Sevoflurane depolarizes pre-synaptic mitochondria in the central nervous system

Effects of sevoflurane and its metabolite hexafluoroisopropanol on hypoxia/reoxygenation-induced injury and mitochondrial bioenergetics in murine cardiomyocytes

Background

The volatile anaesthetic sevoflurane protects cardiac tissue from reoxygenation/reperfusion. Mitochondria play an essential role in conditioning. We aimed to investigate how sevoflurane and its primary metabolite hexafluoroisopropanol (HFIP) affect necrosis, apoptosis, and reactive oxygen species formation in cardiomyocytes upon hypoxia/reoxygenation injury. Moreover, we aimed to describe the similarities in the mode of action in a mitochondrial bioenergetics analysis.

Methods

Murine cardiomyocytes were exposed to hypoxia (0.2% O2 for 6 h), followed by reoxygenation (air with 5% CO2 for 2 h) in the presence or absence sevoflurane 2.2% or HFIP 4 mM. Lactate dehydrogenase (LDH) release (necrosis), caspase activation (apoptosis), reactive oxygen species, mitochondrial membrane potential, and mitochondrial function (Seahorse XF analyser) were measured.

Results

Hypoxia/reoxygenation increased cell death by 44% (+31 to +55%, P<0.001). Reoxygenation in the presence of sevoflurane 2.2% or HFIP 4 mM increased LDH release only by +18% (+6 to +30%) and 20% (+7 to +32%), respectively. Apoptosis and reactive oxygen species formation were attenuated by sevoflurane and HFIP. Mitochondrial bioenergetics analysis of the two substances was profoundly different. Sevoflurane did not influence oxygen consumption rate (OCR) or extracellular acidification rate (ECAR), whereas HFIP reduced OCR and increased ECAR, an effect similar to oligomycin, an adenosine triphosphate (ATP) synthase inhibitor. When blocking the metabolism of sevoflurane into HFIP, protective effects of sevoflurane - but not of HFIP - on LDH release and caspase were mitigated.

Conclusion

Together, our data suggest that sevoflurane metabolism into HFIP plays an essential role in cardiomyocyte postconditioning after hypoxia/reoxygenation injury.

Involvement of Mitochondrial Dynamics and Mitophagy in Sevoflurane-Induced Cell Toxicity

General anesthesia is a powerful and indispensable tool to ensure the accomplishment of surgical procedures or clinical examinations. Sevoflurane as an inhalational anesthetic without unpleasant odor is commonly used in clinical practice, especially for pediatric surgery. However, the toxicity caused by sevoflurane has gained growing attention. Mitochondria play a key role in maintaining cellular metabolism and survival. To maintain the stability of mitochondrial homeostasis, they are constantly going through fusion and fission. Also, damaged mitochondria need to be degraded by autophagy, termed as mitophagy. Accumulating evidence proves that sevoflurane exposure in young age could lead to cell toxicity by triggering the mitochondrial pathway of apoptosis, inducing the abnormalities of mitochondrial dynamics and mitophagy. In the present review, we focus on the current understanding of mitochondrial apoptosis, dynamics and mitophagy in cell function, the implications for cell toxicity in response to sevoflurane, and their underlying potential mechanisms.

PET imaging of ischemia-induced impairment of mitochondrial complex I function in monkey brain

To assess the capability of (18)F-2-tert-butyl-4-chloro-5-{6-[2-(2-fluoroethoxy)-ethoxy]-pyridin-3-ylmethoxy}-2H-pyridazin-3-one ((18)F-BCPP-EF), a novel positron emission tomography (PET) probe for mitochondrial complex I (MC-I) activity, as a specific marker of ischemia-induced neuronal death without being disturbed by inflammation, translational research was conducted using an animal PET in ischemic brains of Cynomolgus monkeys (Macaca fascicularis). Focal ischemia was induced by the right middle cerebral artery occlusion for 3 hours, then PET scans were conducted at Day-7 with (15)O-gases for regional cerebral blood flow (rCBF) and regional cerebral metabolism of oxygen (rCMRO₂), and (18)F-BCPP-EF for MC-I with arterial blood sampling. On Day-8, the additional PET scans conducted with (11)C-flumazenil ((11)C-FMZ) for central-type benzodiazepine receptors, (11)C-PBR28 for translocator protein, and (18)F-fluoro-2-deoxy-D-glucose ((18)F-FDG) for regional cerebral metabolic rate of glucose (rCMRglc). The total distribution volume (VT) values of (18)F-BCPP-EF showed the significant reduction in MC-I activity in the damaged area at Day-7. When correlated with rCBF and rCMRO₂, the VT values of (18)F-BCPP-EF provided better correlation with rCMRO₂ than with rCBF. In the inflammatory regions (region of interest, ROIPBR) of the ischemic hemisphere detected with (11)C-PBR28, higher (18)F-FDG uptake and lower VT of (18)F-BCPP-EF, (11)C-FMZ, and rCMRO2 than those in normal contralateral hemisphere were observed. These results strongly suggested that (18)F-BCPP-EF could discriminate the neuronal damaged areas with neuroinflammation, where (18)F-FDG could not owing to its high uptake into the activated microglia.

Delayed neuroprotection induced by sevoflurane via opening mitochondrial ATP-sensitive potassium channels and p38 MAPK phosphorylation

This study aimed to investigate the role of p38 MAPK phosphorylation and opening of the mitoK(ATP) channels in the sevoflurane-induced delayed neuroprotection in the rat brain. Adult male Sprague-Dawley rats (250-300 g) were randomly assigned into four groups: ischemia/reperfusion (Control), sevoflurane (Sevo), 5-hydroxydecanoate (5-HD) + sevoflurane (5-HD + Sevo) and 5-HD groups and were subjected to right middle cerebral artery occlusion (MCAO) for 2 h. Sevoflurane preconditioning was induced 24 h before MCAO in sevoflurane and 5-HD + sevoflurane groups by exposing the animals to 2.4% sevoflurane in oxygen for 60 min. In control and 5-HD groups: animals were exposed to oxygen for 60 min at 24 h before MCAO. A selective mitoK(ATP) channel antagonist, 5-hydroxydecanoate (5-HD, 40 mg/kg, i.p.), was administered 30 min before sevoflurane/oxygen exposure in the 5-HD + sevoflurane and 5-HD groups, respectively. Neurological deficits scores and the protein expression of phosphorylated p38 mitogen-activated protein kinase (p-p38 MAPK) were evaluated at 24 and 72 h after reperfusion. Cerebral infarct size was evaluated at 72 h after reperfusion by 2,3,5-triphenyltetrazolium chloride staining. Sevoflurane preconditioning produced marked improvement neurological functions and a reduction in brain infarct volumes than animals with brain ischemia only. Sevoflurane treatment also caused increased phosphorylation of p38 MAPK at 24 and 72 h after reperfusion. These beneficial effects were attenuated by 5-HD. Blockade of cerebral protection with 5-HD concomitant with decrease in p38 phosphorylation suggests that mitoK(ATP) channels opening and p38 phosphorylation participate signal transduction cascade of sevoflurane preconditioning and p38 MAPK activation may be a downstream of opening mitoK(ATP) channels.

Pharmacologic effects on mitochondrial function

The vast majority of energy necessary for cellular function is produced in mitochondria. Free-radical production and apoptosis are other critical mitochondrial functions. The complex structure, electrochemical properties of the inner mitochondrial membrane (IMM), and genetic control from both mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) are some of the unique features that explain why the mitochondria are vulnerable to environmental injury. Because of similarity to bacterial translational machinery, mtDNA translation is likewise vulnerable to inhibition by some antibiotics. The mechanism of mtDNA replication, which is required for normal mitochondrial maintenance and duplication, is inhibited by a relatively new class of drugs used to treat AIDS. The electrochemical gradient maintained by the IMM is vulnerable to many drugs that are weak organic acids at physiological pH, resulting in excessive free-radical generation and uncoupling of oxidative phosphorylation. Many of these drugs can cause clinical injury in otherwise healthy people, but there are also examples where particular gene mutations may predispose to increased drug toxicity. The spectrum of drug-induced mitochondrial dysfunction extends across many drug classes. It is hoped that preclinical pharmacogenetic and functional studies of mitochondrial toxicity, along with personalized genomic medicine, will improve both our understanding of mitochondrial drug toxicity and patient safety.

Sevoflurane and propofol depolarize mitochondria in rat and human cerebrocortical synaptosomes by different mechanisms

BACKGROUND AND OBJECTIVES

The mitochondrial membrane potential drives the main functions of the mitochondria. Sevoflurane depolarizes neural mitochondria. There is still, however, limited information concerning the effect of anaesthetics on neural mitochondria in humans. The effect of sevoflurane and propofol on the intracellular Ca(2+) concentration [Ca(2+)](i) and the mitochondrial membrane potential (DeltaPsi(m)) was therefore compared in rat and human synaptosomes, and the changes were related to interventions in the electron transport chain.

METHODS

Synaptosomes from rat and human cerebral cortex were loaded with the fluorescent probes fura-2 ([Ca(2+)](i)) and JC-1 (DeltaPsi(m)) before exposure to sevoflurane 1 and 2 minimum alveolar concentration (MAC), and propofol 30 and 100 microM. The effect on the electron transport chain was investigated by blocking complex V.

RESULTS

Sevoflurane and propofol decreased DeltaPsi(m) in rat synaptosomes in a dose-dependent manner, and to the same extent by equipotent doses. Inhibition of complex V enhanced the depolarizing effect of sevoflurane 2 MAC, but not of propofol 100 microM. Neither sevoflurane nor propofol affected [Ca(2+)](i) significantly. Sevoflurane and propofol decreased DeltaPsi(m) in human synaptosomes to the same extent as in the rat experiments.

CONCLUSIONS

Sevoflurane and propofol at equipotent doses depolarize the mitochondria in rat and human nerve terminals to the same extent. The depolarizing effect of propofol on Psi(m) was more rapid in onset than that of sevoflurane. Whereas sevoflurane inhibits the respiratory chain sufficiently to cause ATP synthase reversal, the depolarizing effect of propofol seems to be related to inhibition of the respiratory chain from complex I to V.

Isoflurane-induced depolarization of neural mitochondria increases with age

BACKGROUND AND OBJECTIVES

The mitochondrial membrane potential (DeltaPsi(m)) drives the three fundamental functions of mitochondria, namely adenosine triphosphate (ATP) generation, Ca(2+) uptake/storage, and generation/detoxification of ROS. Isoflurane depolarizes neural mitochondria. The sensitivity for general anesthetics increases with age, but the mechanism for this age-related sensitivity is still unknown. We compared the effect of isoflurane on [Ca(2+)](i) and DeltaPsi(m) in isolated pre-synaptic terminals (synaptosomes) from neonatal, adolescent, and adult rats and the influence of interventions in the respiratory chain was assessed.

METHODS

Synaptosomes were loaded with the fluorescent probes fura-2 ([Ca(2+)](i)) and JC-1 (DeltaPsi(m)) and exposed to isoflurane 1 and 2 minimum alveolar concentration (MAC). The effect on the electron transport chain was investigated by blocking complexes I and V.

RESULTS

In neonatal rats isoflurane had no significant effect on DeltaPsi(m). In adolescent and adult synaptosomes, however, isoflurane 1 and 2 MAC decreased DeltaPsi(m). Isoflurane 2 MAC increased [Ca(2+)](i) in neonatal and adolescent rats, but not in adult synaptosomes. In Ca(2+)-depleted medium, isoflurane still decreased DeltaPsi(m), while [Ca(2+)](i) remained unaltered. By blocking complex V of the respiratory chain, the isoflurane-induced mitochondrial depolarization was enhanced in all age groups. Blocking complex I depolarized the mitochondria to the same extent as isoflurane 2 MAC, but without any additive effect.

CONCLUSIONS

The depolarizing effect of isoflurane on neural mitochondria is more pronounced in the adolescent and adult than in neonatal synaptosomes. The increased mitochondrial sensitivity with age seems to be related to the reversed function of the ATP synthase of the electron transport chain.

Physiopathological effects of the NO donor 3-morpholinosydnonimine on rat cortical synaptosomes

The NO donor 3-Morpholinosydnonimine (SIN-1) releases NO in the presence of molecular oxygen. In this study, we evaluated the effect of SIN-1 on mitochondria of rat cortical synaptosomes. We demonstrated in vitro that the amount of ONOO(-) generated and H(2)O(2) formation directly correlated with SIN-1 concentration. The mean oxygen consumption by synaptosomal mitochondria was approximately 3.8 nmol of O(2) min(-1) mg(-1) protein, which decreased significantly in the presence of SIN-1 1 mM to 2.5 nmol O(2) min(-1) mg(-1). This decrease was not modified by catalase or Trolox, demonstrating that ONOO(-) was responsible for the effect. The same concentration of SIN-1 caused a significant decrease of ATP production by synaptosomal mitochondria and depolarized the mitochondrial membrane. Moreover, ROS production increased progressively and was completely inhibited by pre-incubation of synaptosomes with Trolox. Finally, phosphatidylserine was externalized and, at the same time, intrasynaptosomal lactate dehydrogenase decreased confirming both, the external membrane breakdown after the addition of SIN-1 and the damage to the synaptosomes.

Volatile anaesthetics depolarize neural mitochondria by inhibiton of the electron transport chain

BACKGROUND

The mitochondrial membrane potential (DeltaPsim) controls the generation of adenosine triphosphate (ATP) and reactive oxygen species, and sequesteration of intracellular Ca2+[Ca2+]i. Clinical concentrations of sevoflurane affect the DeltaPsim in neural mitochondria, but the mechanisms remain elusive. The aim of the present study was to compare the effect of isoflurane and sevoflurane on DeltaPsim in rat pre-synaptic terminals (synaptosomes), and to investigate whether these agents affect DeltaPsim by inhibiting the respiratory chain.

METHODS

Synaptosomes were loaded with the fluorescent probes JC-1 (DeltaPsim) and Fura-2 ([Ca2+]i) and exposed to isoflurane or sevoflurane. The effect of the anaesthetics on the electron transport chain was investigated by blocking complex I and complex V.

RESULTS

Isoflurane 1 and 2 minimum alveolar concentration (MAC) decreased the normalized JC-1 ratio from 0.92 +/- 0.03 in control to 0.86 +/- 0.02 and 0.81 +/- 0.01, respectively, reflecting a depolarization of the mitochondrial membrane (n = 9). Isoflurane 2 MAC increased [Ca2+]i. In Ca2+-depleted medium, isoflurane still decreased DeltaPsim while [Ca2+]i remained unaltered. The effect of isoflurane was more pronounced than for sevoflurane. Blocking complex V of the respiratory chain enhanced the isoflurane- and sevoflurane-induced mitochondrial depolarization, whereas blocking complex I and V decreased DeltaPsim to the same extent in control, isoflurane and sevoflurane experiments.

CONCLUSIONS

Isoflurane and sevoflurane may act as metabolic inhibitors by depolarizing pre-synaptic mitochondria through inhibition of the electron transport chain, although isoflurane seems to inhibit mitochondrial function more significantly than sevoflurane. Both agents inhibit the respiratory chain sufficiently to cause ATP synthase reversal.

The effect of sevoflurane on intracellular calcium concentration from cholinergic cells

The mechanism of action of volatile anesthetics is not completely understood. Calcium release from internal stores may alter signaling pathways that influence neurotransmission. Abnormalities of the regulation of intracellular calcium concentration ([Ca2+]i) from patients with malignant hyperthermia is a hallmark of this syndrome indicating the potential of these agents to interact with proteins involved in Ca2+ signaling. In the present study, a cholinergic cell line (SN56) was used to examine whether the release of calcium from intracellular stores occurs in the presence of sevoflurane. Changes in [Ca2+]i were measured using fluo-4, a fluorescent calcium sensitive dye and laser scanning confocal microscopy. Sevoflurane induced an increase on [Ca2+]i from SN56 cells. The sevoflurane-induced increase on [Ca2+]i remained even when the cells were perfused with medium lacking extracellular calcium. However, this effect was abolished by BAPTA-AM, a chelator of intracellular calcium, suggesting the involvement of intracellular Ca2+ stores. Using cyclopiazonic acid, an inhibitor of sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase, we investigated whether the depletion of intracellular Ca2+ stores interfered with the effect of sevoflurane. In the presence of this agent, sevoflurane caused a small but not significant rise on [Ca2+]i of the SN56 cells. Dantrolene, an inhibitor of ryanodine-sensitive calcium stores did not modify the sevoflurane increase on [Ca2+]i. Carbachol, a drug that releases Ca2+ from the IP3 pool, abolished the effect of sevoflurane. In addition, xestospongin D, a cell-permeant IP3 receptor antagonist, decreased significantly the sevoflurane increase on [Ca2+]i. Our data suggest that the sevoflurane-induced increase on [Ca2+]i from SN56 cells occurs through the release of calcium from IP3-sensitive calcium stores.