Site of action of the general anesthetic propofol in muscarinic M1 receptor-mediated signal transduction

Dendritic spine remodeling and plasticity under general anesthesia

Ever since its first use in surgery, general anesthesia has been regarded as a medical miracle enabling countless life-saving diagnostic and therapeutic interventions without pain sensation and traumatic memories. Despite several decades of research, there is a lack of understanding of how general anesthetics induce a reversible coma-like state. Emerging evidence suggests that even brief exposure to general anesthesia may have a lasting impact on mature and especially developing brains. Commonly used anesthetics have been shown to destabilize dendritic spines and induce an enhanced plasticity state, with effects on cognition, motor functions, mood, and social behavior. Herein, we review the effects of the most widely used general anesthetics on dendritic spine dynamics and discuss functional and molecular correlates with action mechanisms. We consider the impact of neurodevelopment, anatomical location of neurons, and their neurochemical profile on neuroplasticity induction, and review the putative signaling pathways. It emerges that in addition to possible adverse effects, the stimulation of synaptic remodeling with the formation of new connections by general anesthetics may present tremendous opportunities for translational research and neurorehabilitation.

Intravenous Anesthetic Protects Hepatocyte from Reactive Oxygen Species-Induced Cellular Apoptosis during Liver Transplantation In Vivo

Background

Liver transplantation leads to liver ischemia/reperfusion (I/R) injury, resulting in early graft dysfunction and failure. Exacerbations of oxidative stress and inflammatory response are key processes in the development of liver I/R injury. Intravenous anesthetic propofol potent effects on free radical scavenging and protects livers against I/R injury. However, the role and mechanism of propofol-mediated hepatic protection in liver transplantation is poorly understood. The aim of this study was to evaluate the role of propofol postconditioning in the liver I/R injury after liver transplantation.

Methods

Forty-eight rats were randomly divided into six groups: rats receiving either sham operation or orthotopic autologous liver transplantation (OALT) in the absence or presence of propofol (high dose and low dose) postconditioning or intralipid control or VAS2870 (Nox2 special inhibitor). Eight hours after OALT or sham operation, parameters of organ injury, oxidative stress, inflammation, and NADPH-associated proteins were assessed.

Results

After OALT, severe liver pathological injury was observed that was associated with increases of serum AST and ALT, which were attenuated by propofol postconditioning. In addition, especially high dose of propofol postconditioning reduced TNF-α, IL-1β, IL-6, TLR4, and NF-κB inflammatory pathway, accompanied with decrease of neutrophil elastase activity, MPO activity, 8-isoprotane, p47^phox and gp91^phox protein expressions, and increase of SOD activity. Inhibition of Nox2 by VAS2870 conferred similar protective effects in liver transplantation.

Conclusion

Liver transplantation leads to severe inflammation and oxidative stress with NADPH oxidase activation. Propofol postconditioning reduces liver I/R injury after liver transplantation partly via inhibiting NADPH oxidase Nox2 and the subsequent inflammation and oxidative stress.

Propofol inhibits carbachol-induced chloride secretion by directly targeting the basolateral K+ channel in rat ileum epithelium

BACKGROUND

Propofol is a widely used intravenous general anesthetic. Acetylcholine (ACh) is critical in controlling epithelial ion transport. This study was to investigate the effects of propofol on ACh-evoked secretion in rat ileum epithelium.

METHODS

The Ussing chamber technique was used to investigate the effects of propofol on carbachol (CCh)-evoked short-circuit currents (Isc).

KEY RESULTS

Propofol (10^-2 -10^-6  mol/L) attenuated CCh-evoked Isc of rat ileum mucosa in a dose-dependent manner. The inhibitory effect of propofol was only evident after application to the serosal side. Pretreatment with tetrodotoxin (TTX, 0.3 μmol/L, n=5) had no effect on propofol-induced inhibitory effect, whereas serosal application of K⁺ channel inhibitor, glibenclamide, but not, an ATP-sensitive K⁺ channel inhibitor, largely reduced the inhibitory effect of propofol. In addition, pretreatment with either hexamethonium bromide (HB, nicotinic nACh receptor antagonist) or Cl^- channel blockers niflumic acid and cystic fibrosis transmembrane conductance regulator (inh)-172 did not produce any effect on the propofol-induced inhibitory effect.

CONCLUSIONS & INFERENCES

Propofol inhibits CCh-induced intestinal secretion by directly targeting basolateral K⁺ channels.

Cellular and neurochemical basis of sleep stages in the thalamocortical network

The link between the combined action of neuromodulators in the brain and global brain states remains a mystery. In this study, using biophysically realistic models of the thalamocortical network, we identified the critical intrinsic and synaptic mechanisms, associated with the putative action of acetylcholine (ACh), GABA and monoamines, which lead to transitions between primary brain vigilance states (waking, non-rapid eye movement sleep [NREM] and REM sleep) within an ultradian cycle. Using ECoG recordings from humans and LFP recordings from cats and mice, we found that during NREM sleep the power of spindle and delta oscillations is negatively correlated in humans and positively correlated in animal recordings. We explained this discrepancy by the differences in the relative level of ACh. Overall, our study revealed the critical intrinsic and synaptic mechanisms through which different neuromodulators acting in combination result in characteristic brain EEG rhythms and transitions between sleep stages.

Comparison of the type and severity of early attentional network decline after total intravenous or epidural anesthesia in middle-aged women after gynecological surgery

Compared with regional anesthesia, general anesthesia may increase the risk of postoperative cognitive decline. This study aimed to investigate the type and severity of attentional network decline and the recovery of attentional networks in middle-aged women after gynecological surgery. A total of 140 consenting women undergoing elective gynecological surgery were enrolled in the study. Patients were assigned randomly to receive either total intravenous anesthesia or epidural anesthesia. To determine the efficacy of the attentional networks, patients were examined for alerting, orienting, and executive networks on the preoperative day and on the first and fifth postoperative days using the attentional network test. Significant differences were observed in the effect scores of the three attentional networks at all time points. These effect scores differed significantly between groups and between 1 and 5 days postoperation (DPO). Participants showed significantly lower effect scores for the alerting and orienting network tasks and had more difficulties in resolving conflict at 1 DPO compared with the baseline. On comparing effect scores between baseline and 5 DPO, no significant differences on the alerting and orienting network tasks were observed in the epidural anesthesia group, a significant difference on the orienting network task was observed in the general anesthesia group, and significant differences on the executive control network were observed in both the groups. Compared with epidural anesthesia, total intravenous anesthesia is more likely to impair and delay the recovery of attentional networks in middle-aged women undergoing elective hysterectomy. The executive control function showed marked damage and there were difficulties in recovery from either type of anesthesia.

Effects of acetylcholinesterase inhibition on quality of recovery from isoflurane-induced anesthesia in horses

OBJECTIVE

To compare effects of 2 acetylcholinesterase inhibitors on recovery quality of horses anesthetized with isoflurane.

ANIMALS

6 horses in phase 1, 7 horses in phase 2A, and 14 horses in phase 2B.

PROCEDURES

The study comprised 3 phases (2 randomized, blinded crossover phases in horses undergoing orthopedic procedures and 1 prospective dose-determining phase). In phase 1, horses were anesthetized with isoflurane and received neostigmine or saline (0.9% NaCl) solution prior to anesthetic recovery. Phase 2A was a physostigmine dose-determining phase. In phase 2B, horses were anesthetized with isoflurane and received neostigmine or physostigmine prior to recovery. Objective recovery events were recorded and subjective visual analogue scale scores of recovery quality were assigned from video recordings.

RESULTS

Recovery measures in phase 1 were not different between horses receiving neostigmine or saline solution. In phase 2A, 0.04 mg of physostigmine/kg was the highest cumulative dose that did not cause clinically relevant adverse behavioral or gastrointestinal effects. Horses receiving physostigmine had higher mean ± SD visual analogue scale recovery scores (70.8 ± 13.3 mm) than did horses receiving neostigmine (62.4 ± 12.8 mm) in phase 2B, with fewer attempts until sternal and standing recovery. Incidence of colic behavior did not differ among groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Inhibition with physostigmine improved anesthetic recovery quality in horses anesthetized with isoflurane, compared with recovery quality for horses receiving neostigmine. Inhibition of central muscarinic receptors by inhalation anesthetics may underlie emergence delirium in horses recovering from anesthesia.

Propofol Limits Microglial Activation after Experimental Brain Trauma through Inhibition of Nicotinamide Adenine Dinucleotide Phosphate Oxidase

Background:

Microglial activation is implicated in delayed tissue damage after traumatic brain injury (TBI). Activation of microglia causes up-regulation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, with the release of reactive oxygen species and cytotoxicity. Propofol appears to have antiinflammatory actions. The authors evaluated the neuroprotective effects of propofol after TBI and examined in vivo and in vitro whether such actions reflected modulation of NADPH oxidase.

Methods:

Adult male rats were subjected to moderate lateral fluid percussion TBI. Effect of propofol on brain microglial activation and functional recovery was assessed up to 28 days postinjury. By using primary microglial and BV2 cell cultures, the authors examined propofol modulation of lipopolysaccharide and interferon-γ–induced microglial reactivity and neurotoxicity.

Results:

Propofol improved cognitive recovery after TBI in novel object recognition test (48 ± 6% for propofol [n = 15] vs. 30 ± 4% for isoflurane [n = 14]; P = 0.005). The functional improvement with propofol was associated with limited microglial activation and decreased cortical lesion volume and neuronal loss. Propofol also attenuated lipopolysaccharide- and interferon-γ–induced microglial activation in vitro, with reduced expression of inducible nitric oxide synthase, nitric oxide, tumor necrosis factor-α, interlukin-1β, reactive oxygen species, and NADPH oxidase. Microglial-induced neurotoxicity in vitro was also markedly reduced by propofol. The protective effect of propofol was attenuated when the NADPH oxidase subunit p22phox was knocked down by small interfering RNA. Moreover, propofol reduced the expression of p22phox and gp91phox, two key components of NADPH oxidase, after TBI.

Conclusion:

The neuroprotective effects of propofol after TBI appear to be mediated, in part, through the inhibition of NADPH oxidase.

[Postoperative cognitive dysfunction. Possible neuronal mechanisms and practical consequences for clinical routine]

Postoperative cognitive dysfunction (POCD) presents as a long-lasting decline in cognitive function after a surgical procedure, predominantly occurring in elderly patients. The causes are most likely multifactorial with the exact mechanisms still unknown. Hypotheses of the causes of POCD are based on experimental evidence that anesthetics can impair mechanisms of learning and memory on a neuronal level and might lead to neurodegeneration. Additionally, surgery can result in neuroinflammation which could also underlie POCD. The most important strategy to avoid POCD is to maintain the patient's physiological homeostasis perioperatively. According to the presently available clinical studies recommendations in favor or against certain anesthesiological procedures cannot be given.

[Propofol-induced myocardial depression: possible role of atrial muscarinic cholinergic receptors]

OBJECTIVE

To investigate the possible role of muscarinic cholinergic receptors (MCRs) in the depression of myocardial function induced by propofol, an intravenous anesthetic chemically unrelated to other drugs. Although adverse effects are rare, bradycardia has been reported and this can lead to cardiac arrest in some patients. The mechanism behind this effect is still unknown but a possible role for MCRs has been suggested.

MATERIAL AND METHODS

The interaction of propofol with human atrial MCRs was determined by means of inhibition tests using [3H] quinuclidinyl benzilate ([3H] QNB).

RESULTS

The displacement of [3H] QNB binding to human atrial MCRs by propofol was concentration dependent but the observed effect was not consistent with a model of simple competition between propofol and [3H] QNB.

CONCLUSION

Propofol appears to have the ability to modify the activity of human atrial MCRs and this effect may be related to its ability to induce bradycardia.

Oocytes as an expression system for studying receptor/channel targets of drugs and pesticides

The Xenopus laevis oocyte offers one of the most convenient expression systems for assaying the actions of candidate ligands on cloned ionotropic neurotransmitter receptors (also known as ligand-gated ion channels [LGICs]). Their large size makes injection of complementary ribonucleic acid or complementary deoxyribonucleic acid and electrophysiological recording very easy. Furthermore, Xenopus oocytes translate messages very efficiently, resulting in the detection of large-amplitude ligand-induced currents from expressed, recombinant LGICs. Compared to other electrophysiological techniques, recording from oocytes is not difficult and requires only a basic electrophysiological recording setup. Oocytes can be used for two-electrode voltage clamp, as well as cell-attached patch and inside- or outside-out patch clamp recordings. A variety of protocols allows the experimenter to determine the actions of ligands on cloned receptors and parameters, such as their affinity, efficacy, rates of association and desensitization, and reversibility, to be estimated. Here, we present protocols for using Xenopus oocytes in assaying candidate ligands acting against cloned targets of drugs and pesticides.

Drugs of anesthesia acting on central cholinergic system may cause post-operative cognitive dysfunction and delirium

Given the progressive and constant increase of average life expectancy, an increasing number of elderly patients undergo surgery. After surgery, elderly patients often exhibit a transient reversible state of cerebral cognitive alterations. Among these cognitive dysfunctions, a state of delirium may develop. Delirium is an aetiologically non-specific syndrome characterised by concurrent disturbances of consciousness and attention, perception, thinking, memory, psychomotor behaviour and the sleep-wake cycle. Delirium appears to occur in 10-26% of general medical patients over 65, and is frequently associated with a significant increase in morbidity and mortality. During hospitalization, mortality rates have been estimated to be 10-26% of patients who developed post-operative delirium, and 22-76% during the following months. Over the last few decades, post-operative delirium has been associated with several pre-operative predictor factors, as well as age (50 years and older), alcohol abuse, poor cognitive and functional status, electrolyses or glucose abnormalities, and type of surgery. The uncertain pathogenesis of post-operative cognitive dysfunctions and delirium has not permitted a causal approach to developing an effective treatment. General anesthesia affects brain function at all levels, including neuronal membranes, receptors, ion channels, neurotransmitters, cerebral blood flow and metabolism. The functional equivalents of these impairments involve mood, memory, and motor function behavioural changes. These dysfunctions are much more evident in the occurrence of stress-regulating transmission and in the alteration of intra-cellular signal transduction systems. In addition, more essential cellular processes, that play an important role in neurotransmitter synthesis and release, such as intra-neuronal signal transduction and second messenger system, may be altered. Keeping in mind the functions of the central muscarinic cholinergic system and its multiple interactions with drugs of anesthesia, it seems possible to hypothesize that the inhibition of muscarinic cholinergic receptors could have a pivotal role in the pathogenesis not only of post-operative delirium but also the more complex phenomena of post-operative cognitive dysfunction.

Muscarinic M2 and M4 receptors in anterior cingulate cortex: relation to neuropsychiatric symptoms in dementia with Lewy bodies

Alterations in cholinergic functions have been reported to be associated with neuropsychiatric symptoms in dementia. Increased M1 muscarinic receptor binding in temporal cortex is associated with delusions in dementia with Lewy bodies (DLB) patients and increased M2/M4 receptor binding with psychosis in Alzheimer's disease. However, the relation between M2 and M4 muscarinic receptor and psychotic symptoms in DLB is unknown. The aim of this study was to measure M2 and M4 receptors in the anterior cingulate cortex in DLB and to correlate the neurochemical findings with neuropsychiatric symptoms. Muscarinic M2 and M4 receptor levels in the anterior cingulate cortex and adjacent cortex (Brodmann's area [BA] 32) were measured separately by using a radioligand binding protocol based on binding of [(3)H]AF-DX 384 in the presence and absence of dicyclomine, a potent M4 receptor antagonist. M2 receptor binding was significantly increased, while M4 receptor binding was unchanged in the cingulate cortex and BA32 of DLB patients compared with age-matched controls. Impaired consciousness was significantly associated with increased M4 binding and delusions were significantly associated with increased M2 binding. Increased M2 and M4 receptor binding in DLB was also associated with visual hallucinations. Upregulation of M2 and M4 muscarinic receptors in cingulate and adjacent cortex may thus contribute to the development of psychosis in DLB, with potential implications for treatments with drugs acting on these receptors.