Abstract 551: Inhibition of Sphingosine-1-phosphate Receptor 2 Activation Protects against Renal Ischemia-Reperfusion Injury via Reduction of Reactive Oxygen Species

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Abstract

Sphingosine-1-phosphate (S1P) is a potent vasoconstrictor of the preglomerular microvasculature. Our recent studies indicate that S1P-mediated afferent arteriolar vasoconstriction is enhanced in ischemia-reperfusion (IR) induced renal injury and S1P2 receptor protein expression is increased in renal microvessels. Reactive oxygen species (ROS) play a critical role in the development of IR renal injury. We hypothesized that inhibition of S1P2 receptor activation protects against renal IR injury via ROS reduction. Renal IR injury was induced by bilateral renal artery occlusion for 60 min followed by 24 hrs reperfusion. In some rats, IR was induced during treatment with the selective S1P2 receptor antagonist, JTE-013 (0.1mg/kg BW, IP) prior to ischemia and repeated at the time of reperfusion. After reperfusion, plasma was collected and kidneys were harvested for histological analysis and ROS detection. Plasma creatinine (Cr) concentration was markedly increased in IR rats (4.2±0.1 mg/dl, n=6) compared to sham controls (1.1±0.1 mg/dl, n=5, p<0.05). JTE-013 treatment (n=4) significantly reduced plasma Cr in IR rats (2.0±0.3 mg/dl, p<0.05). Histological analysis revealed no significant cell damage in control kidney sections stained with hematoxylin and eosin whereas severe cell damage was detected in IR kidneys, including cell necrosis, disruption of the plasma membrane, nuclear pyknosis, cellular vacuolization, and the presence of luminal casts and sloughed cells in proximal tubules, particularly in the outer stripe of the outer medulla. Additionally, there was significant trapping of erythrocytes in the medulla. In contrast, JTE-013 treated IR rats showed less necrosis and cell damage in the proximal tubules. Renal ROS levels were assessed in frozen kidney sections using the fluorogenic probe, H2DCFDA. Fluorescence intensity was markedly increased in IR rats (18.7±2.4 in cortex and 19.0±2.5 in medulla) compared to control (10.9±0.7 and 9.6±0.7, p<0.05, respectively). JTE-013 treatment reduced ROS levels to values not different from control (13.5±1.1 and 15.4±1.5, p>0.05 vs. control, respectively). These data suggest that blockade of S1P2 receptors protects against renal IR injury by reducing tissue ROS accumulation.

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