Cholesterol crystal (CC) embolism (CCE) may be an under-recognized cause of acute kidney injury (AKI), especially of catheter intervention - or major surgery - related AKI. Little is known about the early events upon CCE due to lack of suitable animal models. We developed a new animal model of CCE-induced AKI to investigate the pathophysiology of vascular occlusion and tissue infarction.
Injecting a different dose of CC unilaterally into the renal artery of C57BL/6N mice resulted in a dose-dependent drop in glomerular filtration rate (GFR) and kidney injury. CCE induces diffuse arterial obstructions by forming fibrin+ crystal clots documented by histology and 3D reconstructions of vascular contrast micro-CT scans. CCE-induced territorial kidney infarction as shown by magnetic resonance imaging and such infarcts were surrounded by massive neutrophil infiltrates apparently also derived from vessels of the renal capsule (rim sign). Crystal clots stained positive for platelets, neutrophils, fibrin, and DNA.
While neutrophil depletion only has a minor contribution to crystal clots formation, kidney infarct, and GFR loss. Anticoagulants urokinase and heparin, which are used to treat patients with thromboembolic diseases such as myocardial infarction or stroke, both fully protected the mice from GFR loss and kidney infarction by preventing the formation of crystal clots or even resolving existing clot obstructions.
Recombinant DNase I was fully protective as it reduced the number of complete vascular occlusion, kidney infarct, kidney injury and reduction of GFR. In vitro studies revealed that CC induce membrane rupture and DNA release from endothelial cells, neutrophils, and platelets and that CC-induced activation of platelets induces neutrophil extracellular traps formation. CC embolism was found in 446 of 92,000 diagnostic kidney biopsies (0.5%). Thus, CC embolism activates numerous cell types to release DNA, which is a central component of crystal clot formation, vascular occlusion, and kidney infarct-related AKI.