Date Published: May 9, 2019
Publisher: Public Library of Science
Author(s): Hui Zha, Erika Matsunami, Nathan Blazon-Brown, Sophia Koutsogiannaki, Lifei Hou, Weiming Bu, Hasan Babazada, Kirsten C. Odegard, Renyu Liu, Roderic G. Eckenhoff, Koichi Yuki, Zhongcong Xie.
Perioperative infections, particularly surgical site infections pose significant morbidity and mortality. Phagocytosis is a critical step for microbial eradication. We examined the effect of commonly used anesthetics on macrophage phagocytosis and its mechanism.
The effect of anesthetics (isoflurane, sevoflurane, propofol) on macrophage phagocytosis was tested using RAW264.7 mouse cells, mouse peritoneal macrophages, and THP-1 human cells. Either opsonized sheep erythrocytes or fluorescent labeled Escherichia coli were used as phagocytic objects. The activation of Rap1, a critical protein in phagocytosis was assessed using the active Rap1 pull-down and detection kit. To examine anesthetic binding site(s) on Rap1, photolabeling experiments were performed using azi-isoflurane and azi-sevoflurane. The alanine scanning mutagenesis of Rap1 was performed to assess the role of anesthetic binding site in Rap1 activation and phagocytosis.
Macrophage phagocytosis was significantly attenuated by the exposure of isoflurane (50% reduction by 1% isoflurane) and sevoflurane (50% reduction by 1.5% sevoflurane), but not by propofol. Photolabeling experiments showed that sevoflurane directly bound to Rap1. Mutagenesis analysis demonstrated that the sevoflurane binding site affected Rap1 activation and macrophage phagocytosis.
We showed that isoflurane and sevoflurane attenuated macrophage phagocytosis, but propofol did not. Our study showed for the first time that sevoflurane served as a novel small GTPase Rap1 inhibitor. The finding will further enrich our understanding of yet-to-be determined mechanism of volatile anesthetics and their off-target effects. The sevoflurane binding site was located outside the known Rap1 functional sites, indicating the discovery of a new functional site on Rap1 and this site would serve as a pocket for the development of novel Rap1 inhibitors.
Emerging evidences suggest that surgical anesthetics possess immunomodulatory effects [1–3]. General anesthesia is mainly provided by intravenous and/or volatile anesthetics. Some patients require postoperative management in the intensive care unit (ICU) and may continue to receive sedation and pain medications. The majority of sedatives in the ICU are intravenous medications. Lately volatile anesthetics are attracting attention as ICU sedatives due to their potentially favorable profiles for pulmonary gas exchange . Perioperative infections, such as surgical site infections (SSIs), can result in significant morbidity, mortality, and financial burdens [5–8]. Therefore, it is extremely important to understand if anesthetics potentially affect the function of professional phagocytes.
In this study we found that volatile anesthetics isoflurane and sevoflurane attenuated macrophage phagocytosis via different mechanisms. The impairment by isoflurane will be explained in part by inhibiting Mac-1 as we previously reported . In addition, isoflurane might interact with molecule(s) in Rap1 signaling cascade. We found that sevoflurane directly bound to small GTPase Rap1 and attenuated its activation. Sevoflurane- Rap1 interaction was at least partly responsible for the phenotype in sevoflurane arm.