AKI affects both quality of life and health care costs and is an independent risk factor for mortality. At present, there are few effective treatment options for AKI. Here, we describe a nonpharmacologic, noninvasive, ultrasound-based method to prevent renal ischemia-reperfusion injury in mice, which is a model for human AKI. We exposed anesthetized mice to an ultrasound protocol 24 hours before renal ischemia. After 24 hours of reperfusion, ultrasound-treated mice exhibited preserved kidney morphology and function compared with sham-treated mice. Ultrasound exposure before renal ischemia reduced the accumulation of CD11b+Ly6Ghigh neutrophils and CD11b+F4/80high myeloid cells in kidney tissue. Furthermore, splenectomy and adoptive transfer studies revealed that the spleen and CD4+ T cells mediated the protective effects of ultrasound. Last, blockade or genetic deficiency of the α7 nicotinic acetylcholine receptor abrogated the protective effect of ultrasound, suggesting the involvement of the cholinergic anti-inflammatory pathway. Taken together, these results suggest that an ultrasound-based treatment could have therapeutic potential for the prevention of AKI, possibly by stimulating a splenic anti-inflammatory pathway.

The immune response after ischemia-reperfusion injury (IRI) contributes to tissue damage and reduced GFR. CD45+ leukocyte infiltration begins as early as 30 minutes after reperfusion, with the appearance of CD4+ and CD8+ T cells, B220+ B cells, and the myeloid/monocyte populations (including Ly6G+ neutrophils, Ly6C+CCR2+ monocytes, and F4/80+ macrophages).1,2 Attenuating this ensuing inflammatory response markedly reduces the development of IRI3–9 by preventing tubular epithelial cell apoptosis, rarefaction, and scarring.10 The severity of tissue injury depends on the duration of ischemia and results in acute loss of kidney function, progressive kidney fibrosis,11 and, in some cases, CKD or ESRD.11,12

Given the role of the innate immune system in the development of AKI,1,13,14 treatments targeting inflammation could be valuable therapeutic tools. However, current immunosuppressive agents elicit adverse effects and increase the onset of various comorbid conditions.15,16 An inherent splenic anti-inflammatory pathway has recently been described, and this pathway can be stimulated pharmacologically with nicotinic agonists or by electrical stimulation of the vagus nerve. Referred to as the cholinergic anti-inflammatory pathway, this cascade depends on the spleen, CD4+ T cells, and the α-7 nicotinic acetylcholine receptor (α7nAChR).17 This pathway modulates inflammation and benefits animals in models of myocardial ischemia,18 hepatic injury,19 sepsis and endotoxemia,17,20,21 IRI,22–24 and the response of humans injected with lipopolysaccharide.25 Because of its efficacy in humans and the preclinical data from human tissues, the cholinergic anti-inflammatory pathway is a promising therapeutic target. However, improved methods to stimulate this anti-inflammatory pathway are needed.

Using a modification of contrast-enhanced ultrasound (CEU), our original intent was to develop a method to precondition the renal vasculature before IRI.26 This concept stems from observations that a modified CEU protocol improves blood flow in ischemic skeletal muscle.27–29 Serendipitously, results from our initial studies revealed that prior ultrasound (US) exposure alone, in the absence of a contrast agent, prevented kidney IRI. Further studies indicated that the cholinergic anti-inflammatory pathway may be involved because of the dependence of the US treatment on an intact spleen and the α7nAChR. These studies provide evidence for a simple, portable, noninvasive, and nonpharmacologic approach to prevent AKI.