Neurosteroid modulation of native and recombinant GABAA receptors

1. The pioneering work of Hans Selye over 50 years ago demonstrated that certain steroid metabolites can produce a rapid depression of central nervous system activity. 2. Research during the last 10 years has established that such effects are mediated by a nongenomic and specific interaction of these steroids with the brain's major inhibitory receptor, the GABAA receptor. 3. Here we describe the molecular mechanism of action of such steroids and review attempts to define the steroid binding site on the receptor protein. The therapeutic potential of such neurosteroids is discussed.

Anesthetic effects of a mixture of medetomidine, midazolam and butorphanol in two strains of mice

The combination of ketamine and xylazine is a widely used anesthetic for laboratory animals. However, due to an abuse problem in Japan, ketamine has been specified as a narcotic since 2007. Instead of using ketamine, Kawai et al. reported an injectable formula with an equivalent effect to the mixture of ketamine and xylazine [11]. The mixture of 0.3 mg/kg body weight (b.w.) medetomidine (Med.), 4.0 mg/kg b.w. midazoram (Mid.), and 5.0 mg/kg b.w. butorphanol (But.) produced an anesthetic duration of around 40 min in outbred ICR mice. However, the anesthetic effect of the mixture for inbred mice strains remains unknown. Therefore, we examined anesthetic effects of the mixture of Med., Mid., and But. in the BALB/c and C57BL/6J strains. After intraperitoneal injection into mice, right front paw, left hind paw, and tail pinch reflexes as well as corneal and righting reflexes were observed. Every 5 min, we scored each reflex category as 0 for reaction or 1 for no reaction. As long as the total score was at least 4 out of 5, we considered the mixture as putting a mouse in a surgical anesthetic state. The mixture produced an anesthetic duration of more than 45 min in both strains of mice. These results indicate that the mixture of Med., Mid., and But. can be a useful and effective anesthesia for the BALB/c and C57BL/6J strains of inbred mice as well as outbred ICR mice.

Chiral Alkyl Halides: Underexplored Motifs in Medicine

While alkyl halides are valuable intermediates in synthetic organic chemistry, their use as bioactive motifs in drug discovery and medicinal chemistry is rare in comparison. This is likely attributable to the common misconception that these compounds are merely non-specific alkylators in biological systems. A number of chlorinated compounds in the pharmaceutical and food industries, as well as a growing number of halogenated marine natural products showing unique bioactivity, illustrate the role that chiral alkyl halides can play in drug discovery. Through a series of case studies, we demonstrate in this review that these motifs can indeed be stable under physiological conditions, and that halogenation can enhance bioactivity through both steric and electronic effects. Our hope is that, by placing such compounds in the minds of the chemical community, they may gain more traction in drug discovery and inspire more synthetic chemists to develop methods for selective halogenation.

Sevoflurane

Sevoflurane has been available for clinical practice for about 20 years. Nowadays, its pharmacodynamic and pharmacokinetic properties together with its absence of major adverse side effects on the different organ systems have made this drug accepted worldwide as a safe and reliable anesthetic agent for clinical practice in various settings.

Mechanisms of barbiturate inhibition of acetylcholine receptor channels

We used patch clamp techniques to study the inhibitory effects of pentobarbital and barbital on nicotinic acetylcholine receptor channels from BC3H-1 cells. Single channel recording from outside-out patches reveals that both drugs cause acetylcholine-activated channel events to occur in bursts. The mean duration of gaps within bursts in 2 ms for 0.1 mM pentobarbital and 0.05 ms for 1 mM barbital. In addition, 1 mM barbital reduces the apparent single channel current by 15%. Both barbiturates decrease the duration of openings within a burst but have only a small effect on the burst duration. Macroscopic currents were activated by rapid perfusion of 300 microM acetylcholine to outside-out patches. The concentration dependence of peak current inhibition was fit with a Hill function; for pentobarbital, Ki = 32 microM, n = 1.09; for barbital, Ki = 1900 microM, n = 1.24. Inhibition is voltage independent. The kinetics of inhibition by pentobarbital are at least 30 times faster than inhibition by barbital (3 ms vs. < 0.1 ms at the Ki). Pentobarbital binds > or = 10-fold more tightly to open channels than to closed channels; we could not determine whether the binding of barbital is state dependent. Experiments performed with both barbiturates reveal that they do not compete for a single binding site on the acetylcholine receptor channel protein, but the binding of one barbiturate destabilizes the binding of the other. These results support a kinetic model in which barbiturates bind to both open and closed states of the AChR and block the flow of ions through the channel. An additional, lower-affinity binding site for pentobarbital may explain the effects seen at > 100 microM pentobarbital.

Guidelines for sedation in gastroenterological endoscopy

Recently, the need for sedation in gastrointestinal endoscopy has been increasing. However, the National Health Insurance Drug Price list in Japan does not include any drug specifically used for the sedation. Although benzodiazepines are the main medication, their use in cases of gastrointestinal endoscopy has not been approved. This has led the Japan Gastrointestinal Endoscopy Society to develop the first set of guidelines for sedation in gastrointestinal endoscopy on the basis of evidence-based medicine in collaboration with the Japanese Society for Anesthesiologists. The present guidelines comprise 14 statements, five of which were judged to be valid on the highest evidence level and three on the second highest level. The guidelines are not intended to strongly recommend the use of sedation for gastrointestinal endoscopy, but rather to indicate the policy as to the choice of appropriate procedures when such sedation is deemed necessary. In clinical practice, the final decision as to the use of sedation should be made by physicians considering patient willingness and physical condition.

The influence of the membrane on neurosteroid actions at GABA(A) receptors

Modern views of anesthetic neurosteroid interaction with the GABA(A) receptor conceptualize steroid ligands interacting with a protein binding site on the receptor. It has generally been assumed that the steroid interaction/binding site is contained in an extracellular domain of the receptor, and that steroid interactions are of high potency, evidenced by the low aqueous ligand concentrations required to achieve potentiation of channel function. We have been considering implications of the observations that steroids are quite lipophilic and that recently identified putative steroid binding sites are in transmembrane domains of the receptor. Accordingly, we expect that both the effective plasma membrane steroid concentration and steroid pharmacophore properties will contribute to steady-state potency and to the lifetime of steroid actions following removal of free aqueous steroid. Here we review our recent studies that address the evidence that membrane partitioning and intracellular accumulation are non-specific contributors to the effects of anesthetic steroids at GABA(A) receptors. We compare and contrast the profile of anesthetic steroids with that of sulfated steroids that negatively regulate GABA(A) receptor function. These studies give rise to the view that the inherent affinity of anesthetic steroid for GABA(A) receptors is very low; low effective aqueous concentrations are accounted for by lipid partitioning. This yields a very different picture of the interaction of neurosteroids with the GABA(A) receptor than that of steroid interactions with classical intracellular steroid receptors, which exhibit inherently high affinity. These considerations have practical implications for actions of endogenous neurosteroids. Lipophilicity will tend to promote autocrine actions of neurosteroids at GABA(A) receptors within cells that synthesize neurosteroids, and lipophilic retention will limit intercellular diffusion from the source of steroid synthesis. Lipophilicity and steroid access to the receptor binding sites also must be considerations in drug design if drugs are to effectively reach the target GABA(A) receptor site.

Cerebral Glutamate Regulation and Receptor Changes in Perioperative Neuroinflammation and Cognitive Dysfunction

Glutamate is the major excitatory neurotransmitter in the central nervous system and is intricately linked to learning and memory. Its activity depends on the expression of AMPA and NMDA receptors and excitatory amino transporters on neurons and glial cells. Glutamate transporters prevent the excess accumulation of glutamate in synapses, which can lead to aberrant synaptic signaling, excitotoxicity, or cell death. Neuroinflammation can occur acutely after surgical trauma and contributes to the development of perioperative neurocognitive disorders, which are characterized by impairment in multiple cognitive domains. In this review, we aim to examine how glutamate handling and glutamatergic function are affected by neuroinflammation and their contribution to cognitive impairment. We will first summarize the current data regarding glutamate in neurotransmission, its receptors, and their regulation and trafficking. We will then examine the impact of inflammation on glutamate handling and neurotransmission, focusing on changes in glial cells and the effect of cytokines. Finally, we will discuss these changes in the context of perioperative neuroinflammation and the implications they have for perioperative neurocognitive disorders.

Spontaneous activity in the piriform cortex extends the dynamic range of cortical odor coding

Neurons in the neocortex exhibit spontaneous spiking activity in the absence of external stimuli, but the origin and functions of this activity remain uncertain. Here, we show that spontaneous spiking is also prominent in a sensory paleocortex, the primary olfactory (piriform) cortex of mice. In the absence of applied odors, piriform neurons exhibit spontaneous firing at mean rates that vary systematically among neuronal classes. This activity requires the participation of NMDA receptors and is entirely driven by bottom-up spontaneous input from the olfactory bulb. Odor stimulation produces two types of spatially dispersed, odor-distinctive patterns of responses in piriform cortex layer 2 principal cells: Approximately 15% of cells are excited by odor, and another approximately 15% have their spontaneous activity suppressed. Our results show that, by allowing odor-evoked suppression as well as excitation, the responsiveness of piriform neurons is at least twofold less sparse than currently believed. Hence, by enabling bidirectional changes in spiking around an elevated baseline, spontaneous activity in the piriform cortex extends the dynamic range of odor representation and enriches the coding space for the representation of complex olfactory stimuli.

Anesthetic-Related Neurotoxicity and Neuroimaging in Children: A Call for Conversation

Each year millions of young children undergo procedures requiring sedation or general anesthesia. An increasing proportion of the anesthetics used are provided to optimize diagnostic imaging studies such as magnetic resonance imaging. Concern regarding the neurotoxicity of sedatives and anesthetics has prompted the US Food and Drug Administration to change labeling of anesthetics and sedative agents warning against repeated or prolonged exposure in young children. This review aims to summarize the risk of anesthesia in children with an emphasis on anesthetic-related neurotoxicity, acknowledge the value of pediatric neuroimaging, and address this call for conversation.

A Novel Bifunctional Alkylphenol Anesthetic Allows Characterization of γ-Aminobutyric Acid, Type A (GABAA), Receptor Subunit Binding Selectivity in Synaptosomes

Propofol, an intravenous anesthetic, is a positive modulator of the GABAA receptor, but the mechanistic details, including the relevant binding sites and alternative targets, remain disputed. Here we undertook an in-depth study of alkylphenol-based anesthetic binding to synaptic membranes. We designed, synthesized, and characterized a chemically active alkylphenol anesthetic (2-((prop-2-yn-1-yloxy)methyl)-5-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenol, AziPm-click (1)), for affinity-based protein profiling (ABPP) of propofol-binding proteins in their native state within mouse synaptosomes. The ABPP strategy captured ∼4% of the synaptosomal proteome, including the unbiased capture of five α or β GABAA receptor subunits. Lack of γ2 subunit capture was not due to low abundance. Consistent with this, independent molecular dynamics simulations with alchemical free energy perturbation calculations predicted selective propofol binding to interfacial sites, with higher affinities for α/β than γ-containing interfaces. The simulations indicated hydrogen bonding is a key component leading to propofol-selective binding within GABAA receptor subunit interfaces, with stable hydrogen bonds observed between propofol and α/β cavity residues but not γ cavity residues. We confirmed this by introducing a hydrogen bond-null propofol analogue as a protecting ligand for targeted-ABPP and observed a lack of GABAA receptor subunit protection. This investigation demonstrates striking interfacial GABAA receptor subunit selectivity in the native milieu, suggesting that asymmetric occupancy of heteropentameric ion channels by alkylphenol-based anesthetics is sufficient to induce modulation of activity.

Structure-Dependent Activity of Natural GABA(A) Receptor Modulators

GABA(A) receptors are ligand-gated ion channels consisting of five subunits from eight subfamilies, each assembled in four hydrophobic transmembrane domains. This pentameric structure not only allows different receptor binding sites, but also various types of ligands, such as orthosteric agonists and antagonists, positive and negative allosteric modulators, as well as second-order modulators and non-competitive channel blockers. A fact, that is also displayed by the variety of chemical structures found for both, synthetic as well as nature-derived GABA(A)-receptor modulators. This review covers the literature for natural GABA(A)-receptor modulators until the end of 2017 and discusses their structure-activity relationship.

Endoplasmic reticulum stress mediates distinct impacts of sevoflurane on different subfields of immature hippocampus

Sevoflurane, a typical inhaled anesthetic, is widely used in patients of all ages during surgery. The negative effects, such as inducing cell death and damaging spatial memory, of sevoflurane on neurodevelopment have raised increasing concerns in recent years. However, the molecular mechanism remains unclear. This study focused on the crucial role of endoplasmic reticulum (ER) stress in sevoflurane-induced hippocampal injury. Three-week-old rats were exposed to sevoflurane or control air for 5 h with or without ER stress inhibitor (4-phenylbutyric acid, 4-PBA) injection. The hippocampus was harvested to measure the ER stress sensors by western immunoblotting. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling staining was used to detect cell apoptosis and electrophysiology was used to measure the intrinsic excitability of neurons in hippocampus. We measured learning and memory ability by Morris water maze tests 5 weeks after sevoflurane exposure. Interestingly, persistent sevoflurane exposure significantly increased the levels of ER stress sensors in hippocampus. But it resulted in different effects in CA1 and dentate gyrus. Greatly increased caspase-12-mediated apoptotic cells, which were proved to be the neural stem cells, were detected in the dentate gyrus. Meanwhile, CA1 pyramidal neurons exhibited significantly reduced intrinsic excitability. Furthermore, the administration of ER stress inhibitor attenuated the above mentioned detrimental effects evidently and prevented the following relevant learning and memory deficits. In conclusion, sevoflurane-mediated ER stress performs distinct effects on the different subfields of the immature hippocampus and inhibiting ER stress during sevoflurane anesthesia will be a potential method to prevent the following learning and memory deficits in adulthood.

Isoflurane, ketamine-xylazine, and urethane markedly alter breathing even at subtherapeutic doses

Anesthetics are widely used for animal research on respiratory control in vivo, but their effect on breathing and CO₂ chemoreception has not been well characterized in mice, a species now often used for these studies. We previously demonstrated that 1% isoflurane markedly reduces the hypercapnic ventilatory response (HCVR) in adult mice in vivo and masks serotonin [5-hydroxytryptamine (5-HT)] neuron chemosensitivity in vitro. Here we investigated effects of 0.5% isoflurane on breathing in adult mice and also found a large reduction in the HCVR even at this subanesthetic concentration. We then tested the effects on breathing of ketamine-xylazine and urethane, anesthetics widely used in research on breathing. We found that these agents altered baseline breathing and blunted the HCVR at doses within the range typically used experimentally. At lower doses ventilation was decreased, but mice appropriately matched their ventilation to metabolic demands due to a parallel decrease in O₂ consumption. Neither ketamine nor urethane decreased chemosensitivity of 5-HT neurons. These results indicate that baseline breathing and/or CO₂ chemoreception in mice are decreased by anesthetics widely viewed as not affecting respiratory control, and even at subtherapeutic doses. These effects of anesthetics on breathing may alter the interpretation of studies of respiratory physiology in vivo.NEW & NOTEWORTHY Anesthetics are frequently used in animal research, but their effects on physiological functions in mice have not been well defined. Here we investigated the effects of commonly used anesthetics on breathing in mice. We found that all tested anesthetics significantly reduced the hypercapnic ventilatory response (HCVR), even at subtherapeutic doses. In addition, ketamine-xylazine and urethane anesthesia altered baseline breathing. These data indicate that breathing and the HCVR in mice are highly sensitive to anesthetic modulation.

Quality of recovery in patients undergoing endoscopic sinus surgery after general anesthesia: total intravenous anesthesia vs desflurane anesthesia

BACKGROUND

For sinus surgery, some centers favor total intravenous anesthesia (TIVA) over inhalation anesthesia. However, whether TIVA affects the patient's perceived quality of recovery remains unclear. This study used the Quality of Recovery-40 questionnaire (QoR-40) to compare patient recovery between surgical patients who received TIVA and those who received desflurane (DES) anesthesia.

METHODS

Eighty patients (20 to 65 years old) undergoing endoscopic sinus surgery were prospectively enrolled and randomized to either the TIVA (propofol and remifentanil infusion) or DES (desflurane inhalation and remifentanil infusion) group. The QoR-40 was administered before surgery, at 6 hours after surgery, and on postoperative day 1 (POD1). Incidence of nausea and vomiting, remifentanil consumption, blood loss, and pain treatment were recorded. The influence of lesion extent (indexed as Lund-Mackay [LM] score) on recovery quality was also assessed.

RESULTS

Forty patients were randomized into the TIVA group, and 40 patients were randomized into the DES group. The QoR-40 score at 6 hours after surgery was significantly higher in the TIVA group compared with the DES group (188.2 vs 182.6, respectively; p = 0.049), indicating a better quality of recovery in the TIVA group. TIVA resulted in less blood loss (p < 0.0001). A high LM score (≥12) was associated with lower QoR-40 scores at 6 hours after surgery (180.2 vs 187.2, p = 0.028) and on POD1 (181.5 vs 190.3, p = 0.003).

CONCLUSION

This study shows that the quality of recovery for endoscopic sinus surgery patients was better with TIVA than with desflurane anesthesia. A high LM score was related to poorer recovery quality.

Diaphragmatic pacing stimulation in spinal cord injury: anesthetic and perioperative management

OBJECTIVE

The standard therapy for patients with high-level spinal cord injury is long-term mechanical ventilation through a tracheostomy. However, in some cases, this approach results in death or disability. The aim of this study is to highlight the anesthetics and perioperative aspects of patients undergoing insertion of a diaphragmatic pacemaker.

METHODS

Five patients with quadriplegia following high cervical traumatic spinal cord injury and ventilator-dependent chronic respiratory failure were implanted with a laparoscopic diaphragmatic pacemaker after preoperative assessments of their phrenic nerve function and diaphragm contractility through transcutaneous nerve stimulation. ClinicalTrials.gov: NCT01385384.

RESULTS

The diaphragmatic pacemaker placement was successful in all of the patients. Two patients presented with capnothorax during the perioperative period, which resolved without consequences. After six months, three patients achieved continuous use of the diaphragm pacing system, and one patient could be removed from mechanical ventilation for more than 4 hours per day.

CONCLUSIONS

The implantation of a diaphragmatic phrenic system is a new and safe technique with potential to improve the quality of life of patients who are dependent on mechanical ventilation because of spinal cord injuries. Appropriate indication and adequate perioperative care are fundamental to achieving better results.

General Anesthetic Binding Sites in Human α4β3δ γ-Aminobutyric Acid Type A Receptors (GABAARs)

Extrasynaptic γ-aminobutyric acid type A receptors (GABAARs),which contribute generalized inhibitory tone to the mammalian brain, are major targets for general anesthetics. To identify anesthetic binding sites in an extrasynaptic GABAAR, we photolabeled human α4β3δ GABAARs purified in detergent with [3H]azietomidate and a barbiturate, [3H]R-mTFD-MPAB, photoreactive anesthetics that bind with high selectivity to distinct but homologous intersubunit binding sites in the transmembrane domain of synaptic α1β3γ2 GABAARs. Based upon 3H incorporation into receptor subunits resolved by SDS-PAGE, there was etomidate-inhibitable labeling by [3H]azietomidate in the α4 and β3 subunits and barbiturate-inhibitable labeling by [3H]R-mTFD-MPAB in the β3 subunit. These sites did not bind the anesthetic steroid alphaxalone, which enhanced photolabeling, or DS-2, a δ subunit-selective positive allosteric modulator, which neither enhanced nor inhibited photolabeling. The amino acids labeled by [3H]azietomidate or [3H]R-mTFD-MPAB were identified by N-terminal sequencing of fragments isolated by HPLC fractionation of enzymatically digested subunits. No evidence was found for a δ subunit contribution to an anesthetic binding site. [3H]azietomidate photolabeling of β3Met-286 in βM3 and α4Met-269 in αM1 that was inhibited by etomidate but not by R-mTFD-MPAB established that etomidate binds to a site at the β3+-α4- interface equivalent to its site in α1β3γ2 GABAARs. [3H]Azietomidate and [3H]R-mTFD-MPAB photolabeling of β3Met-227 in βM1 established that these anesthetics also bind to a homologous site, most likely at the β3+-β3- interface, which suggests a subunit arrangement of β3α4β3δβ3.

Protective Nature of Platelet-Rich Plasma Against Chondrocyte Death When Combined With Corticosteroids or Local Anesthetics

BACKGROUND

The use of corticosteroids and local anesthetics to treat osteoarthritis has established benefits, including relief of pain and increased range of motion, but may also have the potential to lead to tissue atrophy or degeneration, specifically on chondrocytes. There is growing evidence that platelet-rich plasma (PRP) has anti-inflammatory characteristics that can limit the cytotoxic effects of corticosteroids and local anesthetics. Hypothesis/Purpose: The purpose of this study was to determine the effects of PRP in chondrocyte cultures when combined with corticosteroids or local anesthetics. The hypothesis of this study was that PRP would (1) dampen the negative effects on chondrocyte viability and (2) improve chondrocyte proliferation seen with corticosteroid or local anesthetic treatment alone.

STUDY DESIGN

Controlled laboratory study.

METHODS

Peripheral blood was obtained from 8 healthy participants, followed by centrifugation to obtain PRP. Human chondrocytes were treated with PRP alone or in combination with corticosteroids or local anesthetics. Saline (concentration of 0.9%) served as the control. Luminescence and radioactive thymidine assays were performed to examine chondrocyte viability and proliferation, respectively. Cell exposures of 0, 5, 10, and 30 minutes were used for viability and 120 hours for proliferation.

RESULTS

The presence of PRP significantly limited the negative effect on chondrocyte viability at tested time points for the examined corticosteroids and local anesthetics ( P < .05). PRP in addition to corticosteroids and local anesthetics significantly improved chondrocyte proliferation ( P < .05).

CONCLUSION

The addition of PRP can significantly reduce the cytotoxic effects of corticosteroids and/or local anesthetics applied to chondrocytes. PRP can improve the proliferation of chondrocytes compared with corticosteroids or local anesthetics alone.

CLINICAL RELEVANCE

With the use of corticosteroids and local anesthetics for temporary symptomatic relief and improvement of function to treat the chronic progressive nature of osteoarthritis, long-term negative effects of these agents can be limited with the parallel use of PRP.

Safety of Repeated-Dose Intratympanic Injections with AM-101 in Acute Inner Ear Tinnitus

Objective

To evaluate the safety and tolerability of repeated intratympanic administration of the gel-formulated NMDA receptor antagonist AM-101 in acute patients with inner ear tinnitus.

Study Design

Prospective, double-blind, randomized, placebo-controlled study.

Setting

Sixty-nine secondary and tertiary sites in North America, Europe, and Asia.

Subjects and Methods

In total, 343 subjects with persistent acute tinnitus after traumatic cochlear injury or otitis media were randomized to receive 3 intratympanic doses of either AM-101 0.87 mg/mL or placebo over 3 to 5 days. They were followed for 84 days. The primary safety end point was the incidence of a clinically meaningful hearing deterioration from baseline to study day 35. Further safety assessments included tympanic membrane closure rates, analysis of adverse events, hematology, blood chemistry, and vital signs. In addition, data were collected on applied anesthetics and injection techniques.

Results

The treatment was well tolerated, with no intervention-related serious adverse events. The incidence of clinically meaningful hearing deterioration was low, comparable between treatment groups (P = .82 for the primary safety end point) and not different between treated and untreated ears in unilaterally treated subjects. The rate of treatment and procedure-related adverse events was similar among treatment groups. The tympanic membrane was closed in 92% of subjects within 1 week and in all subjects by study day 84. Blood values and vital signs were inconspicuous.

Conclusion

Repeated intratympanic injections of AM-101 over a 3- to 5-day period appear to be safe and well tolerated, demonstrating the ability to potentially use this delivery approach over longer time periods.

A membrane-embedded pathway delivers general anesthetics to two interacting binding sites in the Gloeobacter violaceus ion channel

General anesthetics exert their effects on the central nervous system by acting on ion channels, most notably pentameric ligand-gated ion channels. Although numerous studies have focused on pentameric ligand-gated ion channels, the details of anesthetic binding and channel modulation are still debated. A better understanding of the anesthetic mechanism of action is necessary for the development of safer and more efficacious drugs. Herein, we present a computational study identifying two anesthetic binding sites in the transmembrane domain of the Gloeobacter violaceus ligand-gated ion channel (GLIC) channel, characterize the putative binding pathway, and observe structural changes associated with channel function. Molecular simulations of desflurane reveal a binding pathway to GLIC via a membrane-embedded tunnel using an intrasubunit protein lumen as the conduit, an observation that explains the Meyer-Overton hypothesis, or why the lipophilicity of an anesthetic and its potency are generally proportional. Moreover, employing high concentrations of ligand led to the identification of a second transmembrane site (TM2) that inhibits dissociation of anesthetic from the TM1 site and is consistent with the high concentrations of anesthetics required to achieve clinical effects. Finally, asymmetric binding patterns of anesthetic to the channel were found to promote an iris-like conformational change that constricts and dehydrates the ion pore, creating a 13.5 kcal/mol barrier to ion translocation. Together with previous studies, the simulations presented herein demonstrate a novel anesthetic binding site in GLIC that is accessed through a membrane-embedded tunnel and interacts with a previously known site, resulting in conformational changes that produce a non-conductive state of the channel.

Parahydrogen-Induced Polarization of Diethyl Ether Anesthetic

The growing interest in magnetic resonance imaging (MRI) for assessing regional lung function relies on the use of nuclear spin hyperpolarized gas as a contrast agent. The long gas-phase lifetimes of hyperpolarized 129 Xe make this inhalable contrast agent acceptable for clinical research today despite limitations such as high cost, low throughput of production and challenges of 129 Xe imaging on clinical MRI scanners, which are normally equipped with proton detection only. We report on low-cost and high-throughput preparation of proton-hyperpolarized diethyl ether, which can be potentially employed for pulmonary imaging with a nontoxic, simple, and sensitive overall strategy using proton detection commonly available on all clinical MRI scanners. Diethyl ether is hyperpolarized by pairwise parahydrogen addition to vinyl ethyl ether and characterized by 1 H NMR spectroscopy. Proton polarization levels exceeding 8 % are achieved at near complete chemical conversion within seconds, causing the activation of radio amplification by stimulated emission radiation (RASER) throughout detection. Although gas-phase T1 relaxation of hyperpolarized diethyl ether (at partial pressure of 0.5 bar) is very efficient, with T1 of ca. 1.2 second, we demonstrate that, at low magnetic fields, the use of long-lived singlet states created via pairwise parahydrogen addition extends the relaxation decay by approximately threefold, paving the way to bioimaging applications and beyond.

Novel Findings of Anti-cancer Property of Propofol

BACKGROUND

Propofol, a widely used intravenous anesthetic agent, is traditionally applied for sedation and general anesthesia. Explanation: Recent attention has been drawn to explore the effect and mechanisms of propofol against cancer progression in vitro and in vivo. Specifically, the proliferation-inhibiting and apoptosis-inducing properties of propofol in cancer have been studied. However, the underlying mechanisms remain unclear.

CONCLUSION

This review focused on the findings within the past ten years and aimed to provide a general overview of propofol's malignance-modulating properties and the potential molecular mechanisms.

One-Pot Synthesis of High-Flux b-Oriented MFI Zeolite Membranes for Xe Recovery

We demonstrate that b-oriented MFI (Mobil Five) zeolite membranes can be manufactured by in situ crystallization using an intermediate amorphous SiO₂ layer. The improved in-plane growth by using a zeolite growth modifier leads to fusion of independent crystals and eliminates boundary gaps, giving good selectivity in the separation of CO₂/Xe mixtures. The fast diffusion of CO₂ dominates the overall membrane selectivity toward the CO₂/Xe mixture. Because of the straight and short [010] channels, the obtained CO₂ permeation fluxes are several orders of magnitude higher than those of carbon molecular sieving membranes and polymeric membranes, opening opportunities for Xe recovery from waste anesthetic gas.

Safety, efficacy, and patient acceptability of lidocaine hydrochloride ophthalmic gel as a topical ocular anesthetic for use in ophthalmic procedures

Purpose:

To review the current literature on safety, efficacy, and measures of surgeon and patient satisfaction with lidocaine hydrochloride gel as a tool for ocular anesthesia.

Methods:

Pubmed search using keywords “lidocaine gel,” “ophthalmic,” and “surgery” and compiling cross-references. Twenty-six total references were reviewed, including 15 prospective randomized controlled trials (RCTs, total N = 933, average N = 62), 6 nonrandomized prospective studies (total N = 234, average N = 39), 2 animal studies, 1 microbiologic study, and 2 letters to the editor.

Results:

The RCTs and nonrandomized prospective studies evaluated a number of measures including timing of onset of anesthesia, duration of anesthesia, intraoperative and postoperative pain, need for additional anesthetic applications, intracameral lidocaine levels, and adverse effects. Control groups received topical drops, subconjunctival anesthetic, retrobulbar anesthetic, or sham gel. Lidocaine gel was shown to be at least as effective for pain control as alternative therapies in all studies, with longer duration of action than topical drops. Patient and surgeon satisfaction were high, and adverse effects were rare and comparable to those for anesthetic drop formulations. Surgical settings included cataract, pterygium, trabeculectomy, strabismus, intravitreal injection, vitrectomy, and penetrating keratoplasty.

Conclusions:

Lidocaine gel is a safe, effective, and potentially underutilized tool for ophthalmic surgery.

Effect of Radiation on Sucrose Detection Thresholds of Mice

Radiotherapy is one of the most common treatments for head and neck cancers, with an almost obligate side effect of altered taste (Conger AD. 1973. Loss and recovery of taste acuity in patients irradiated to the oral cavity. Radiat Res. 53:338-347.). In mice, targeted irradiation of the head and neck causes transient repression of proliferation of basal epithelial cells responsible for taste cell replacement, leading to a temporary depletion of taste sensory cells within taste buds, including Type II taste cells involved in detection of sweet stimuli (Nguyen HM, Reyland ME, Barlow LA. 2012. Mechanisms of taste bud cell loss after head and neck irradiation. J Neurosci. 32:3474-3484.). These findings suggest that irradiation may elevate sucrose detection thresholds, peaking at 7 days postirradiation when loss of Type II cells is greatest. To test this hypothesis, sucrose detection thresholds (concentration detected in 50% of presentations) were measured in mice for 15 days after treatment of: 1) irradiation while anesthetized, 2) anesthetic alone, or 3) saline. Mice were trained to distinguish water from several concentrations of sucrose. Mice were irradiated with one 8 Gy dose (RADSOURCE-2000 X-ray Irradiator) to the nose and mouth while under 2,2,2-tribromethanol anesthesia (Avertin). Unexpectedly, mice given anesthesia showed a small elevation in sucrose thresholds compared to saline-injected mice, but irradiated mice show significantly elevated sucrose thresholds compared to either control group, an effect that peaked at 6-8 days postirradiation. The timing of loss and recovery of sucrose sensitivity generally coincides with the reported maximal reduction and recovery of Type II taste cells (Nguyen HM, Reyland ME, Barlow LA. 2012. Mechanisms of taste bud cell loss after head and neck irradiation. J Neurosci. 32:3474-3484.). Thus, even a single dose of irradiation can significantly alter detection of carbohydrates, an important consideration for patients undergoing radiotherapy.