In Vivo Photoadduction of Anesthetic Ligands in Mouse Brain Markedly Extends Sedation and Hypnosis.

Photoaffinity ligands are best known as tools used to identify the specific binding sites of drugs to their molecular targets. However, photoaffinity ligands have the potential to further define critical neuroanatomic targets of drug action. In the brains of WT male mice, we demonstrate the feasibility of using photoaffinity ligands in vivo to prolong anesthesia via targeted yet spatially restricted photoadduction of azi-m-propofol (aziPm), a photoreactive analog of the general anesthetic propofol. Systemic administration of aziPm with bilateral near-ultraviolet photoadduction in the rostral pons, at the border of the parabrachial nucleus and locus coeruleus, produced a 20-fold increase in the duration of sedative and hypnotic effects compared with control mice without UV illumination. Photoadduction that missed the parabrachial-coerulean complex also failed to extend the sedative or hypnotic actions of aziPm and was indistinguishable from nonadducted controls. Paralleling the prolonged behavioral and EEG consequences of on target in vivo photoadduction, we conducted electrophysiologic recordings in rostral pontine brain slices. Using neurons within the locus coeruleus to further highlight the cellular consequences of irreversible aziPm binding, we demonstrate transient slowing of spontaneous action potentials with a brief bath application of aziPm that becomes irreversible on photoadduction. Together, these findings suggest that photochemistry-based strategies are a viable new approach for probing CNS physiology and pathophysiology.SIGNIFICANCE STATEMENT Photoaffinity ligands are drugs capable of light-induced irreversible binding, which have unexploited potential to identify the neuroanatomic sites of drug action. We systemically administer a centrally acting anesthetic photoaffinity ligand in mice, conduct localized photoillumination within the brain to covalently adduct the drug at its in vivo sites of action, and successfully enrich irreversible drug binding within a restricted 250 µm radius. When photoadduction encompassed the pontine parabrachial-coerulean complex, anesthetic sedation and hypnosis was prolonged 20-fold, thus illustrating the power of in vivo photochemistry to help unravel neuronal mechanisms of drug action.

Physical and Chemical Compatibility of Etomidate and Propofol Injectable Emulsions.

INTRODUCTION: The mixture of etomidate and propofol is widely used in clinical practice to improve efficacy of general anesthesia and to minimize side effects. As a thermodynamically unstable system, emulsion is prone to destabilization through mechanisms including coalescence, flocculation, and creaming. Such unwanted phenomenon can induce fat embolism after intravenous administration. This study was aimed to investigate the physical and chemical stability of the mixture of etomidate and propofol in the dosage form of emulsion. METHODS: This compatibility study focused on the critical quality attributes (CQAs) of drug-containing emulsions, such as appearance, pH, particle size and distribution, zeta potential, the observation under centrifugation, and drug content and impurity. RESULTS: As the results, there were no significant changes in the CQAs of the mixed emulsions up to 24 h after mixing at refrigeration temperature (4°C), room temperature (25°C), and body temperature (37°C). CONCLUSIONS: These results demonstrate that etomidate emulsion is physically and chemically compatible with propofol emulsions up to 24 h at 4°C, 25°C, and 37°C, suggesting that etomidate and propofol can be administrated in mixture without adversely affecting product characteristics, at least in vitro.

The effect of concentration, reconstitution solution and pH on the stability of a remifentanil hydrochloride and propofol admixture for simultaneous co-infusion.

BACKGROUND: There are scenarios where pre-mixing and infusing analgesic and anaesthetic agents as a single intravenous (IV) solution is highly desirable; however, it is important to ensure the agents are compatible when mixed. As such, the long-term stability of a remifentanil-propofol mixture, and means of improving this, were assessed across a range of remifentanil concentrations, diluents, and time points. METHODS: Remifentanil was reconstituted with ultrapure water, 0.9% saline, 20% saline, or 8.4% sodium bicarbonate solution (the latter two chosen for their pH characteristics, rather than their use in pharmaceutical reconstitution) and then mixed with propofol (1%) or further diluted with water to derive concentrations of 10-50 µg mL- 1. Remifentanil and propofol concentrations were determined initially and then periodically for up to 24 h using high performance liquid chromatography (HPLC). Mass spectrometry (MS) was used to detect degradation products in solutions containing 30 µg mL- 1 of remifentanil. Statistical analysis was performed using ANOVA and Student's t-test, with a significance value of 0.05. RESULTS: Isolated remifentanil (pH < 4) and propofol (pH 7.35) did not degrade significantly when reconstituted with water or saline solution over 24 h, while remifentanil reconstituted with sodium bicarbonate degraded significantly (P < 0.001, pH 8.65). Mixing with propofol substantially increased the pH of the mixture and resulted in significant remifentanil degradation for all reconstitution solutions used, while propofol remained stable (pH 6.50). The amount of degradation product detected in samples containing isolated remifentanil and a mixture of the drugs was proportional to the remifentanil degradation observed. CONCLUSIONS: Remifentanil stability is affected by both the reconstitution solution used and when mixed with propofol, with pH appearing to be a contributing factor to degradation. If the pH of the solution and concentration of remifentanil are correctly controlled, e.g. through the use of a more acidic diluent, an admixture of remifentanil and propofol may be useful clinically.

Remimazolam: First Approval.

Remimazolam (Anerem® in Japan; ByFavo™ in the USA; Aptimyda™ in the EU) is an ultra-short-acting intravenous (IV) benzodiazepine sedative/anesthetic being developed by PAION AG in conjunction with a number of commercial partners for use in anesthesia and procedural sedation. Remimazolam was approved on 23 January 2020 in Japan for use in general anesthesia in adult patients. Remimazolam is also undergoing regulatory assessment in South Korea for this indication and for use in procedural sedation in the USA, the EU and China. This article summarises the major milestones in the development of remimazolam for this first approval for the induction and maintenance of general anaesthesia, and its potential upcoming approvals in general anaesthesia and procedural sedation.

The role of propofol hydroxyl group in 5-lipoxygenase recognition.

Propofol is a clinically important intravenous anesthetic. We previously reported that it directly inhibited 5-lipoxygenase (5-LOX), a key enzyme for leukotriene biosynthesis. Because the hydroxyl group in propofol (propofol 1-hydroxyl) is critical for its anesthetic effect, we examined if its presence would be inevitable for 5-lipoxygenase recognition. Fropofol is developed by substituting the hydroxy group in propofol with fluorine. We found that propofol 1-hydroxyl was important for 5-lipoxygenase recognition, but it was not absolutely necessary. Azi-fropofol bound to 5-LOX at one of the two propofol binding sites of 5-LOX (pocket around Phe-187), suggesting that propofol 1-hydroxyl is important for 5-LOX inhibition at the other propofol binding site (pocket around Val-431). Interestingly, 5-hydroperoxyeicosatetraenoic acid (5-HpETE) production was significantly increased by stimulation with calcium ionophore A23187 in HEK293 cells expressing 5-LOX, suggesting that the fropofol binding site is important for the conversion from 5-HpETE to leukotriene A4. We also indicated that propofol 1-hydroxyl might have contributed to interaction with wider targets among our body.

[Climate footprint of halogenated inhalation anesthetics]. / Klimateffekterna från anestesin kan minska.

This study estimated the climate footprint of halogenated inhalation anesthetics in Sweden and estimated effects of a decreased use of these compounds. We collected data on sales of desflurane, sevoflurane and isoflurane in Sweden during 2017 and calculated the mass of CO2 equivalents (CO2e) using Global Warming Potential data over 100 years for the compounds. Inhalation anesthetics contributed by 5000 tons of CO2e which corresponds to 0.005 percent of the Swedish climate footprint. By replacing desflurane with sevoflurane the footprint can be reduced by 73 percent. By replacing sevoflurane with intravenous propofol the climate effect can be reduced further by at least 2 orders of magnitude.

Predosing Chemical Stability of Admixtures of Propofol, Ketamine, Fentanyl, and Remifentanil.

Admixtures of propofol-ketamine, propofol-ketamine-fentanyl, and propofol-ketamine-remifentanil were subjected to various clinically relevant conditions to study their chemical stability. A novel high-performance liquid chromatography-mass spectrometry method revealed no degradation of any compound by incubation at 37°C, constant mixing, or table-top storage for 6- and 24-hour time periods, except variable recovery of both propofol and fentanyl in the admixtures of propofol-ketamine-fentanyl suggesting possible degradation.

Structural Basis for a Bimodal Allosteric Mechanism of General Anesthetic Modulation in Pentameric Ligand-Gated Ion Channels.

Ion channel modulation by general anesthetics is a vital pharmacological process with implications for receptor biophysics and drug development. Functional studies have implicated conserved sites of both potentiation and inhibition in pentameric ligand-gated ion channels, but a detailed structural mechanism for these bimodal effects is lacking. The prokaryotic model protein GLIC recapitulates anesthetic modulation of human ion channels, and it is accessible to structure determination in both apparent open and closed states. Here, we report ten X-ray structures and electrophysiological characterization of GLIC variants in the presence and absence of general anesthetics, including the surgical agent propofol. We show that general anesthetics can allosterically favor closed channels by binding in the pore or favor open channels via various subsites in the transmembrane domain. Our results support an integrated, multi-site mechanism for allosteric modulation, and they provide atomic details of both potentiation and inhibition by one of the most common general anesthetics.

X-Ray Crystallographic Studies for Revealing Binding Sites of General Anesthetics in Pentameric Ligand-Gated Ion Channels.

X-ray crystallography is a powerful tool in structural biology and can offer insight into structured-based understanding of general anesthetic action on various relevant molecular targets, including pentameric ligand-gated ion channels (pLGICs). In this chapter, we outline the procedures for expression and purification of pLGICs. Optimization of crystallization conditions, especially to achieve high-resolution structures of pLGICs bound with general anesthetics, is also presented. Case studies of pLGICs bound with the volatile general anesthetic isoflurane, 2-bromoethanol, and the intravenous general anesthetic ketamine are revisited.

Structural Analysis of Anesthetics in Complex with Soluble Proteins.

Anesthetics interact with a broad range of different targets, including both soluble and membrane-bound proteins. Understanding these interactions at the molecular level requires detailed structural knowledge of anesthetic-protein complexes, and one of the most productive routes to such knowledge is X-ray crystallography. In this chapter we discuss the application of this technique to the analysis of complexes of anesthetics with soluble proteins. The model protein apoferritin is highlighted, and protocols are presented for obtaining diffraction-quality crystals of this protein in complex with different general anesthetics.

Solution NMR Studies of Anesthetic Interactions with Ion Channels.

NMR spectroscopy is one of the major tools to provide atomic resolution protein structural information. It has been used to elucidate the molecular details of interactions between anesthetics and ion channels, to identify anesthetic binding sites, and to characterize channel dynamics and changes introduced by anesthetics. In this chapter, we present solution NMR methods essential for investigating interactions between ion channels and general anesthetics, including both volatile and intravenous anesthetics. Case studies are provided with a focus on pentameric ligand-gated ion channels and the voltage-gated sodium channel NaChBac.

Possible binding sites and interactions of propanidid and AZD3043 within the γ-aminobutyric acid type A receptor (GABAAR).

Propanidid is an intravenous anesthetic with transient action and rapid recovery features, but it is clinically unacceptable due to its side effects. AZD-3043, an analog of propanidid with the methoxy group substituted by the ethoxy group, has become the focus of recent development efforts. Although propanidid and AZD-3043 are known to act by potentiating the γ-aminobutyric acid type A receptors (GABAARs), their action sites and binding modes in the recognition of target proteins still remain unclear. In this study, molecular docking and ONIOM calculations were performed to explore the possible binding sites and binding modes of propanidid and AZD-3043 with the GABAAR. The predicted active region located in the transmembrane domain (TMD) of GABAAR was identified as the most favorable binding site for propanidid and AZD-3043, with the highest docking score (-39.69 and -39.44 kcal/mol, respectively) and the largest binding energy (-88.478 and -78.439 kcal/mol, respectively). The important role of amino acids Asp245, Asp424, Asp425, Arg428, Phe307, and Ser308 in determining the binding modes of propanidid or AZD-3043 with GABAAR was revealed. The detailed molecular interactions between propanidid and AZD-3043 and the GABAAR were revealed for the first time. This could improve our understanding of the action mechanism of general anesthetics and will be helpful for the design of more potential lead-like molecules.

In silico investigation of propofol binding sites in human serum albumin using explicit and implicit solvation models.

All-atom molecular dynamics (MD) simulations are presented on general anesthetic propofol bound to human serum albumin (HSA) due to the drug pharmacokinetics and pharmacodynamics in the circulatory system. We implemented the explicit and implicit solvation models to compare the binding affinity of propofol at the different binding sites (PR1 and PR2) in the HSA protein. Only the implicit solvation models provided the evidence in accordance with the experimental data indicating that the HSA-ligand interactions are dominanted by hydrophobic forces due to the higher drug affinity at the PR1 position with a ΔGMM-PB/SA value of -23.44kcalmol-1. Overall, this study provides important information on the accuracy of explicit and implicit solvation models to characterize the propofol interaction with different HSA binding sites.

Physical Compatibility of Propofol-Sufentanil Mixtures.

BACKGROUND: Combined infusions of propofol and sufentanil preparations are frequently used in clinical practice to induce anesthesia and analgesia. However, the stability of propofol emulsions can be affected by dilution with another preparation, sometimes leading to particle coalescence and enlargement. Such unwanted effects can lead to fat embolism syndrome after intravenous application. This study describes the physical stability of 5 commercially available propofol preparations mixed with sufentanil citrate solutions. METHODS: Two common markers of emulsion stability were used in this study; namely, the zeta potential and size distribution of the emulsion droplets. Both were measured using dynamic light scattering. The data for the pure propofol preparations and their mixtures with sufentanil citrate solution were compared. RESULTS: The absolute value of zeta potential decreased in 4 of the 5 propofol preparations after they had been mixed with sufentanil citrate. This effect indicates a lowering of repulsive interactions between the emulsion droplets. Although this phenomenon tends to cause agglomeration, none of the studied mixtures displayed a substantial increase in droplet size within 24 hours of blending. However, our long-term stability study revealed the instability of some of the propofol-sufentanil samples. Two of the 5 studied mixtures displayed a continual increase in particle size. The same 2 preparations showed the greatest reductions in the absolute value of zeta potential, thereby confirming the correlation of both measurement methods. The increase in particle size was more distinct in the samples stored at higher temperatures and with higher sufentanil concentrations. CONCLUSIONS: To ensure the microbial stability of an emulsion infusion preparation, clinical regulations require that such preparations should be applied to patients within 12 hours of opening. In this respect, we can confirm that during this period, none of the studied propofol-sufentanil mixtures displayed any physical instability that could lead to particle enlargement; thus, fat embolism should not be a risk after their intravenous application. However, our long-term stability study revealed differences between commercially available preparations containing the same active ingredient; some of the mixtures showed an increase in particle size and polydispersity over a longer period. Although our results should not be generalized beyond the particular propofol-sufentanil preparations and concentrations studied here, they do suggest that, as a general principle, a compatibility study should be performed for any preparation before the first intravenous application to exclude the risk of droplet aggregation.

Characterization, in Vivo Evaluation, and Molecular Modeling of Different Propofol-Cyclodextrin Complexes To Assess Their Drug Delivery Potential at the Blood-Brain Barrier Level.

In this study, we investigated the ability of the general anesthetic propofol (PR) to form inclusion complexes with modified ß-cyclodextrins, including sulfobutylether-ß-cyclodextrin (SBEßCD) and hydroxypropyl-ß-cyclodextrin (HPßCD). The PR/SBEßCD and PR/HPßCD complexes were prepared and characterized, and the blood-brain barrier (BBB) permeation potential of the formulated PR was examined in vivo for the purpose of controlled drug delivery. The PR/SBEßCD complex was found to be more stable in solution with a minimal degradation constant of 0.25 h-1, a t1/2 of 2.82 h, and a Kc of 5.19 × 103 M-1 and revealed higher BBB permeability rates compared with the reference substance (PR-LIPURO) considering the calculated brain-to-blood concentration ratio (logBB) values. Additionally, the diminished PR binding affinity to SBEßCD was confirmed in molecular dynamics simulations by a maximal Gibbs free energy of binding (ΔGbind = -18.44 kcal·mol-1), indicating the more rapid PR/SBEßCD dissociation. Overall, the results demonstrated that SBEßCD has the potential to be used as a prospective candidate for drug delivery vector development to improve the pharmacokinetic and pharmacodynamic properties of general anesthetic agents at the BBB level.

The role of etomidate as an anaesthetic induction agent for critically ill patients.

Etomidate is an anaesthetic induction agent which may be favoured in critically ill patients because of its cardiovascular stability. However, etomidate causes adrenocortical suppression which may be particularly harmful in these patients. This article reviews current evidence and debates the use of etomidate in critical illness.

Remifentanil and propofol undergo separation and layering when mixed in the same syringe for total intravenous anesthesia.

BACKGROUND: Propofol and remifentanil can be combined to deliver total intravenous anesthesia (TIVA). Propofol and remifentanil are sometimes mixed in the same syringe. Since remifentanil is a solution and propofol is an emulsion, we hypothesized that they would separate over time when mixed in the same syringe. METHODS: Nine 60-ml polypropylene syringes were prepared as follows: Group A: 1.25 ml of remifentanil solution (1 mg·ml(-1) ) was added to 48.75 ml of propofol (10 mg·ml(-1) ) in three syringes. Group B: 2.5 ml of remifentanil (1 mg·ml(-1) ) was added to 47.5 ml of propofol (10 mg·ml(-1) ) in three syringes. Group C: 5 ml of remifentanil (1 mg·ml(-1) ) was added to 45 ml of propofol (10 mg·ml(-1) ) in three syringes. The remifentanil lyophilized powder was reconstituted with sterile water and added to the propofol by injection through the port on the bottom of the syringe. The syringe was then inverted five times in succession to mix the drugs. The syringes were mounted in an upright vertical position (plunger on top, port on bottom) with wire on a pegboard. Samples of the mixture were taken from the bottom port (via a 3-way stopcock) and from the top of the syringe (via a stopcock on an 18-gauge needle placed 5 mm through the plunger) at the following time intervals (min) from baseline: T0, T10, T30, T60, T120, T180, T240, T300. Remifentanil and propofol were quantified using specific and validated HPLC/MS/MS assays with automated online sample preparation. RESULTS: Concentrations of remifentanil were significantly greater at the top than the bottom of the syringes in groups A and B. Concentrations of propofol were significantly greater at the bottom than the top of the syringes in all groups. CONCLUSION: Our data indicate that remifentanil solution and propofol emulsion are immiscible: remifentanil separates from propofol and rises to the top. Thus, concentrations of remifentanil and propofol delivered to patients from the same syringe during TIVA are not those expected and cannot be reliable. Remifentanil and propofol should be administered in separate syringes when used in combination for TIVA.

Pain on propofol injection: Causes and remedies.

Pain on propofol injection (POPI) is a minor problem that all anesthetists face every day. Introduction of several new formulations and hundreds of clinical trials have failed to find its remedy with just one intervention in all patients. This article highlights the causes of POPI and interventions that are used to eliminate this pain in current practice. Relevant articles from Medline and Embase databases were searched and included in this descriptive review with the following conclusions: (1) POPI is due to irritation of venous adventitia leading to release of mediators such as kininogen from kinin cascade. (2) When two or more drugs or measures are used, the incidence of POPI decreases considerably. Hence, the approach to eliminating POPI should be multimodal. (3) Any regimen that includes a drug having local anesthetic effect combined with central sedative/analgesic and rapid injection into a large vein should definitely reduce the risk of POPI to negligible levels.

The Effectiveness and Stability of a 20% Emulsified Sevoflurane Formulation for Intravenous Use in Rats.

BACKGROUND: Halogenated volatile anesthetics can be safely and rapidly administered to animals and humans using emulsion formulations. However, they must be administered simultaneously with a high dose of lipids. Increasing the concentration of volatile anesthetics may solve this clinical issue. Moreover, careful observation is needed when the emulsion is injected because anaphylactic reactions have been reported. METHODS: We prepared a 20% sevoflurane lipid emulsion and administered it to 69 male Sprague-Dawley rats via the tail vein. The median effective dose (ED50) for the loss of righting reflex and the median lethal dose (LD50) were determined. ED50 and LD50 values were calculated using nonlinear regression, and data were fitted with a cumulative Gaussian model using GraphPad Prism. Measurements of vital signs and evaluation of the presence of adverse effects associated with continuous infusion of emulsions were verified. Stability of the emulsion was assessed by measuring particle size at 365 days and sevoflurane concentrations after opening the vial at 180 minutes. RESULTS: The ED50 and LD50 were 0.47 mL/kg (95% confidence interval [CI], 0.46-0.48) and 1.13 mL/kg (95% CI, 1.07-1.18), respectively. The therapeutic index (LD50/ED50) was 2.41 (95 CI%, 2.23-2.59), which compares favorably with therapeutic index of a fluoropolymer-based emulsion of sevoflurane, propofol, and thiopental. There were no adverse effects associated with the continuous infusion of emulsions. Particle size of the emulsion at 365 days after preparation was 78.9 ± 3.8 nm (±SD), and sevoflurane concentration at 180 minutes after opening the vial was 19.0% ± 0.6% (±SD). CONCLUSIONS: We prepared a 20% sevoflurane lipid emulsion using caprylic triglyceride (i.e., medium-chain triglyceride). In rats, this emulsion was an effective anesthetic and was not associated with adverse events. The emulsion was stable after consecutive evaluation for 365 days and for 180 minutes after the vial was opened.