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Anesthesia, Anesthetics-Physiological effect, Anesthetics-Administration, Ischemia, Isuflurane, Microglia, Metallothionein, Neurons, Nitric oxide-Pathophysiology, Cerebrovascular disease, Zinc, Anesthetic preconditioning, Stroke, In vitro
Anesthetic preconditioning (AP) is a potential treatment for patients undergoing procedures that are accompanied by a high risk for ischemic injury (e.g. perioperative stroke) and cannot be treated by anti-coagulants. AP is a phenomenon by which tissues are pretreated with clinical concentrations of a general anesthetic; this minor insult results in the upregulation of cellular protective measures, which defend against greater insults such as ischemia. Our lab has proposed that exposure to isoflurane increases nitric oxide (NO) levels, with microglia being the major producer of NO. This triggers a downstream increase of free Zn2+, which leads to the expression of the Zn2+-binding proteins, metallothioneins (MT). To confirm increases in NO and Zn2+, microglial and neuroblastoma cell lines were exposed to the volatile anesthetic, isoflurane, at clinical concentrations. Cells were shown to produce more NO after isoflurane exposure; however, results for changes in free [Zn2+] were inconclusive. Due to the proposed role in NO production, the function of microglia in AP was tested by depleting microglia from primary neuronal and glial dissociated cultures obtained from murine brain. Microglial depletion had no effect on preconditioning but did result in attenuated cell death by oxygen glucose deprivation (OGD). The exposure of exogenous MT-IIa to cultures prior to OGD also resulted in reduced cell death in wild-type male and female MT-knockout derived cultures. Finally, to understand whether MTs exhibited protection through an extracellular receptor-mediated pathway, cultures were exposed to RAP, a competitive inhibitor of MT on megalin receptors; preliminary results are inconclusive. In summary, experiments showed that isoflurane exposure increases the level of NO in microglia, though microglia are not essential for AP. MTs exhibit protection against in vitro ischemia, but it is unclear if this is through a receptor-mediated pathway. Further understanding of this mechanism could lead to more effective administration in a clinical setting.
Ziemba, Alexis Marie, "Investigation of a molecular mechanism for anesthetic preconditioning" (2012). Honors Project, Smith College, Northampton, MA.
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