medullary oxygenation (d and e) in the 6,15-20-HEDE compared with the vehicle-treated animals.