Ischemic renal injury is a complex syndrome; multiple cellular abnormalities cause accelerating cycles of inflammation, cellular damage, and sustained local ischemia. There is no single therapy that effectively resolves the renal damage after ischemia. However, infusions of normal adult rat renal cells have been a successful therapy in several rat renal failure models. The sustained broad renal benefit achieved by relatively few donor cells led to the hypothesis that extracellular vesicles (EV, largely exosomes) derived from these cells are the therapeutic effector We now show that EV from adult rat renal tubular cells significantly improved renal function when administered intravenously 24 and 48 hours after renal ischemia in rats. Additionally, EV treatment significantly improved renal tubular damage, 4-hydroxynanoneal adduct formation, neutrophil infiltration, fibrosis, and microvascular pruning. EV therapy also markedly reduced the large renal transcriptome drift observed after ischemia. These data show the potential utility of EV to limit severe renal ischemic injury after the occurrence.

Hypoxic acute kidney injury, a major unresolved problem, initiates, or aggravates, renal functional and structural decline. There is no treatment for hypoxic acute renal injury and its sequelae. We tested the hypothesis that human kidney tubular cells, or their extracellular vesicles (exosomes), prevent renal injury when infused intravenously 24 hours after 50 minutes of bilateral renal ischemia in Nude rats. Cells and their exosomes were from harvested human kidneys declined for transplantation. Injections of either cells or exosomes, given after 24 and 48 hours of reperfusion, preserved renal function and structure in both treatment groups. However, exosomes were superior to cells; and maintained renal vascular and epithelial networks, prevented renal oxidant stress, and apoptosis; and restrained activation of pro-inflammatory and pro-fibrogenic pathways. Exosomes worked in 24 hours, consistent with functional rather than regenerative activity. Comprehensive proteomic analysis identified 6152 renal proteins from all cellular compartments; and 628 were altered by ischemia at all cell levels, while 377 were significantly improved by exosome infusions. We conclude that renal damage from severe ischemia was broad, and human renal exosomes prevented most protein alterations. Thus, exosomes seem to acutely correct a critical and consequential abnormality during reperfusion. In their absence, renal structure and cells transition to a chronic state of fibrosis and extensive renal cell loss.

Ischemic acute kidney injury (AKI) is common, deadly, and accelerates progression of chronic kidney disease (CKD), yet has not specific therapy. After ischemia, reperfusion is patchy with early and persistent impairment in regional renal blood flow and cellular injury. We tested the hypothesis that intrarenal coagulation results in sustained renal ischemia following reperfusion, using a well-characterized model. Markedly decreased, but heterogeneous, microvascular plasma flow with microthrombi was found postischemia by intravital microscopy. Widespread tissue factor expression and fibrin deposition were also apparent. Clotting was accompanied by complement activation and inflammation. Treatment with exosomes derived from renal tubular cells or with the fibrinolytic urokinase, given 24 hours postischemia after renal failure was established, improved microvascular flow, coagulation, serum creatinine and histological evidence of injury. These data support the hypothesis that intrarenal clotting occurs early and the resultant sustained ischemia is a critical determinant of renal failure following ischemia; they demonstrate that the coagulation abnormalities are amenable to therapy and that therapy results in improvement in both function and postischemic inflammation.

Mortality in acute kidney injury (AKI) remains unacceptably high, yet the cause of death is commonly related to dysfunction of extra-renal organs. We and others have observed remote organ abnormalities after renal ischemia. The term cardiorenal syndrome was first applied to the "crosstalk" between the organs by the National Heart, Lung and Blood Institute of the National Institutes of Health and the clinical importance is increasingly appreciated. Nevertheless, more information is needed to effectively address the effect of renal injury on the heart. Since AKI often occurs in patients with co-morbidities, we have investigated the effect of renal ischemia in the setting of cardiac failure. We hypothesized that the cardiac effects of renal ischemia would be significantly amplified in experimental cardiomyopathy due to doxorubicin. Male Sprague-Dawley rats with preexisting cardiac and renal injury due to low dose doxorubicin were subjected to bilateral renal artery occlusion. Cardiac structure and function were examined 48 hours after reperfusion. Loss of functional myocardial tissue with decreases in left ventricular pressure, increases in apoptotic cell death, inflammation and collagen and greater disruption in ultrastructure were seen in the doxorubicin/ischemia group as compared to those animals treated with doxorubicin alone. These results suggest that preexisting co-morbidities can result in much more severe distant organ effect of acute renal injury. The results of these studies are relevant to human AKI.

Acute kidney injury (AKI) is deadly and expensive, and specific, effective therapy remains a large unmet need. We have demonstrated the beneficial effects of transplanted adult tubular cells and exosomes derived from those renal cells on experimental ischemic AKI, even when administered after renal failure is established. To further examine the mechanisms of benefit, we tested the hypothesis that exosomes from other epithelia or platelets (a rich source of exosomes) might be protective, using a well-characterized ischemia/reperfusion model. Even when given after renal failure was present, renal exosomes, but not those from skin or platelets, markedly improved renal function and histology. The differential effects allowed us to examine the mechanisms of benefit with renal exosomes. We found significant decreases in oxidative stress postischemia in the renal exosome treated group with preservation of renal superoxide dismutase and catalase. In addition, we propose a novel mechanism of benefit: renal exosomes enhanced nascent peptide synthesis following hypoxia in cells and in postischemic kidneys. Although exosomes have been used therapeutically, these results serve as "proof of principle," to examine mechanisms of injury and protection.