Some individuals undergoing anesthesia and surgery will experience anesthetic-induced neurotoxicity (AiN) attributable to volatile general anesthetic agents (VGAs). AiN after exposure to VGAs can present with different phenotypes, including acute neurodegeneration, delirium, lifelong cognitive impairment in children and accelerated or even de novo neurodegeneration in the aged. Despite controversial clinical trials, the FDA, in a far-reaching response to recent data, has issued a warning on the use of VGAs in pregnant women and young children. Furthermore, the American Society of Anesthesiologists' Perioperative Brain Health Initiative has raised awareness of AiN for the aged brain. As neither the pathophysiology of AiN nor its risk factors are understood, there are neither prophylactic nor therapeutic measures. Our underlying hypothesis is that heritable factors determine the threshold for AiN vulnerability while biological and environmental variables shape its phenotype. We propose to approach AiN with a pharmacogenomic strategy in the fruit fly Drosophila melanogaster. We will use the ND2360114 strain, which is a model of Leigh syndrome (a human neurodegenerative disease caused by mutation of NDUFS8, the mammalian ortholog of ND23). Exposure of ND2360114 flies to VGAs results in four striking phenotypes: (1) young flies are equally hypersensitive to the behavioral effects of isoflurane and sevoflurane (reproducing the human phenotype), (2) middle-aged flies incur significant mortality within 24 hours after waking up from isoflurane, (3) genetic and environmental manipulations profoundly modulate mortality, and (4) phenotypically normal ND2360114/+ flies become sensitized to AiN from isoflurane at an advanced age thereby. We will use ND2360114 flies as a sensitized model of AiN with rapid, unambiguous readout. To investigate the modulatory role of genetic background on AiN, we will use genome-wide association study (GWAS) analysis to identify nucleotide polymorphisms that modify AiN in ND2360114/+ flies. To determine the scope of heterozygous mutations that increase the risk of AiN, we will screen candidate mutants in mitochondrial metabolic pathways. To identify key metabolic regulators of AiN, we will use RNA-seq under experimental conditions that result in different mortality rates. These studies are significant because exposure to VGA affects millions of people of all ages every year and concerns of AiN are widespread. Complications from exposure to anesthesia and surgery have long-lasting consequences. Considering genetic background when assessing the individual risk of AiN is a step towards personalized medicine. Understanding its pathophysiology offers a path to informed prevention and treatment.
The proposed research is relevant to public health because anesthetic-induced neurotoxicity (AiN) will affect a substantial number of the 20 million individuals in the US exposed to general anesthetics (GAs) every year. We propose to use a multipronged genetic strategy in a fruit fly (Drosophila melanogaster) model of AiN to identify pathways and genes that mediate AiN as well as genetic backgrounds and environmental conditions that modify the risk. The long-term goals are personalized risk assessment and informed treatment options.
