Interplay Between Nitric Oxide, Heme Oxygenase-1, and Endothelin-1 in Renal Ischemic Postconditioning: Protective Mechanisms in Neonatal Acute Kidney Injury

Ischemia-reperfusion (IR) injury is a leading cause of acute kidney injury (AKI) in infants, occurring in various clinical contexts such as sepsis, cardiopulmonary bypass, shock, and kidney transplantation. Ischemic postconditioning (IPostC) is a promising therapeutic strategy involving brief cycles of ischemia and reperfusion following a prolonged ischemic event. However, its impact on immature kidneys remains poorly understood. Nitric oxide (NO) and endothelin-1 (ET-1) serve as key opposing regulators of renal vascular tone, with NO promoting vasodilation and ET-1 inducing vasoconstriction. Beyond its role as a potent vasodilator, NO also acts as an inducer of heme oxygenase-1 (HO-1), a crucial protective enzyme that mitigates oxidative damage and inflammation. In contrast, ET-1 exacerbates renal dysfunction through its vasoconstrictive and pro-inflammatory effects. This study investigates the interplay between NO, HO-1, and ET-1 in the protective mechanisms of IPostC using a neonatal porcine model of ischemic AKI. In vitro, exposure of primary neonatal pig renal vascular endothelial cells to the NO donor NOC-18 increased HO-1 expression while suppressing ET-1 levels. In vivo, renal IR markedly decreased endothelial nitric oxide synthase (eNOS) protein expression, kidney tissue NO levels, and plasma HO-1 concentrations. However, IPostC — comprising three cycles of 5-minute reperfusion followed by 5-minute ischemia before full reperfusion — restored kidney NO levels and plasma HO-1 concentrations. IPostC also counteracted IR-induced increases in urine endothelin-converting enzyme-1 (ECE-1) and ET-1 levels, effects that were similarly achieved by the HO-1 inducer cobalt protoporphyrin (CoPP). Both IPostC and CoPP significantly preserved glomerular filtration rate and renal blood flow, reduced AKI biomarkers, and mitigated morphological kidney damage. Additionally, we found that only the ETA receptor subtype is expressed in neonatal pig renal vascular smooth muscle cells. Selective inhibition of the ET-1 pathway using either the ETA receptor antagonist sitaxentan or the ECE-1 inhibitor CGS-26303 effectively attenuated IR-induced kidney injury. Our findings suggest that: 1) Renal IR decreases NO and HO-1 levels while increasing ET-1 production; 2) IPostC restores NO levels and stimulates HO-1, thereby suppressing ET-1 biosynthesis; and 3) By promoting HO-1 and inhibiting ET-1, IPostC preserves kidney function and mitigates IR-induced AKI. In conclusion, IPostC protects against neonatal pig ischemic AKI by enhancing NO and HO-1 signaling, offering a promising therapeutic strategy to reduce kidney injury through endothelin suppression. AHA: 25POST1368875 (JED) and NIH: R01DK120595 and R01 DK127625 (AA). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.