Mass red blood cell extravasation and tubular uptake results in toxic injury to the tubules during kidney ischemia from venous clamping

Vascular congestion represents densely packed red blood cells (RBC) in the kidney circulation. In this study we tested the hypothesis that vascular congestion directly promotes tubular injury. All studies were performed in male and female Wistar-Kyoto rats. Vascular congestion and tubular injury were histologically examined between renal venous clamping, renal arterial clamping and venous clamping of blood free kidneys. Vessels were occluded for either 15 or 45 minutes without reperfusion. We found that venous clamping resulted in greater vascular congestion than arterial clamping, particularly in the outer-medullary region (P<0.001). Venous clamping resulted in significant tubular injury, including cell swelling, tubular necrosis and luminal cast formation following 45-minutes of occlusion. Tubular injury was significantly less following 45 minutes of arterial clamping (P<0.001). Numerous red droplets were observed within tubular cells. These were most prominent in injured cells and following venous clamping. Electron microscopy identified these droplets as RBCs and indicated that RBCs from congested renal capillaries were extravasated and taken up by tubular cells. Labelling RBCs with a cell permanent dye confirmed tubular uptake of RBCs. Demonstrating that tubular injury was due to RBC uptake, tubular injury was markedly reduced in blood free kidneys following venous clamping (P<0.001). Our data demonstrate that congestion of the kidney results in the rapid, mass extravasation and uptake of RBCs by tubular cells causing toxic injury to the tubules. Tubular toxicity from extravasation of RBCs appears to be a major component of tubular injury in ischemic AKI which has not previously been recognized. ### Competing Interest Statement The authors have declared no competing interest.