Oxygen and perioperative organ injury

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Project Summary/Abstract More than 20% of patients undergoing major surgery experience acute kidney, brain, and heart injury, and these perioperative complications lead to persistent organ dysfunction, long-term morbidity, and death. My research program is investigating and manipulating mechanisms of perioperative organ injury in order to identify therapeutic targets and develop novel therapies. We are currently focused on the critical impact of oxygen tension on organ injury, because perioperative oxygen administration is inconsistent, unguided, often excessive, and potentially harmful. Both hypoxia and hyperoxia can be harmful to surgical patients, yet both occur frequently, despite the ease with which the fraction of inspired oxygen (FiO2) can be manipulated in the perioperative period. Our laboratory is focused on identifying and investigating molecular pathways and therapeutic targets that a) impact oxygen tension in tissues during surgery and b) impact hypoxia- and hyperoxia-mediated organ injury. We target these molecular pathways to reduce organ injury. We have recently demonstrated that: 1) perioperative oxidative damage increases acute kidney, brain, and heart injury; 2) intraoperative normoxia improves vascular reactivity compared to hyperoxia possibly by reducing intraoperative oxidation of the heme moiety of vascular smooth muscle soluble guanylyl cyclase; 3) normoxia upregulates hypoxia inducible factor (HIF)-regulated transcription and reduces circulating markers of oxidative damage; and 4) increased circulating cell-free hemoglobin (Hb) oxidizes lipids and is independently associated with postoperative kidney, lung, and brain injury. In the next 5 years we will investigate the effects of oxygen tension on mechanisms of organ injury, including oxidative damage, vascular function, HIF signaling, and cell free Hb-mediated organ injury, using a multifaceted translational approach. Our program combines laboratory experiments in human tissues and preclinical models with prospective cohort studies and mechanistic trials in patients having major surgery. We perform experiments on arterioles and arteries isolated from patients during surgery to study the effects of hypoxic, normoxic, and hyperoxic treatments on vascular function. We investigate the impact of oxygen treatments during preclinical models of acute kidney injury in genetically engineered mice in collaboration with oxygen biologist nephrologist Volker Haase, and we are measuring the effect of intraoperative hyperoxia vs. normoxia treatment in samples biobanked from the NIGMS-supported ROCS clinical trial. Examples of these experiments include the measurement of HIF- regulated transcripts in atrial myocardium and the oxidation state of the heme group in plasma cell-free Hb. We will complement these hypothesis-driven experiments with unbiased approaches to measure the transcriptome and protein responses in vascular and murine tissues to identify and support new paths of investigation. This rigorous multimodal strategy provides the framework to advance the understanding of perioperative organ injury and guide the development of therapies for hundreds of thousands of surgical patients.