Stereostructure-based differences in the interactions of cardiotoxic local anesthetics with cholesterol-containing biomimetic membranes

Differences in sensory nerve block between levobupivacaine and bupivacaine at low concentrations in humans and animals

Physiochemical properties of levobupivacaine and bupivacaine are identical, but pharmacokinetic and pharmacodynamics properties differ due to stereoselective interactions at the molecular sites of action. An evaluation of nerve block characteristics is essential for optimal clinical application. This study compared the sensory blocking characteristics of levobupivacaine to bupivacaine in humans and model animals. Levobupivacaine and bupivacaine were compared for sensory block efficacy using a randomized, double-blinded, crossover study design. Eighteen healthy volunteers were randomized to receive levobupivacaine or bupivacaine by subcutaneous injection into the forearm, followed by the other drug 1 week later with injection order counterbalanced across subjects. Tactile detection and mechanical pain thresholds were determined using von Frey hairs and thermal pain threshold using a thermal stimulator. Effects of levobupivacaine and bupivacaine, on the spiking activity of spinal dorsal horn (SDH) neurons evoked by innocuous or noxious stimuli were also compared in anesthetized Sprague-Dawley rats by in vivo extracellular recordings. There were no significant differences in mechanical and thermal pain thresholds following levobupivacaine or bupivacaine injection at 0.025%, 0.0625%, and 0.125%. There was also no significant difference in tactile detection threshold following levobupivacaine or bupivacaine injection at 0.125%. However, tactile detection threshold was significantly higher after administration of bupivacaine at 0.025% and 0.0625% compared to equivalent doses of levobupivacaine. Subcutaneous injection of bupivacaine at 0.05% also induced significantly greater inhibition of SDH neuron spiking activity evoked by innocuous stimuli compared to an equivalent dose of levobupivacaine, while there was no significant difference in suppression of spiking activity evoked by noxious stimuli. Low-dose bupivacaine induces greater suppression tactile sensation than low-dose levobupivacaine. Thus, low-dose levobupivacaine demonstrates relatively greater blocking selectivity for noxious over innocuous stimuli compared to low-dose bupivacaine. Levobupivacaine may be advantageous for applications where pain must be suppressed but non-nociceptive sensations maintained.

Probing the Role of Chirality in Phospholipid Membranes

Nucleotides, amino acids, sugars, and lipids are almost ubiquitously homochiral within individual cells on Earth. While oligonucleotides and proteins exist as one natural chirality throughout the tree of life, two stereoisomers of phospholipids have separately emerged in archaea and bacteria, an evolutionary divergence known as "the lipid divide". Within this review, we focus on the emergence of phospholipid homochirality and compare the stability of synthetic homochiral and heterochiral membranes in vitro. We discuss chemical probes designed to study the stereospecific interactions of lipid membranes in vitro. Overall, we aim to highlight studies that help elucidate the determinants of stereospecific interactions between lipids, peptides, and small molecule ligands. Continued work in understanding the drivers of favorable interactions between chiral molecules and biological membranes will lead to the design of increasingly selective chemical tools for bioorthogonal labeling of lipid membranes and safer membrane-associating pharmaceuticals.

Effect of tetracaine on dynamic reorganization of lipid membranes

To understand the intrinsic influence of a drug on lipid membranes is of critical importance in pharmacological science. Herein, we report fluorescence microscopy analysis of the interaction between the local anesthetic tetracaine (TTC) and planar supported lipid bilayers (SLBs), as model membranes. Our results show that TTC increases lipid chain mobility, destabilizes the SLBs and remarkably induces membrane disruption and solubilization. Upon TTC binding, a local curvature change in the bilayer was observed, which led to the subsequent formation of up to 20-μm-long flexible lipid tubules as well as the formation of micron-size holes. Quantitative analysis revealed that membrane solubilization process can be divided into two distinct different stages as a function of TTC concentration. In the first stage (<800 μM), the bilayer disruption profiles fit well to a Langmuir isotherm, while in the second stage (800 μM-25 mM), TTC solubilizes the membrane in a detergent-like manner. Notably, the onset of membrane solubilization occurred below the critical micelle concentration (cmc) of TTC, indicating a local accumulation of the drug in the membrane. Additionally, cholesterol increases the insertion of TTC into the membrane and thus promotes the solubilization effect of TTC on lipid bilayers. These findings may help to elucidate the possible mechanisms of TTC interaction with lipid membranes, the dose dependent toxicity attributed to local anesthetics, as well as provide valuable information for drug development and modification.

Injectable nanocomposite analgesic delivery system for musculoskeletal pain management

Musculoskeletal pain is a major health issue which results from surgical procedures (i.e. total knee and/or hip replacements and rotator cuff repairs), as well as from non-surgical conditions (i.e. sympathetically-mediated pain syndrome and occipital neuralgia). Local anesthetics, opioids or corticosteroids are currently used for the pain management of musculoskeletal conditions. Even though local anesthetics are highly preferred, the need for multiple administration presents significant disadvantages. Development of unique delivery systems that can deliver local anesthetics at the injection site for prolonged time could significantly enhance the therapeutic efficacy and patient comfort. The goal of the present study is to evaluate the efficacy of an injectable local anesthetic nanocomposite carrier to provide sustained analgesic effect. The nanocomposite carrier was developed by encapsulating ropivacaine, a local anesthetic, in lipid nanocapsules (LNC-Rop), and incorporating the nanocapsules in enzymatically crosslinked glycol chitosan (0.3GC) hydrogels. Cryo Scanning Electron Microscopic (Cryo SEM) images showed the ability to distribute the LNCs within the hydrogel without adversely affecting their morphology. The study demonstrated the feasibility to achieve sustained release of lipophilic molecules from the nanocomposite carrier in vitro and in vivo. A rat chronic constriction injury (CCI) pain model was used to evaluate the efficacy of the nanocomposite carrier using thermal paw withdrawal latency (TWL). The nanocomposite carriers loaded with ropivacaine and dexamethasone showed significant improvement in pain response compared to the control groups for at least 7 days. The study demonstrated the clinical potential of these nanocomposite carriers for post-operative and neuropathic pain.

STATEMENT OF SIGNIFICANCE

Acute or chronic pain associated with musculoskeletal conditions is considered a major health issue, with healthcare costs totaling several billion dollars. The opioid crisis presents a pressing clinical need to develop alternative and effective approaches to treat musculoskeletal pain. The goal of this study was to develop a long-acting injectable anesthetic formulation which can sustain a local anesthetic effect for a prolonged time. This in turn could increase the quality of life and rehabilitation outcome of patients, and decrease opioid consumption. The developed injectable nanocomposite demonstrated the feasibility to achieve prolonged pain relief in a rat chronic constriction injury (CCI) model.

Local anaesthetic pain relief therapy: In vitro and in vivo evaluation of a nanotechnological formulation co-loaded with ropivacaine and dexamethasone

Combination therapy is frequently applied to anesthesia and analgesia for its benefits, which includes prolonged analgesia following peripheral nerve blockade, and reduced side effects. The aim of this study was to develop chitosan (CH) coated poly(ε-caprolactone) (PCL) nanoparticles to co-deliver ropivacaine (RPV) and dexamethasone (DEM) (RPV/DEM CH-PCL NPs) for the prolongation of anesthesia and pain relief. In the present study, RPV/DEM CH-PCL NPs were fabricated. The properties of CH-PCL NPs were evaluated for their particle sizes, zeta potential, drug loading capacity and in vitro drug release profile. In vitro skin permeation and in vivo therapeutic effect in an animal model were further investigated. The results showed that the NPs was around 190nm, with PDI of less than 0.20. The zeta potentials of NPs were about 36mV. In vitro drug release of both RPV and DEM from NPs complied with sustained behaviors. All of the drugs loaded NPs samples studied exhibited no obvious L929 cells cytotoxicity. In vitro skin penetration profiles showed the amount of RPV permeated through the skin from NPs was significantly higher than free RPV. RPV and DEM co-loaded NPs induced remarkably better anesthetic effect than non DEM loaded RPV CH-PCL NPs. The results suggested that adding a small dosage of DEM could improve the anesthesia efficacy of RVP to a large content. The resulting formulation could be applied as a promising anesthesia system for local anesthetics therapy.

A highly stereo-controlled protocol to prepare pipecolic acids based on Heck and cyclohydrocarbonylation reactions

A consecutive series of metal-catalyzed reactions for the preparation of enantiomerically pure piperidine derivatives.

Facile fabrication of polyanhydride/anesthetic nanoparticles with tunable release kinetics

This work illustrates a two-step strategy for the fabrication of polymer/drug nanoparticles. Utilizing solvent/non-solvent precipitation and gaseous basification, composite nanoparticles with 0-100% drug loadings are fabricated. Drug release kinetics are dictated by nanoparticle composition allowing future tuning for therapeutic applications.

Characteristic interactivity of landiolol, an ultra-short-acting highly selective β1-blocker, with biomimetic membranes: Comparisons with β1-selective esmolol and non-selective propranolol and alprenolol

Although β1-blockers have been perioperatively used to reduce the cardiac disorders associated with general anesthesia, little is known about the mechanistic characteristics of ultra-short-acting highly selective β1-blocker landiolol. We studied its membrane-interacting property in comparison with other selective and non-selective β1-blockers. Biomimetic membranes prepared with phospholipids and cholesterol of varying compositions were treated with β1-selective landiolol and esmolol and non-selective propranolol and alprenolol at 0.5-200 μM. The membrane interactivity and the antioxidant activity were determined by measuring fluorescence polarization and by peroxidizing membrane lipids with peroxynitrite, respectively. Non-selective β1-blockers, but not selective ones, intensively acted on 1,2-dipalmitoylphosphatidylcholine (DPPC) liposomal membranes and cardiomyocyte-mimetic membranes to increase the membrane fluidity. Landiolol and its inactive metabolite distinctively decreased the fluidity of DPPC liposomal membranes, suggesting that a membrane-rigidifying effect is attributed to the morpholine moiety in landiolol structure but unlikely to clinically contribute to the β1-blocking effect of landiolol. Propranolol and alprenolol interacted with lipid raft model membranes, whereas neither landiolol nor esmolol. All drugs fluidized mitochondria-mimetic membranes and inhibited the membrane lipid peroxidation with the potency correlating to their membrane interactivity. Landiolol is characterized as a drug devoid of the interactivity with membrane lipid rafts relating to β2-adrenergic receptor blockade. The differentiation between β1-blocking selectivity and non-selectivity is compatible with that between membrane non-interactivity and interactivity. The mitochondrial membrane fluidization by landiolol independent of blocking β1-adrenergic receptors is responsible for the antioxidant cardioprotection common to non-selective and selective β1-blockers.

Interaction of local anesthetics with biomembranes consisting of phospholipids and cholesterol: mechanistic and clinical implications for anesthetic and cardiotoxic effects

Despite a long history in medical and dental application, the molecular mechanism and precise site of action are still arguable for local anesthetics. Their effects are considered to be induced by acting on functional proteins, on membrane lipids, or on both. Local anesthetics primarily interact with sodium channels embedded in cell membranes to reduce the excitability of nerve cells and cardiomyocytes or produce a malfunction of the cardiovascular system. However, the membrane protein-interacting theory cannot explain all of the pharmacological and toxicological features of local anesthetics. The administered drug molecules must diffuse through the lipid barriers of nerve sheaths and penetrate into or across the lipid bilayers of cell membranes to reach the acting site on transmembrane proteins. Amphiphilic local anesthetics interact hydrophobically and electrostatically with lipid bilayers and modify their physicochemical property, with the direct inhibition of membrane functions, and with the resultant alteration of the membrane lipid environments surrounding transmembrane proteins and the subsequent protein conformational change, leading to the inhibition of channel functions. We review recent studies on the interaction of local anesthetics with biomembranes consisting of phospholipids and cholesterol. Understanding the membrane interactivity of local anesthetics would provide novel insights into their anesthetic and cardiotoxic effects.

Pharmacology of local anesthetics used in oral surgery

This article provides a comprehensive review of the pharmacology of local anesthetics as a class, and provides details of the individual drugs available in dental cartridges. Maximum recommended doses of local anesthetics and vasoconstrictors are presented for healthy adult and pediatric patients, and for patients with cardiovascular system impairments. Various complications and reasons for failure of local anesthesia effectiveness are discussed, and current and future trends in local anesthesia are presented to provide an overview of current research in local anesthesia.

Anesthetics interacting with lipid rafts

The exact mechanism by which anesthetics induce cell membrane-mediated modifications is still an open question. Although the fluidization effect of the anesthetic molecules on the cellular membrane is widely recognized, it is not known if anesthetics show any preference for specific membrane domains, namely the lipid rafts. The importance of these membrane micro-domains derives from the fact that they have been associated with cell signaling pathways, as well as with specific drug interactions. The objective of this work is to contribute for the elucidation of this question through the comparison of the anesthetic interactions with membranes of various lipid compositions. Liposomes prepared with an equimolar mixture of POPC, sphingomyelin and cholesterol, were chosen as models for lipid rafts. The interactions of these liposomes with two local anesthetics, tetracaine and lidocaine, and one general anesthetic, propofol, were studied. The effect of cholesterol was investigated by comparing anesthetic interactions with POPC/SM liposomes and POPC/SM/CHOL liposomes. The following experimental techniques were used: quartz crystal microbalance with dissipation, differential scanning calorimetry and phosphorus nuclear magnetic resonance. Although the liposomes investigated by the different techniques are not in the same conditions, it is possible to assemble the information obtained from all experimental techniques employed to reach a general conclusion. Tetracaine interacts more with raftlike domains, lidocaine induces stronger modifications on POPC/SM liposomes and the results for propofol are not fully conclusive but it seems to be the least prone to lipid interactions. The results were compared with those obtained with DMPC-containing liposomes, reported in a previous work.

Intravenous lipid emulsion - rescued at LAST

The accidental overdose of local anaesthetics may prove fatal. The commonly used amide local anaesthetics have varying adverse effects on the myocardium and beyond a certain dose all are capable of causing death. Local anaesthetics are the most frequently used drugs in dentistry and although uncommon, local anaesthetic systemic toxicity (LAST) accounts for a high proportion of mortalities in the dental office, with local anaesthetic-induced cardiac arrest particularly resistant to standard resuscitation methods. Over the last decade there has been convincing evidence of using intravenous lipid emulsions as a rescue in local anaesthetic - cardiotoxicity and anaesthetic organisations over the globe have developed guidelines on the use of this drug. Despite this, however, awareness among practitioners appears to be lacking. All who use local anaesthetics in their practice should have an appreciation of patients at high risk of toxicity, early symptoms and signs of toxicity, preventative measures when using these drugs and the initial management of systemic toxicity with intravenous lipid emulsion. In this review we intend to discuss the pharmacology and pathophysiology of local anaesthetic toxicity, and the rationale for intravenous lipid emulsion therapy.

Lipid emulsion for local anesthetic systemic toxicity

The accidental overdose of local anesthetics may prove fatal. The commonly used amide local anesthetics have varying adverse effects on the myocardium, and beyond a certain dose all are capable of causing death. Local anesthetics are the most frequently used drugs amongst anesthetists and although uncommon, local anaesthetic systemic toxicity accounts for a high proportion of mortality, with local anaesthetic-induced cardiac arrest particularly resistant to standard resuscitation methods. Over the last decade, there has been convincing evidence of intravenous lipid emulsions as a rescue in local anesthetic-cardiotoxicity, and anesthetic organisations, over the globe have developed guidelines on the use of this drug. Despite this, awareness amongst practitioners appears to be lacking. All who use local anesthetics in their practice should have an appreciation of patients at high risk of toxicity, early symptoms and signs of toxicity, preventative measures when using local anesthetics, and the initial management of systemic toxicity with intravenous lipid emulsion. In this paper we intend to discuss the pharmacology and pathophysiology of local anesthetics and toxicity, and the rationale for lipid emulsion therapy.