Molecular Actions of Propofol on Human 5-HT3A Receptors: Enhancement as Well as Inhibition by Closely Related Phenol Derivatives

Risk factors for postoperative delirium in patients undergoing orthopedic procedures: a systematic review and meta-analysis

Delirium is a common complication in surgical patients following operative procedures; it often occurs in patients undergoing lower-extremity surgery. It is essential to identify and prevent the risk factors for postoperative delirium (POD) in these cases. We aimed to determine the risk factors for POD in patients who underwent lower-extremity surgery through a systematic review and meta-analysis. We included observational studies identifying risk factors for POD in patients undergoing orthopedic surgery. Data sources included the Cumulative Index to Nursing and Allied Health Literature and MEDLINE. We extracted the variables related to delirium that were analyzed by two or more studies meeting the eligibility criteria. A random-effects model was used to calculate the pooled odds ratio, standardized mean difference, and 95% confidence interval. Data were considered significant when p <  0.05. Twenty-seven studies with a total sample size of 9,044 were evaluated. Our meta-analysis revealed 20 risk factors for patients with POD undergoing orthopedic surgery, including age, cognitive scores, various preoperative laboratory values (such as serum albumin, C-reactive protein, and thyroid hormones), length of hospital stay, surgery and anesthesia duration, blood transfusion, and previous health conditions such as dementia and cardiovascular disease. Gathering preoperative and postoperative data was crucial for identifying high-risk patients for POD. In addition, preventive measures targeting POD risk factors could reduce its occurrence after orthopedic surgery.

The risk factors for postoperative delirium in adult patients after hip fracture surgery: a systematic review and meta-analysis

OBJECTIVES

Postoperative delirium (POD) is the most common complication in patients after hip fracture surgery, and the incidence of POD is associated with mortality and disability in patients following hip fracture surgery. Therefore, this study aimed to identify the individual as well as anesthetic and operative risk factors associated with the POD in adult patients after hip fracture surgery.

METHODS

We searched relevant articles published to February 2020 in Cochrane Library, PubMed, and Embase. Studies involving adult patients who underwent hip fracture surgery were regarded as relevant if the studies contained the individual or anesthetic and surgical characteristics of participants. The pooled relative risk ratios (RRs) or weight mean difference of the variables were estimated by the Mantel-Haenszel or Inverse-Variance methods.

RESULTS

A total of 44 studies were included, which altogether included 104572 participants with hip fracture surgery (17703 patients with POD and 86869 patients without POD) and the incidence of POD was 16.93%. A total of 14 risk factors, classified into two categories which were individual as well as anesthetic and operative factors, were identified originally, which included age (weight mean difference [WMD]:2.33;95% confidential interval [CI]: 1.64-3.03), sex (RR: 0.89; 95% CI:0.85-0.93), American society of Anesthesiologists classification(RR:0.56; 95%CI:0.51-0.59), body mass index (WMD:-0.62; 95%CI:-0.81 to -0.44), function dependency(RR:1.52; 95% CI:1.24-1.87), visual impairment (RR:1.62; 95% CI: 1.16-2.27), smoking (RR:0.86; 95% CI:0.79-0.94), preoperative delirium (RR: 2.71; 95% CI: 2.50-2.72), dementia (RR:2.60; 95% CI:2.50-2.72), hypertension (RR: 1.10; 95% CI:1.04-1.15), chronic obstructive pulmonary disease (RR:1.08; 95% CI: 1.01-1.16), regional anesthesia (RR:1.20; 95% CI: 1.01-1.43), transfusion (RR: 1.41; 95% CI: 1.22-1.63), and elective surgery (RR: 0.91; 95% CI: 0.84-0.99).

CONCLUSIONS

Patients possessed above risk factors might be high-risk patients. Clinician should maintain keen vigilance at those patients.

Region specific differences in the effect of propofol on the murine colon result in dysmotility

Propofol is the most widely used intravenous anaesthetic agent for maintenance of anaesthesia and sedation. Studies in varying regions of the bowel have shown conflicting differences on the effects of propofol on motility. There the aim of this study was to understand the influence of propofol on colonic function and explore by which mechanism any changes occur. Functional studies were conducted using isolated colonic tissue from C57BL6 mice which were exposed to 5 μM propofol. Faecal pellet motility, colonic migratory motor complexes (CMMCs) and functional bioassays were utilised to monitor colonic function and nitric oxide production was monitored by amperometry. There was a signficant reduction in amplitude of CMMCs in the distal colon in the presence of 5 μM propofol, however no difference was observed in the proximal colon. A signficant increase in the 5-HT evoked contractions were observed in distal colon in the presence of 5 μM propofol. Additionally, a reduction in the NO production in the presence of 5 μM propofol was only observed in the distal colon. As a result, in the presence of 5 μM propofol, faecal pellet transit was increased, and velocity was reduced. At clinically relevant doses, propofol was shown to reduce colonic motility by inhibiting nitric oxide synthase in only the distal region of the colon. Our findings indicate that propofol has a considerable influence on colonic signalling mechanisms and impairs colonic motility, which may have implications in its clinical use especially for maintenance.

A personality trait contributes to the occurrence of postoperative delirium: a prospective study

BACKGROUND

Although various physical risk factors for delirium have been identified, the effect of psychological aspects is currently unknown. This study aimed to examine psychological risk factors for postoperative delirium and to identify hidden subgroups of delirium in clinical and psychological feature space.

METHODS

Among 200 patients with hip fracture, 78 elderly patients were prospectively evaluated for clinical and psychological assessments before surgery. As delirium was assessed from the next day to the 7th day after surgery, postoperative delirium was found in 40 patients, but not in 38 patients. Univariate and multivariate logistic regression analyses were used to explore risk factors for postoperative delirium. Phenotypic subgroups of delirium were assessed using Topological Data Analysis, in which the significant risk factors were used for evaluating filter and distance metrics.

RESULTS

Mini-Mental State Examination, neuroticism, conscientiousness, and regional anesthesia were identified as a predictive risk factor for postoperative delirium. The filter metric showed significant negative correlations with nutrition-related factors such as total protein and albumin. When filter metric and Euclidean distances were entered, delirious patients were bifurcated as a function of personality traits and anesthesia method in the patient-patient network.

CONCLUSIONS

A personality trait of neuroticism and conscientiousness may predispose elderly patients to postoperative delirium and this influence may be amplified by regional anesthesia. This study verifies the contribution of psychological risk factors to delirium and provides new insight for complex etiologies of delirium by mapping various clinical variables in the topological space.

Kampo Medicine: Evaluation of the Pharmacological Activity of 121 Herbal Drugs on GABAA and 5-HT3A Receptors

Kampo medicine is a form of Japanese phytotherapy originating from traditional Chinese medicine (TCM). During the last several decades, much attention has been paid to the pharmacological effects of these medical plants and their constituents. However, in many cases, a systematic screening of Kampo remedies to determine pharmacologically relevant targets is still lacking. In this study, a broad screening of Kampo remedies was performed to look for pharmacologically relevant 5-HT_3A and GABA_A receptor ligands. Several of the Kampo remedies are currently used for symptoms such as nausea, emesis, gastrointestinal motility disorders, anxiety, restlessness, or insomnia. Therefore, the pharmacological effects of 121 herbal drugs from Kampo medicine were analyzed as ethanol tinctures on heterologously expressed 5-HT_3A and GABA_A receptors, due to the involvement of these receptors in such pathophysiological processes. The tinctures of Lindera aggregata (radix) and Leonurus japonicus (herba) were the most effective inhibitory compounds on the 5-HT_3A receptor. Further investigation of known ingredients in these compounds led to the identification of leonurine from Leonurus as a new natural 5-HT_3A receptor antagonist. Several potentiating herbs (e.g., Magnolia officinalis (cortex), Syzygium aromaticum (flos), and Panax ginseng (radix)) were also identified for the GABA_A receptor, which are all traditionally used for their sedative or anxiolytic effects. A variety of tinctures with antagonistic effects Salvia miltiorrhiza (radix) were also detected. Therefore, this study reveals new insights into the pharmacological action of a broad spectrum of herbal drugs from Kampo, allowing for a better understanding of their physiological effects and clinical applications.

Identification of Glycyrrhiza as the rikkunshito constituent with the highest antagonistic potential on heterologously expressed 5-HT3A receptors due to the action of flavonoids

The traditional Japanese phytomedicine rikkunshito is traditionally used for the treatment of gastrointestinal motility disorders, cachexia and nausea. These effects indicate 5-HT₃ receptor antagonism, due to the involvement of these receptors in such pathophysiological processes. E.g., setrons, specific 5-HT₃ receptor antagonists are the strongest antiemetics, developed so far. Therefore, the antagonistic effects of the eight rikkunshito constituents at heterologously expressed 5-HT_3Areceptors were analyzed using the two-electrode voltage-clamp technique. The results indicate that tinctures from Aurantii, Ginseng, Zingiberis, Atractylodis and Glycyrrhiza inhibited the 5-HT_3A receptor response, whereas the tinctures of Poria cocos, Jujubae and Pinellia exhibited no effect. Surprisingly, the strongest antagonism was found for Glycyrrhiza, whereas the Zingiberis tincture, which is considered to be primarily responsible for the effect of rikkunshito, exhibited the weakest antagonism of 5-HT_3A receptors. Rikkunshito contains various vanilloids, ginsenosides and flavonoids, a portion of which show an antagonistic effect on 5-HT₃ receptors. A screening of the established ingredients of the active rikkunshito constituents and related substances lead to the identification of new antagonists within the class of flavonoids. The flavonoids (-)-liquiritigenin, glabridin and licochalcone A from Glycyrrhiza species were found to be the most effective inhibitors of the 5-HT-induced currents in the screening. The flavonoids (-)-liquiritigenin and hesperetin from Aurantii inhibited the receptor response in a non-competitive manner, whereas glabridin and licochalcone A exhibited a potential competitive antagonism. Furthermore, licochalcone A acts as a partial antagonist of 5-HT_3A receptors. Thus, this study reveals new 5-HT_3A receptor antagonists with the aid of increasing the comprehension of the complex effects of rikkunshito.

Fast and slow interactions of n-alkanols with human 5-HT3A receptors: Implications for anesthetic mechanisms

This is part of a continuing patch-clamp study exploring molecular actions of anesthetics and systematically varied related substances on 5-HT3A receptors as prototypes of ligand-gated ion channels. Specifically, n-alkanols, related to but simpler in structure than propofol, were studied to explore the complex actions of this leading intravenous anesthetic. Outside-out patches excised from HEK 293 cells heterologously expressing human 5-HT3A receptors were superfused with even-numbered n-alkanols (ethanol through n-tetradecanol) of different concentrations. Fast solution exchange for varying durations allowed separation of drug actions by their kinetics. Compared with propofol the electrophysiological responses to n-alkanols were not much simpler. n-Alkanols produced fast and slow inhibition or potentiation of current amplitudes, and acceleration of current rise and decay time constants, depending on exposure time, concentration, and chain-length of the drug. Inhibition dominated, characterized by fast and slow processes with time constants separated by two orders of magnitude which were similar for different n-alkanols and for propofol. Absolute interaction energies for ethanol to n-dodecanol (relative to xenon) ranged from -10.8 to -37.3kJmol(-1). No two n-alkanols act completely alike. Potency increases with chain length (until cutoff) mainly because of methylene groups interacting with protein sites rather than because of their tendency to escape from the aqueous phase. Similar wash-in time constants for n-alkanols and propofol suggest similar mechanisms, dominated by the kinetics of conformational state changes rather than by binding reactions.

Activation of human 5-hydroxytryptamine type 3 receptors via an allosteric transmembrane site

In common with other members of the Cys-loop family of pentameric ligand-gated ion channels, 5-hydroxytryptamine type 3 receptors (5-HT3Rs) are activated by the binding of a neurotransmitter to an extracellular orthosteric site, located at the interface of two adjacent receptor subunits. In addition, a variety of compounds have been identified that modulate agonist-evoked responses of 5-HT3Rs, and other Cys-loop receptors, by binding to distinct allosteric sites. In this study, we examined the pharmacological effects of a group of monoterpene compounds on recombinant 5-HT3Rs expressed in Xenopus oocytes. Two phenolic monoterpenes (carvacrol and thymol) display allosteric agonist activity on human homomeric 5-HT3ARs (64 ± 7% and 80 ± 4% of the maximum response evoked by the endogenous orthosteric agonist 5-HT, respectively). In addition, at lower concentrations, where agonist effects are less apparent, carvacrol and thymol act as potentiators of responses evoked by submaximal concentrations of 5-HT. By contrast, carvacrol and thymol have no agonist or potentiating activity on the closely related mouse 5-HT3ARs. Using subunit chimeras containing regions of the human and mouse 5-HT3A subunits, and by use of site-directed mutagenesis, we have identified transmembrane amino acids that either abolish the agonist activity of carvacrol and thymol on human 5-HT3ARs or are able to confer this property on mouse 5-HT3ARs. By contrast, these mutations have no significant effect on orthosteric activation of 5-HT3ARs by 5-HT. We conclude that 5-HT3ARs can be activated by the binding of ligands to an allosteric transmembrane site, a conclusion that is supported by computer docking studies.

Tropisetron alleviate early post-operative pain after gynecological laparoscopy in sevoflurane based general anaesthesia: a randomized, parallel-group, factorial study

BACKGROUND

Studies have suggested that 5-hydroxytryptamine-3A (5-HT-3A) receptor antagonists may have analgesic effects. This randomized, double-blind, placebo-controlled, factorial study tested the hypothesis that 5-HT-3A receptor antagonist tropisetron attenuates post-operative pain in women receiving either sevoflurane or propofol based anaesthesia.

METHODS

Two hundred and ninety-six women undergoing gynaecological laparoscopies were randomly assigned to be anaesthetized with either sevoflurane or propofol. Immediately after the induction of anaesthesia, the anaesthesiologist administered either tropisetron 2 mg or a placebo intravenously. Pain score at rest at 0.5 h post-operatively reported using a numerical rating scale was the primary outcome measure. The secondary outcome measures included pain score at rest every 2 h within the first 24 h post-operatively, duration of post-anaesthesia care unit stay, incidence of post-operative nausea and vomiting, the incidence of shivering and score of the Quality of Recovery Score 40.

RESULTS

Compared with placebo, tropisetron produced a statistically significant decrease on pain report within the first 6 h post-operatively in the sevoflurane-based anaesthesia group (3 [2, 4] vs. 5 [4, 5], p < 0.001 in 0.5 h; 2 [0, 4] vs. 3 [3, 5], p < 0.001 in 2 h; 2 [0, 3] vs. 3 [1, 4], p = 0.002 in 4 h; 1 [0, 3] vs. 2 [1, 4], p = 0.016 in 6 h), but not in the propofol-based group.

CONCLUSIONS

A single-dose intravenous administration of tropisetron after anaesthesia induction is associated with statistically significant decreased early post-operative pain in patients undergoing gynaecological laparoscopies under sevoflurane based general anaesthesia.

Molecular interactions between general anesthetics and the 5HT2B receptor

BACKGROUND

Serotonin modulates many processes through a family of seven serotonin receptors. However, no studies have screened for interactions between general anesthetics currently in clinical use and serotonergic G-protein-coupled receptors (GPCRs). Given that both intravenous and inhalational anesthetics have been shown to target other classes of GPCRs, we hypothesized that general anesthetics might interact directly with some serotonin receptors and thus modify their function.

METHODS

Radioligand binding assays were performed to screen serotonin receptors for interactions with propofol and isoflurane as well as for affinity determinations. Docking calculations using the crystal structure of 5-HT2B were performed to computationally confirm the binding assay results and locate anesthetic binding sites.

RESULTS

The 5-HT2B class of receptors interacted significantly with both propofol and isoflurane in the primary screen. The affinities for isoflurane and propofol were determined to be 7.78 and .95 μM, respectively, which were at or below the clinical concentrations for both anesthetics. The estimated free energy derived from docking calculations for propofol (-6.70 kcal/mol) and isoflurane (-5.10 kcal/mol) correlated with affinities from the binding assay. The anesthetics were predicted to dock at a pharmacologically relevant binding site of 5HT2B.

CONCLUSIONS

The molecular interactions between propofol and isoflurane with the 5-HT2B class of receptors were discovered and characterized. This finding implicates the serotonergic GPCRs as potential anesthetic targets.

Anaesthetic agents for thoracic surgery: what's best?

PURPOSE OF REVIEW

Pneumonectomy is still associated with a 5% 30-day mortality in a large series involving a variety of anaesthetic agents and techniques.

RECENT FINDINGS

As well as the immediate 'anaesthetic' complications of pain, nausea and vomiting and respiratory dysfunction, differences between anaesthetic agents have emerged in systemic inflammation, postoperative cognitive dysfunction, immune suppression and cell signalling after surgery.

SUMMARY

No one anaesthetic agent has emerged as best. There is a trade-off between initial success and long-term problems or vice versa.

Which agonist properties are important for the activation of 5-HT3A receptors?

PURPOSE

Why do anesthetics not activate excitatory ligand-gated ion channels such as 5-HT3 receptors in contrast to inhibitory ligand-gated ion channels? This study examines the actions of structural closely-related 5-HT derivatives and 5-HT constituent parts on 5-HT3A receptors with the aim of finding simpler if not minimal agonists and thus determining requirements for successful agonist action.

EXPERIMENTAL APPROACH

Responses to 5-HT derivatives of human 5-HT3A receptors stably expressed in HEK 293 cells have been examined with the patch-clamp technique in the outside-out configuration combined with a fast solution exchange system.

RESULTS

Phenol, pyrrole and alkyl amines, constituents of 5-HT, even at high concentrations, cannot activate 5-HT3A receptors but they can inhibit them. To date, tyramines are the smallest known agonists. However, an aromatic ring is not required for activation as acetylcholine is also an agonist of similar strength.

CONCLUSION

Simultaneous interactions of adequate strength at two separate subsites within the 5-HT binding domain appear to be essential for successful agonist function. Anesthetics either fail to achieve this or the activation they produce is so weak that it is masked by a comparatively very strong inhibition.

Asymmetric ligand binding facilitates conformational transitions in pentameric ligand-gated ion channels

The anesthetic propofol inhibits the currents of the homopentameric ligand-gated ion channel GLIC, yet the crystal structure of GLIC with five propofol molecules bound symmetrically shows an open-channel conformation. To address this dilemma and determine if the symmetry of propofol binding sites affects the channel conformational transition, we performed a total of 1.5 μs of molecular dynamics simulations for different GLIC systems with propofol occupancies of 0, 1, 2, 3, and 5. GLIC without propofol binding or with five propofol molecules bound symmetrically, showed similar channel conformation and hydration status over multiple replicates of 100-ns simulations. In contrast, asymmetric binding to one, two or three equivalent sites in different subunits accelerated the channel dehydration, increased the conformational heterogeneity of the pore-lining TM2 helices, and shifted the lateral and radial tilting angles of TM2 toward a closed-channel conformation. The results differentiate two groups of systems based on the propofol binding symmetry. The difference between symmetric and asymmetric groups is correlated with the variance in the propofol-binding cavity adjacent to the hydrophobic gate and the force imposed by the bound propofol. Asymmetrically bound propofol produced greater variance in the cavity size that could further elevate the conformation heterogeneity. The force trajectory generated by propofol in each subunit over the course of a simulation exhibits an ellipsoidal shape, which has the larger component tangential to the pore. Asymmetric propofol binding creates an unbalanced force that expedites the channel conformation transitions. The findings from this study not only suggest that asymmetric binding underlies the propofol functional inhibition of GLIC, but also advocate for the role of symmetry breaking in facilitating channel conformational transitions.

Allosteric modulation of the 5-HT(3) receptor

5-Hydroxytryptamine type 3 (5-HT(3)) receptors are ligand-gated ion channels that play important roles in depression, anxiety, substance abuse, emesis, inflammatory pain, spinal nociception, gastrointestinal function, and cardiovascular reflexes. Probably the most studied modulators of 5-HT(3) receptors are the high affinity competitive 'setron' antagonists typified by ondansetron. However, there exists a broad range of compounds that modulate the 5-HT(3) receptor, not through the orthosteric site but by binding to allosteric sites. Most notable are therapeutic compounds ascribed to certain targets but that allosterically modulate 5-HT(3) receptors at clinically relevant concentrations.

5-HT(3) receptors: role in disease and target of drugs

Serotonin type 3 (5-HT(3)) receptors are pentameric ion channels belonging to the superfamily of Cys-loop receptors. Receptor activation either leads to fast excitatory responses or modulation of neurotransmitter release depending on their neuronal localisation. 5-HT(3) receptors are known to be expressed in the central nervous system in regions involved in the vomiting reflex, processing of pain, the reward system, cognition and anxiety control. In the periphery they are present on a variety of neurons and immune cells. 5-HT(3) receptors are known to be involved in emesis, pain disorders, drug addiction, psychiatric and GI disorders. Progress in molecular genetics gives direction to personalised medical strategies for treating complex diseases such as psychiatric and functional GI disorders and unravelling individual drug responses in pharmacogenetic approaches. Here we discuss the molecular basis of 5-HT(3) receptor diversity at the DNA and protein level, of which our knowledge has greatly extended in the last decade. We also evaluate their role in health and disease and describe specific case-control studies addressing the involvement of polymorphisms of 5-HT3 subunit genes in complex disorders and responses to drugs. Furthermore, we focus on the actual state of the pharmacological knowledge concerning not only classical 5-HT(3) antagonists--the setrons--but also compounds of various substance classes targeting 5-HT(3) receptors such as anaesthetics, opioids, cannabinoids, steroids, antidepressants and antipsychotics as well as natural compounds derived from plants. This shall point to alternative treatment options modulating the 5-HT(3) receptor system and open new possibilities for drug development in the future.

Propofol abolished the phrenic long-term facilitation in rats

The aim was to investigate the effect of propofol anesthesia on the phrenic long-term facilitation (pLTF) in rats. We hypothesized that pLTF would be abolished during propofol-compared with urethane anesthesia. Fourteen adult, male, anesthetized, vagotomized, paralyzed, and mechanically ventilated Sprague-Dawley rats (seven per group), were exposed to the acute intermittent hypoxia (AIH) protocol. Peak phrenic nerve activity (PNA), burst frequency (f), and breathing rhythm parameters (Ti, Te, Ttot) were analyzed during the first hypoxia (TH1), as well as at 15 (T15), 30 (T30), and 60min (T60) after the final hypoxic episode, and compared to the baseline values. In propofol-anesthetized rats no significant changes of PNA were recorded after the last hypoxic episode, i.e. no pLTF was induced. There was a significant increase of PNA (59.4+/-6.6%, P<0.001) in urethane-anesthetized group at T60. AIH did not elicit significant changes in f, Ti, Te, Ttot in either group at T15, T30, and T60. The pLTF, elicited by AIH, was induced in the urethane-anesthetized rats. On the contrary, pLTF was abolished in the propofol-anesthetized rats.

Selective micro preconcentration of propofol for anesthetic depth monitoring by using seedless electroplated gold as adsorbent

This communication presents selective preconcentration of the anesthetic agent (Propofol) and the elimination of unwanted species from a representative sample of human breath. In this approach, a micro preconcentrator (microPC) consisting of embedded high-aspect-ratio pillars (30 microm x 120 microm chi 240 microm), an outer dimensions of 7 mm x 7 mm (encompass more than 3500 micro pillars), total inner surface area of approximately 10 m(2), and a total inner volume of approximately 6.5 microL was used to selectively preconcentrate Propofol. The microPC has on-chip thermal desorption capability and was coated by electrodeposited gold as an adsorbent material. Experimental evaluations showed successful preconcentration of trace level of Propofol from a mixture containing several volatile organic compounds diluted in water-like solvent (1-propanol) and the efficient removal of non-polar compounds present in the mixture.