The Serial Anesthesia Array for the High-Throughput Investigation of Volatile Agents Using <em>Drosophila melanogaster</em>

Volatile general anesthetics (VGAs) are used worldwide on millions of people of all ages and medical conditions. High concentrations of VGAs (hundreds of ...

University of Wisconsin-Madison

Genetic variability affects the response to numerous xenobiotics but its role in the clinically-observed irregular responses to general anesthetics remains uncertain. To investigate the pharmacogenetics of volatile general anesthetics (VGAs), we developed a Serial Anesthesia Array apparatus to expose multiple Drosophila melanogaster samples to VGAs and behavioral assays to determine pharmacokinetic and pharmacodynamic properties of VGAs. We studied the VGAs isoflurane and sevoflurane in four wild type strains from the Drosophila Genetic Reference Panel, two commonly used laboratory strains (Canton S and w  ), and a mutant in Complex I of the mitochondrial electron transport chain (ND23  ). In all seven strains, isoflurane was more potent than sevoflurane, as predicted by their relative lipid solubilities, and emergence from isoflurane was slower than from sevoflurane, reproducing cardinal pharmacokinetic and pharmacodynamic properties in mammals. In addition, ND23  flies were more sensitive to both agents, as observed in worms, mice, and humans carrying Complex I mutations. Moreover, we found substantial variability among the fly strains both in absolute and in relative pharmacokinetic and pharmacodynamic profiles of isoflurane and sevoflurane. These data indicate that naturally occurring genetic variations measurably influence cardinal pharmacologic properties of VGAs and that flies can be used to identify relevant genetic variations.

Genetic variability affects absolute and relative potencies and kinetics of the anesthetics isoflurane and sevoflurane in Drosophila melanogaster.

Exposure to anesthetics is common in the majority of early survivors of life-threatening injuries. Whether and to what degree general anesthetics influence outcomes from major trauma is unknown. Potential confounding effects of general anesthetics on outcome measures are usually disregarded. We hypothesized that exposure to isoflurane or sevoflurane modulates the outcome from blunt trauma with traumatic brain injury (bTBI).

Anesthetics Influence Mortality in a Drosophila Model of Blunt Trauma With Traumatic Brain Injury.

General anaesthetics interact with the pathophysiological mechanisms of traumatic brain injury (TBI). We used a Drosophila melanogaster (fruit fly) model to test the hypothesis that ageing and genetic background modulate the effect of anaesthetics and hyperoxia on TBI-induced mortality in the context of blunt trauma.

Ageing and genetic background influence anaesthetic effects in a D. melanogaster model of blunt trauma with brain injury.

General anesthetics influence mitochondrial homeostasis, placing individuals with mitochondrial disorders and possibly carriers of recessive mitochondrial mutations at increased risk of perioperative complications. In Drosophila, mutations in the ND23 subunit of complex I of the mitochondrial electron transport chain-analogous to mammalian NDUFS8-replicate key characteristics of Leigh syndrome, an inherited mitochondrial disorder. The authors used the ND23 mutant for testing the hypothesis that anesthetics have toxic potential in carriers of mitochondrial mutations.

Mitochondrial Complex I Mutations Predispose Drosophila to Isoflurane Neurotoxicity.

Following traumatic brain injury (TBI), the time window during which secondary injuries develop provides a window for therapeutic interventions. During this time, many TBI victims undergo exposure to hyperoxia and anesthetics. We investigated the effects of genetic background on the interaction of oxygen and volatile general anesthetics with brain pathophysiology after closed-head TBI in the fruit fly . To test whether sevoflurane shares genetic risk factors for mortality with isoflurane and whether locomotion is affected similarly to mortality, we used a device that generates acceleration-deceleration forces to induce TBI in ten inbred fly lines. After TBI, we exposed flies to hyperoxia alone or in combination with isoflurane or sevoflurane and quantified mortality and locomotion 24 and 48 h after TBI. Modulation of TBI-induced mortality and locomotor impairment by hyperoxia with or without anesthetics varied among fly strains and among combinations of agents. Resistance to increased mortality from hyperoxic isoflurane predicted resistance to increased mortality from hyperoxic sevoflurane but did not predict the degree of locomotion impairment under any condition. These findings are important because they demonstrate that, in the context of TBI, genetic background determines the latent toxic potentials of oxygen and anesthetics.

Interactions among Genetic Background, Anesthetic Agent, and Oxygen Concentration Shape Blunt Traumatic Brain Injury Outcomes in .

We tested the hypothesis that obesity influences the pharmacodynamics of volatile general anesthetics (VGAs) by comparing effects of anesthetic exposure on mortality from traumatic brain injury (TBI) in lean and obese  We induced TBI with a high-impact trauma device. Starvation-selection over multiple generations resulted in an obese phenotype (SS flies). Fed flies served as lean controls (FC flies). Adult (1-8-day-old) SS and FC flies were exposed to equianesthetic doses of isoflurane or sevoflurane either before or after TBI. The principal outcome was percent mortality 24 hours after injury, expressed as the Mortality Index at 24 hours (MI). TBI resulted in a lower MI in FC than in SS flies [21 (2.35) and 57.8 (2.14), respectively  = 12,  = 0.0001]. Pre-exposure to isoflurane or sevoflurane preconditioned FC flies to TBI, reducing the risk of death to 0.53 (0.25 to 1.13) and 0.82 (0.43 to 1.58), respectively, but had no preconditioning effect in SS flies. Postexposure to isoflurane or sevoflurane increased the risk of death in SS flies, but only postexposure to isoflurane increased the risk in FC flies [1.39 (0.81 to 2.38)]. Thus, obesity affects the pharmacodynamics of VGAs, thwarting the preconditioning effect of isoflurane and sevoflurane in TBI. SIGNIFICANCE STATEMENT: Inadvertent preconditioning in models of traumatic brain injury (TBI) is a recognized confounder. The findings in a fruit fly ( model of closed-head TBI indicate that anesthetic pharmacodynamics are profoundly affected by obesity. Specifically, obesity thwarts the brain-protective effect of anesthetic preconditioning. This finding is important for experimental studies of TBI and supports the versatility of the fruit fly as a model for the exploration of anesthetic pharmacodynamics in a wide parameter space.

Anesthetic Preconditioning of Traumatic Brain Injury Is Ineffective in a Drosophila Model of Obesity.

The mitochondrial electron transport chain (mETC) contains molecular targets of volatile general anesthetics (VGAs), which places carriers of mutations at risk for anesthetic complications. The  and mt: lines of fruit flies () that carry mutations in core subunits of Complex I of the mETC replicate numerous characteristics of Leigh syndrome (LS) caused by orthologous mutations in mammals and serve as models of LS.  flies are behaviorally hypersensitive to volatile anesthetic ethers and develop an age- and oxygen-dependent anesthetic-induced neurotoxicity (AiN) phenotype after exposure to isoflurane but not to the related anesthetic sevoflurane. The goal of this paper was to investigate whether the alkane volatile anesthetic halothane and other mutations in Complex I and in Complexes II-V of the mETC cause AiN. We found that (i)  and mt: were susceptible to toxicity from halothane; (ii) in wild-type flies, halothane was toxic under anoxic conditions; (iii) alleles of accessory subunits of Complex I predisposed to AiN; and (iv) mutations in Complexes II-V did not result in an AiN phenotype. We conclude that AiN is neither limited to ether anesthetics nor exclusive to mutations in core subunits of Complex I.

Zachariah P. G. Olufs

Department of Anesthesiology

University of Wisconsin-Madison

The Serial Anesthesia Array for the High-Throughput Investigation of Volatile Agents Using Drosophila melanogaster

Zachariah P. G. Olufs

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Anesthesiology

University of Wisconsin-Madison

The Serial Anesthesia Array for the High-Throughput Investigation of Volatile Agents Using Drosophila melanogaster

Department of Anesthesiology