Effects of Remimazolam and Propofol on Ca2+ Regulation by Ryanodine Receptor 1 with Malignant Hyperthermia Mutation

Remimazolam

Remimazolam is a new reversible γ-aminobutyric acid type A agonist benzodiazepine that displays a fast onset of action, short recovery time with a safe cardiopulmonary profile and favorable pharmacokinetics in comparison with other intravenous sedatives.

Propofol binds and inhibits skeletal muscle ryanodine receptor 1

BACKGROUND

As the primary Ca2+ release channel in skeletal muscle sarcoplasmic reticulum (SR), mutations in type 1 ryanodine receptor (RyR1) or its binding partners underlie a constellation of muscle disorders, including malignant hyperthermia (MH). In patients with MH mutations, triggering agents including halogenated volatile anaesthetics bias RyR1 to an open state resulting in uncontrolled Ca2+ release, increased sarcomere tension, and heat production. Propofol does not trigger MH and is commonly used for patients at risk of MH. The atomic-level interactions of any anaesthetic with RyR1 are unknown.

METHODS

RyR1 opening was measured by [3H]ryanodine binding in heavy SR vesicles (wild type) and single-channel recordings of MH mutant R615C RyR1 in planar lipid bilayers, each exposed to propofol or the photoaffinity ligand analogue m-azipropofol (AziPm). Activator-mediated wild-type RyR1 opening as a function of propofol concentration was measured by Fura-2 Ca2+ imaging of human skeletal myotubes. AziPm binding sites, reflecting propofol binding, were identified on RyR1 using photoaffinity labelling. Propofol binding affinity to a photoadducted site was predicted using molecular dynamics (MD) simulation.

RESULTS

Both propofol and AziPm decreased RyR1 opening in planar lipid bilayers (P<0.01) and heavy SR vesicles, and inhibited activator-induced Ca2+ release from human skeletal myotube SR. Several putative propofol binding sites on RyR1 were photoadducted by AziPm. MD simulation predicted propofol KD values of 55.8 μM and 1.4 μM in the V4828 pocket in open and closed RyR1, respectively.

CONCLUSIONS

Propofol demonstrated direct binding and inhibition of RyR1 at clinically plausible concentrations, consistent with the hypothesis that propofol partially mitigates malignant hyperthermia by inhibition of induced Ca2+ flux through RyR1.

Determination of ED50 and ED95 of remimazolam besylate combined with alfentanil for adult gastroscopy: a prospective dose-finding study

BACKGROUND

To explore the median effective dose (ED50) and 95% effective dose (ED95) of remimazolam besylate combined with alfentanil for adult gastroscopy.

METHODS

This prospective studyenrolled 31 patients scheduled to painless gastroscopy at Anhui No. 2 Provincial People's Hospital between April and May, 2022. 5 µg.kg-1 of alfentanil hydrochloride was used for pre-analgesia. The initial single loading dose of remimazolam besylate was 0.12 mg.kg-1, increased or reduced by 0.01 mg.kg-1 for the next patient with modified Dixon sequential method. The modified Observer's Assessment of Alertness/Sedation Scale (MOAA/S) was used to assess sedation.

RESULTS

Combined with alfentanil, the ED50 of remimazolam besylate was 0.147 mg.kg-1 (95% CI: 0.138-0.160 mg.kg-1) and ED95 0.171 mg.kg-1 (95% CI: 0.159-0.245 mg.kg-1). The induction time after injection of remimazolam besylate was 70 ± 25 s, with the anesthesia recovery time and the observation time in resuscitation room 5.13 ± 2.13 min and 2.32 ± 1.6 min, respectively. Twenty nine patients' vital signs were within acceptable limits during gastroscopy.

CONCLUSIONS

The ED50 of remimazolam besylate combined with alfentanil for painless gastroscopy was 0.147 mg.kg-1, and the ED95 was 0.171 mg.kg-1.

Remimazolam-based total intravenous anesthesia in a patient with a confirmed diagnosis of malignant hyperthermia: a case report

BACKGROUND

Malignant hyperthermia (MH) is a rare, life-threatening disorder of calcium homeostasis in skeletal muscle cells that is triggered by volatile anesthetics and succinylcholine, leading to a hypermetabolic reaction. The pathogenic ryanodine receptor 1 (RYR1) gene variant is critical. Patients susceptible to MH should avoid triggering agents, and total intravenous anesthesia (TIVA) is preferred. Remimazolam is safe in patients with suspected MH.

CASE PRESENTATION

We present the first case of remimazolam treatment in a genetically confirmed patient with MH without MH development. A 72-year-old man with a family history of MH underwent remimazolam-based TIVA. After informed consent was obtained, a muscle biopsy and genetic testing were performed. Intraoperatively and postoperatively, the patient exhibited no signs of MH. An enhanced function of the RYR1 channel into releasing calcium was indicated, and the genetic testing revealed a pathogenic variant of RYR1.

CONCLUSIONS

Remimazolam-based TIVA is safe in patients confirming the diagnosis of MH.

Clinical Application and Research Progress of Remimazolam for Pediatric Patients

Remimazolam is a novel ultrashort-acting benzodiazepine that allosterically modulates γ-aminobutyric acid type A (GABAA) receptors to exert sedative effects. Remimazolam has the properties of controllable sedation, rapid onset, and a short duration of action, along with minor depression of circulation and respiration. Remimazolam has been approved for clinical use since 2020 in Japan, and it has been applied for procedural sedation, general anesthesia induction and maintenance, and sedation in ICU patients, and has been proven to be safe and effective. Currently, no consensus has been reached on the clinical application of remimazolam in pediatric patients. This review introduces the clinical research progress and limitations of remimazolam in recent years, aiming to supply scientific guidance and a theoretical reference for the application of remimazolam in pediatric anaesthesia.

The Role of Remimazolam in Neurosurgery and in Patients With Neurological Diseases: A Narrative Review

Remimazolam is a novel ultrashort-acting benzodiazepine that produces sedation by acting as a positive allosteric modulator of the gamma-amino butyric acid-A receptor. Its high water solubility and metabolism via tissue esterases allow for a rapid onset of sedation/anesthesia and prompt arousal despite prolonged use. In addition, the effects of remimazolam can be reversed with flumazenil. This narrative review discusses the role of remimazolam in patients undergoing neurosurgical and neuroradiological procedures, specifically its role during awake craniotomies and compatibility with neuromonitoring. Considerations for remimazolam use in patients with neurological diseases are also highlighted. In addition, the impact of remimazolam on postoperative excitation, risk for postoperative delirium, and delayed neurocognitive recovery are discussed. Although there seems to be a clinical promise for remimazolam based on limited case studies and our own institutional experience of its use, further clinical investigation is warranted to understand the potential impact of remimazolam on surgical and neurological outcomes.

Effects of Remimazolam on Intracellular Calcium Dynamics in Myotubes Derived from Patients with Malignant Hyperthermia and Functional Analysis of Type 1 Ryanodine Receptor Gene Variants

Remimazolam is a novel general anesthetic and its safety in patients with malignant hyperthermia (MH) is unknown. We used myotubes derived from the skeletal muscle of patients with MH to examine the response to ryanodine receptor 1 (RYR1) agonist and remimazolam in MH-susceptible patients. Patients underwent muscle biopsy for the Ca2+-induced Ca2+ release (CICR) rate test, a diagnostic tool for MH in Japan. Ten patients had myotubes obtained from skeletal muscle cultures, and the genes associated with malignant hyperthermia in these patients were analyzed. The EC50 of caffeine, cresol, and remimazolam to induce intracellular calcium concentration change were compared between myotubes from CICR-negative genetic test patients and myotubes from other patients. Eight of the ten were CICR-positive, five of whom had RYR1 causative gene mutations or variants. Two patients had CICR-negative genetic tests, and as expected had the highest EC50 (the concentration of a drug that gives a half-maximal response) in response to caffeine, 4CmC and remimazolam. Three patients had a positive CICR but no known variants in RYR1 or CACNA1S (voltage-gated calcium channel subunit alpha1S). Myotubes in these patients had significantly lower EC50s for all agents than myotubes in CICR-negative patients. When myotubes from a patient who was CICR-negative and had no gene variant were used as a control, myotubes from CICR-positive patients were more hyper-responsive than controls to all stimulants used. The EC50 for remimazolam was lowest for myotubes from CICR-positive, RYR1-mutant patients, at 206 µM (corresponding to 123 µg/mL). The concentration was more than 80-times higher than the clinical concentration. RYR1 gene variants in R4645Q and W5020G were shown to be causative gene mutations for MH. Intracellular calcium in myotubes from MH patients are elevated at high concentrations of remimazolam but not at clinically used concentrations of remimazolam. Remimazolam appears to be safe to use in patients with MH.

Remimazolam Compared to Propofol During Hysteroscopy: A Safety and Efficacy Analysis

INTRODUCTION

Propofol is the main drug used to induce sedation for endoscopic procedures, and few drugs had shaken its dominant clinical use for a decade until the development of remimazolam. Remimazolam has been demonstrated to perform well in post-marketing studies on sedation for colonoscopy or other procedures requiring short periods of sedation. This study aimed to establish whether remimazolam was effective and safe for inducing sedation for hysteroscopy.

METHODS

One hundred patients who were scheduled to undergo hysteroscopy were randomly assigned to receive induction with remimazolam or propofol. A dose of 0.25 mg/kg remimazolam was administered. Propofol was started at 2-2.5 mg/kg. Before remimazolam or propofol induction, 1 μg/kg fentanyl was infused. Hemodynamic parameters, vital signs, and bispectral index (BIS) values were measured and adverse events recorded to evaluate safety. We comprehensively evaluated the efficacy and safety of the two drugs by the success rate of induction, fluctuation of vital signs, depth of anesthesia, adverse reactions, recovery time, and other indicators.

RESULTS

Information on 83 patients was successfully recorded and carefully documented. The success rate of sedation in the remimazolam group (group R) was 93%, which was lower than for the propofol group (group P) (100%), but there was no statistically significant difference between the two groups. The incidence of adverse reactions in group R (7.5%) was significantly lower than that in group P (67.4%), and the results were statistically significant (P < 0.01). The fluctuation of vital signs in group P was more severe after induction, especially in patients with cardiovascular diseases.

CONCLUSIONS

Remimazolam avoids the injection pain produced by propofol sedation, has a better pre-sedation experience, had the advantage of stable hemodynamics after injection compared to propofol, and a lower respiratory depression rate in the study patients.

Use of remimazolam in living donor liver transplantation: a case report

Background

Remimazolam is an intravenous ultra-short-acting benzodiazepine with the benefit of hemodynamic stability, including blood pressure and pulse rate. We report a case in which remimazolam was used in living donor liver transplantation with stable hemodynamics.

Case presentation

A 19-year-old woman underwent living donor liver transplantation due to end-stage liver disease, which is associated with a hyperdynamic state and hemodynamic instability. The patient’s sister had a history of malignant hyperthermia, so we chose total intravenous anesthesia with remimazolam. Intraoperative bleeding of seven liters occurred, but she had mild intraoperative blood pressure changes, and continuous catecholamine administration was not necessary. The patient had no memories or discomfort during the surgery.

Conclusions

We maintained stable hemodynamics using remimazolam for anesthetic management of a patient undergoing a liver transplantation, which is characterized by a hyperdynamic state and circulatory instability.

The effects of dantrolene in the presence or absence of ryanodine receptor type 1 variants in individuals predisposed to malignant hyperthermia

Dantrolene is currently the only drug known to specifically treat malignant hyperthermia (MH) crises. Although dantrolene attenuates Ca²⁺ disorders by acting mainly on the ryanodine receptor type 1 (RYR1), some patients who manifest MH without RYR1 variants have also been successfully treated with dantrolene. Thus, dantrolene appears to have an inhibitory effect on patients with and without RYR1 variants. This study aimed to investigate whether the effects of dantrolene differed depending on the presence or absence of RYR1 variants using muscle cells from MH-predisposed individuals. The study participants were individuals diagnosed with MH predisposition by the Ca²⁺-induced Ca²⁺ release rate test. They were genetically tested and divided into two groups: with and without RYR1 variants. We investigated whether these two groups showed differences in the changes in the half-maximal effective concentration (EC₅₀) for caffeine and the resting intracellular Ca²⁺ concentration ([Ca²⁺]_i) before and after dantrolene administration. Dantrolene administration significantly increased the EC₅₀ (P < 0.0001) and decreased the resting [Ca²⁺]_i (P < 0.0001). The inhibitory effects of dantrolene and the presence of RYR1 variants showed no statistically significant interactions related to the EC₅₀ (P = 0.59) and resting [Ca²⁺]_i (P = 0.21). In conclusion, the presence or absence of RYR1 variants does not appear to influence the effect of dantrolene.

Characterization of intracellular calcium mobilization induced by remimazolam, a newly approved intravenous anesthetic

Many anesthetics, including Propofol, have been reported to induce elevation of intracellular calcium, and we were interested to investigate the possible contribution of calcium elevation to the mechanism of the newly approved remimazolam actions. Remimazolam is an intravenous anesthetic first approved in Japan in July 2020, and is thought to exert its anesthetic actions via γ-aminobutyric acid A (GABAA) receptors; however, the precise mechanisms of how remimazolam elevates intracellular calcium levels remains unclear. We examined the remimazolam-induced elevation of intracellular calcium using SHSY-5Y neuroblastoma cells, COS-7 cells, HEK293 cells, HeLa cells, and human umbilical vein endothelial cells (HUVECs) loaded with fluorescent dyes for live imaging. We confirmed that high concentrations of remimazolam (greater than 300 μM) elevated intracellular calcium in a dose-dependent manner in these cells tested. This phenomenon was not influenced by elimination of extracellular calcium. The calcium elevation was abolished when intracellular or intraendoplasmic reticulum (ER) calcium was depleted by BAPTA-AM or thapsigargin, respectively, suggesting that calcium was mobilized from the ER. Inhibitors of G-protein coupled receptors (GPCRs)-mediated signals, including U-73122, a phospholipase C (PLC) inhibitor and xestospongin C, an inositol 1,4,5-triphosphate receptors (IP3R) antagonist, significantly suppressed remimazolam-induced calcium elevation, whereas dantrolene, a ryanodine receptor antagonist, did not influence remimazolam-induced calcium elevation. Meanwhile, live imaging of ER during remimazolam stimulation using ER-tracker showed no morphological changes. These results suggest that high doses of remimazolam increased intracellular calcium concentration in a dose-dependent manner in each cell tested, which was predicted to be caused by calcium mobilization from the ER. In addition, our studies using various inhibitors revealed that this calcium elevation might be mediated by the GPCRs-IP3 pathway. However, further studies are required to identify which type of GPCRs is involved.

Remimazolam: Non-Clinical and Clinical Profile of a New Sedative/Anesthetic Agent

A program to identify novel intravenous sedatives with a short and predictable duration of action was initiated in the late 1990's by Glaxo Wellcome. The program focussed on the identification of ester-based benzodiazepine derivatives that are rapidly broken down by esterases. Remimazolam was identified as one of the lead compounds. The project at Glaxo was shelved for strategic reasons at the late lead optimization stage. Via the GSK ventures initiative, the program was acquired by the small biotechnology company, TheraSci, and, through successive acquisitions, developed as the besylate salt at CeNeS and PAION. The development of remimazolam besylate has been slow by industry standards, primarily because of the resource limitations of these small companies. It has, however, recently been approved for anesthesia in Japan and South Korea, procedural sedation in the United States, China, and Europe, and for compassionate use in intensive care unit sedation in Belgium. A second development program of remimazolam was later initiated in China, using a slightly different salt form, remimazolam tosylate. This salt form of the compound has also recently been approved for procedural sedation in China. Remimazolam has the pharmacological profile of a classical benzodiazepine, such as midazolam, but is differentiated from other intravenous benzodiazepines by its rapid conversion to an inactive metabolite resulting in a short onset/offset profile. It is differentiated from other intravenous hypnotic agents, such as propofol, by its low liability for cardiovascular depression, respiratory depression, and injection pain. The benzodiazepine antagonist flumazenil can reverse the effects of remimazolam in case of adverse events and further shorten recovery times. The aim of this review is to provide an analysis of, and perspective on, published non-clinical and clinical information on 1) the pharmacology, metabolism, pharmacokinetics, and pharmacodynamic profile of remimazolam, 2) the profile of remimazolam compared with established agents, 3) gaps in the current understanding of remimazolam, 4) the compound's discovery and development process and 5) likely future developments in the clinical use of remimazolam.