A hypothesis about the endogenous analogue of general anesthesia

Anesthetic Mechanisms: Synergistic Interactions With Lipid Rafts and Voltage-Gated Sodium Channels

Despite successfully utilizing anesthetics for over 150 years, the mechanism of action remains relatively unknown. Recent studies have shown promising results, but due to the complex interactions between anesthetics and their targets, there remains a clear need for further mechanistic research. We know that lipophilicity is directly connected to anesthetic potency since lipid solubility relates to anesthetic partition into the membrane. However, clinically relevant concentrations of anesthetics do not significantly affect lipid bilayers but continue to influence various molecular targets. Lipid rafts are derived from liquid-ordered phases of the plasma membrane that contain increased concentrations of cholesterol and sphingomyelin and act as staging platforms for membrane proteins, including ion channels. Although anesthetics do not perturb membranes at clinically relevant concentrations, they have recently been shown to target lipid rafts. In this review, we summarize current research on how different types of anesthetics-local, inhalational, and intravenous-bind and affect both lipid rafts and voltage-gated sodium channels, one of their major targets, and how those effects synergize to cause anesthesia and analgesia. Local anesthetics block voltage-gated sodium channel pores while also disrupting lipid packing in ordered membranes. Inhalational anesthetics bind to the channel pore and the voltage-sensing domain while causing an increase in the number, size, and diameter of lipid rafts. Intravenous anesthetics bind to the channel primarily at the voltage-sensing domain and the selectivity filter, while causing lipid raft perturbation. These changes in lipid nanodomain structure possibly give proteins access to substrates that have translocated as a result of these structural alterations, resulting in lipid-driven anesthesia. Overall, anesthetics can impact channel activity either through direct interaction with the channel, indirectly through the lipid raft, or both. Together, these result in decreased sodium ion flux into the cell, disrupting action potentials and producing anesthetic effects. However, more research is needed to elucidate the indirect mechanisms associated with channel disruption through the lipid raft, as not much is known about anionic lipid products and their influence over voltage-gated sodium channels. Anesthetics' effect on S-palmitoylation, a promising mechanism for direct and indirect influence over voltage-gated sodium channels, is another auspicious avenue of research. Understanding the mechanisms of different types of anesthetics will allow anesthesiologists greater flexibility and more specificity when treating patients.

Effects of mid‑gestational sevoflurane and magnesium sulfate on maternal oxidative stress, inflammation and fetal brain histopathology

Models of inflammation, oxidative stress, hyperoxia and hypoxia have demonstrated that magnesium sulfate (MgSO4), a commonly used drug in obstetrics, has neuroprotective potential. In the present study, the effects of MgSO4 treatment on inflammation, oxidative stress and fetal brain histopathology were evaluated in an experimental rat model following sevoflurane (Sv) exposure during the mid-gestational period. Rats were randomly divided into groups: C (control; no injections or anesthesia), Sv (exposure to 2.5% Sv for 2 h), MgSO4 (administered 270 mg/kg MgSO4 intraperitoneally) and Sv + MgSO4 (Sv administered 30 min after MgSO4 injection). Inflammatory and oxidative stress markers were measured in the serum and neurotoxicity was investigated histopathologically in fetal brain tissue. Short-term mid-gestational exposure to a 1.1 minimum alveolar concentration of Sv did not significantly increase the levels of any of the measured biochemical markers, except for TNF-α. Histopathological evaluations demonstrated no findings suggestive of pathological apoptosis, neuroinflammation or oxidative stress-induced cell damage. MgSO4 injection prior to anesthesia caused no significant differences in biochemical or histopathological marker levels compared to the C and Sv groups. The present study indicated that short-term exposure to Sv could potentially be considered a harmless external stimulus to the fetal brain.

Inhalation of hydrogen gas mitigates sevoflurane-induced neuronal apoptosis in the neonatal cortex and is associated with changes in protein phosphorylation

Inhalation of hydrogen (H2) gas is therapeutically effective for cerebrovascular diseases, neurodegenerative disorders, and neonatal brain disorders including pathologies induced by anesthetic gases. To understand the mechanisms underlying the protective effects of H2 on the brain, we investigated the molecular signals affected by H2 in sevoflurane-induced neuronal cell death. We confirmed that neural progenitor cells are susceptible to sevoflurane and undergo apoptosis in the retrosplenial cortex of neonatal mice. Co-administration of 1-8% H2 gas for 3 h to sevoflurane-exposed pups suppressed elevated caspase-3-mediated apoptotic cell death and concomitantly decreased c-Jun phosphorylation and activation of the c-Jun pathway, all of which are induced by oxidative stress. Anesthesia-induced increases in lipid peroxidation and oxidative DNA damage were alleviated by H2 inhalation. Phosphoproteome analysis revealed enriched clusters of differentially phosphorylated proteins in the sevoflurane-exposed neonatal brain that included proteins involved in neuronal development and synaptic signaling. H2 inhalation modified cellular transport pathways that depend on hyperphosphorylated proteins including microtubule-associated protein family. These modifications may be involved in the protective mechanisms of H2 against sevoflurane-induced neuronal cell death.

Diethyl ether anesthesia induces transient cytosolic [Ca2+] increase, heat shock proteins, and heat stress tolerance of photosystem II in Arabidopsis

General volatile anesthetic diethyl ether blocks sensation and responsive behavior not only in animals but also in plants. Here, using a combination of RNA-seq and proteomic LC-MS/MS analyses, we investigated the effect of anesthetic diethyl ether on gene expression and downstream consequences in plant Arabidopsis thaliana. Differential expression analyses revealed reprogramming of gene expression under anesthesia: 6,168 genes were upregulated, 6,310 genes were downregulated, while 9,914 genes were not affected in comparison with control plants. On the protein level, out of 5,150 proteins identified, 393 were significantly upregulated and 227 were significantly downregulated. Among the highest significantly downregulated processes in etherized plants were chlorophyll/tetrapyrrole biosynthesis and photosynthesis. However, measurements of chlorophyll a fluorescence did not show inhibition of electron transport through photosystem II. The most significantly upregulated process was the response to heat stress (mainly heat shock proteins, HSPs). Using transgenic A. thaliana expressing APOAEQUORIN, we showed transient increase of cytoplasmic calcium level [Ca²⁺]_cyt in response to diethyl ether application. In addition, cell membrane permeability for ions also increased under anesthesia. The plants pre-treated with diethyl ether, and thus with induced HSPs, had increased tolerance of photosystem II to subsequent heat stress through the process known as cross-tolerance or priming. All these data indicate that diethyl ether anesthesia may partially mimic heat stress in plants through the effect on plasma membrane.

Effects of Sevoflurane Anesthesia on Cerebral Lipid Metabolism in the Aged Brain of Marmosets and Mice

Objective

In the lipid-rich brain, lipids performed signaling processes associated with the control system of the cell cycle, stress, and inflammatory reactions, as well as maintained brain and cellular homeostasis. The effects of general anesthesia on brain impairment in the elderly were controversial and complex. The study sought to evaluate the effect of lipid metabolism in the brain of aged marmosets and mice under long-term exposure to sevoflurane.

Methods

A total of 6 marmosets over 8-year-old and 10 mice aged 18 months were divided into the sevoflurane anesthesia and control groups, respectively. Marmosets in the sevoflurane anesthesia group were exposed to 1.5–2.5% sevoflurane and 100% O₂ for 6 h. Mice anesthetized with sevoflurane were exposed to 3% sevoflurane and 60% O₂ for 6 h. All prefrontal cortex tissues of marmosets and mice were harvested for the analysis of lipidomics.

Results

Compared to the control group, we found that phosphatidylethanolamine (PE) (18:0/22:5), PE (16:0/22:5), PE (18:2/22:5), PE (14:0/22:5), and PE (18:1/22:5) increased in the prefrontal cortex of marmosets in the sevoflurane group, while triglyceride (TAG)56:5-fatty acid (FA) 20:4, TAG58:10-FA22:6, and TAG60:10-FA22:6 decreased. For aged mice, we indicated that lipid components phosphatidic acid (PA) (18:1/20:2) and TAG52:5-FA20:4 in the sevoflurane group increased, but PE (14:0/22:4), diglyceride (DAG) (16:1/18:2), and lysophosphatidylcholine (LPC) (16:1) + AcO decreased. More deeply, sevoflurane anesthesia resulted in the presence of 70 specific lipids in mice and marmosets. The enriched lipid subclasses were mainly monoacylglycerophosphoethanolamines and five other subclasses.

Conclusion

Sevoflurane caused slight changes in lipid metabolism both in the aged brain of marmosets and mice. However, the pathways of lipid metabolism were not affected. The effects of sevoflurane on lipid metabolism in aged brains may differ among species.

Alteration of lipid bilayer mechanics by volatile anesthetics: Insights from μs-long molecular dynamics simulations

Very few drugs in clinical practice feature the chemical diversity, narrow therapeutic window, unique route of administration, and reversible cognitive effects of volatile anesthetics. The correlation between their hydrophobicity and their potency and the increasing amount of evidence suggesting that anesthetics exert their action on transmembrane proteins, justifies the investigation of their effects on phospholipid bilayers at the molecular level, given the strong functional and structural link between transmembrane proteins and the surrounding lipid matrix. Molecular dynamics simulations of a model lipid bilayer in the presence of ethylene, desflurane, methoxyflurane, and the nonimmobilizer 1,2-dichlorohexafluorocyclobutane (also called F6 or 2N) at different concentrations highlight the structural consequences of VA partitioning in the lipid phase, with a decrease of lipid order and bilayer thickness, an increase in overall lipid lateral mobility and area-per-lipid, and a marked reduction in the mechanical stiffness of the membrane, that strongly correlates with the compounds' hydrophobicity.

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Molecular simulations of lipid bilayer interaction with volatile anesthetics

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Comparison of volatile anesthetics' and nonimmobilizers' effects on lipid bilayers

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Ligand-dependent partitioning of the compounds in the lipid phase

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Effects on bilayer thickness, stiffness, and lipid order upon ligand partitioning

Allosteric Modulators of G Protein-Coupled Dopamine and Serotonin Receptors: A New Class of Atypical Antipsychotics

Schizophrenia was first described by Emil Krapelin in the 19th century as one of the major mental illnesses causing disability worldwide. Since the introduction of chlorpromazine in 1952, strategies aimed at modifying the activity of dopamine receptors have played a major role for the treatment of schizophrenia. The introduction of atypical antipsychotics with clozapine broadened the range of potential targets for the treatment of this psychiatric disease, as they also modify the activity of the serotoninergic receptors. Interestingly, all marketed drugs for schizophrenia bind to the orthosteric binding pocket of the receptor as competitive antagonists or partial agonists. In recent years, a strong effort to develop allosteric modulators as potential therapeutic agents for schizophrenia was made, mainly for the several advantages in their use. In particular, the allosteric binding sites are topographically distinct from the orthosteric pockets, and thus drugs targeting these sites have a higher degree of receptor subunit specificity. Moreover, “pure” allosteric modulators maintain the temporal and spatial fidelity of native orthosteric ligand. Furthermore, allosteric modulators have a “ceiling effect”, and their modulatory effect is saturated above certain concentrations. In this review, we summarize the progresses made in the identification of allosteric drugs for dopamine and serotonin receptors, which could lead to a new generation of atypical antipsychotics with a better profile, especially in terms of reduced side effects.

Studies on the mechanism of general anesthesia

Anesthetics are used every day in thousands of hospitals to induce loss of consciousness, yet scientists and the doctors who administer these compounds lack a molecular understanding for their action. The chemical properties of anesthetics suggest that they could target the plasma membrane. Here the authors show anesthetics directly target a subset of plasma membrane lipids to activate an ion channel in a two-step mechanism. Applying the mechanism, the authors mutate a fruit fly to be less sensitive to anesthetics and convert a nonanesthetic-sensitive channel into a sensitive one. These findings suggest a membrane-mediated mechanism will be an important consideration for other proteins of which direct binding of anesthetic has yet to explain conserved sensitivity to chemically diverse anesthetics.

Inhaled anesthetics are a chemically diverse collection of hydrophobic molecules that robustly activate TWIK-related K⁺ channels (TREK-1) and reversibly induce loss of consciousness. For 100 y, anesthetics were speculated to target cellular membranes, yet no plausible mechanism emerged to explain a membrane effect on ion channels. Here we show that inhaled anesthetics (chloroform and isoflurane) activate TREK-1 through disruption of phospholipase D2 (PLD2) localization to lipid rafts and subsequent production of signaling lipid phosphatidic acid (PA). Catalytically dead PLD2 robustly blocks anesthetic TREK-1 currents in whole-cell patch-clamp recordings. Localization of PLD2 renders the TRAAK channel sensitive, a channel that is otherwise anesthetic insensitive. General anesthetics, such as chloroform, isoflurane, diethyl ether, xenon, and propofol, disrupt lipid rafts and activate PLD2. In the whole brain of flies, anesthesia disrupts rafts and PLD^null flies resist anesthesia. Our results establish a membrane-mediated target of inhaled anesthesia and suggest PA helps set thresholds of anesthetic sensitivity in vivo.

Anaesthesia with diethyl ether impairs jasmonate signalling in the carnivorous plant Venus flytrap (Dionaea muscipula)

BACKGROUND AND AIMS

General anaesthetics are compounds that induce loss of responsiveness to environmental stimuli in animals and humans. The primary site of action of general anaesthetics is the nervous system, where anaesthetics inhibit neuronal transmission. Although plants do not have neurons, they generate electrical signals in response to biotic and abiotic stresses. Here, we investigated the effect of the general volatile anaesthetic diethyl ether on the ability to sense potential prey or herbivore attacks in the carnivorous plant Venus flytrap (Dionaea muscipula).

METHODS

We monitored trap movement, electrical signalling, phytohormone accumulation and gene expression in response to the mechanical stimulation of trigger hairs and wounding under diethyl ether treatment.

KEY RESULTS

Diethyl ether completely inhibited the generation of action potentials and trap closing reactions, which were easily and rapidly restored when the anaesthetic was removed. Diethyl ether also inhibited the later response: jasmonic acid (JA) accumulation and expression of JA-responsive genes (cysteine protease dionain and type I chitinase). However, external application of JA bypassed the inhibited action potentials and restored gene expression under diethyl ether anaesthesia, indicating that downstream reactions from JA are not inhibited.

CONCLUSIONS

The Venus flytrap cannot sense prey or a herbivore attack under diethyl ether treatment caused by inhibited action potentials, and the JA signalling pathway as a consequence.

Anti-angiogenesis therapy and gap junction inhibition reduce MDA-MB-231 breast cancer cell invasion and metastasis in vitro and in vivo

Cancer cells secrete VEGF, which plays a key role in their growth, invasion, extravasation and metastasis. Direct cancer cell-endothelial cell interaction, mediated by gap junctions, is of critical importance in the extravasation process. In this study, we evaluated avastin (Av), an anti-VEGF antibody; and oleamide (OL), a gap junction inhibitor, using MDA-MB-231 human breast cancer cells in vitro and a xenograft murine model in vivo. Results showed that Av/OL significantly decreased proliferation, induced cell cycle arrest and decreased migration and invasion of MDA-MB-231 cells in vitro. In addition, Av/OL significantly decreased homo and hetero-cellular communication interaction between MDA-MDA and MDA-endothelial cells, respectively. The expression levels of several factors including VEGF, HIF1α, CXCR4, Cx26, Cx43, and MMP9 were attenuated upon Av/OL treatment in vitro. On the other hand, avastin, but not oleamide, reduced tumor size of NSG mice injected subdermally (s.d.) with MDA-MB-231 cells, which was also associated with increased survival. Furthermore, Av but also OL, separately, significantly increased the survival rate, and reduced pulmonary and hepatic metastatic foci, of intravenously (i.v.) injected mice. Finally, OL reduced MMP9 protein expression levels, better than Av and in comparisons to control, in the lungs of MDA-MB-231 i.v. injected NSG mice. In conclusion, while avastin has anti-angiogenic, anti-tumor and anti-metastatic activities, oleamide has anti-metastatic activity, presumably at the extravasation level, providing further evidence for the role of gap junction intercellular communication (GJIC) in cancer cell extravasation.

Modulation of vigilance in the primary hypersomnias by endogenous enhancement of GABAA receptors

The biology underlying excessive daytime sleepiness (hypersomnolence) is incompletely understood. After excluding known causes of sleepiness in 32 hypersomnolent patients, we showed that, in the presence of 10 μM γ-aminobutyric acid (GABA), cerebrospinal fluid (CSF) from these subjects stimulated GABA(A) receptor function in vitro by 84.0 ± 40.7% (SD) relative to the 35.8 ± 7.5% (SD) stimulation obtained with CSF from control subjects (Student's t test, t = 6.47, P < 0.0001); CSF alone had no effect on GABA(A) signaling. The bioactive CSF component had a mass of 500 to 3000 daltons and was neutralized by trypsin. Enhancement was greater for α2 subunit- versus α1 subunit-containing GABA(A) receptors and negligible for α4 subunit-containing ones. CSF samples from hypersomnolent patients also modestly enhanced benzodiazepine (BZD)-insensitive GABA(A) receptors and did not competitively displace BZDs from human brain tissue. Flumazenil--a drug that is generally believed to antagonize the sedative-hypnotic actions of BZDs only at the classical BZD-binding domain in GABA(A) receptors and to lack intrinsic activity--nevertheless reversed enhancement of GABA(A) signaling by hypersomnolent CSF in vitro. Furthermore, flumazenil normalized vigilance in seven hypersomnolent patients. We conclude that a naturally occurring substance in CSF augments inhibitory GABA signaling, thus revealing a new pathophysiology associated with excessive daytime sleepiness.

Effects of isoflurane, halothane, and chloroform on the interactions and lateral organization of lipids in the liquid-ordered phase

The first quantitative insight has been obtained into the effects that volatile anesthetics have on the interactions and lateral organization of lipids in model membranes that mimic "lipid rafts". Specifically, nearest-neighbor recogntion measurements, in combination with Monte Carlo simulations, have been used to investigate the action of isoflurane, halothane, and chloroform on the compactness and lateral organization of cholesterol-rich bilayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in the liquid-ordered (l(o)) phase. All three anesthetics induce a similar weakening of sterol-phospholipid association, corresponding to ca. 30 cal/mol of lipid at clinically relevant concentrations. Monte Carlo lattice simulations show that the lateral organization of the l(o) phase, under such conditions, remains virtually unchanged. In sharp contrast to their action on the l(o) phase, these anesthetics have been found to have a similar strengthening effect on sterol-phospholipid association in the liquid-disordered (l(d)) phase. The possibility of discrete complexes being formed between DPPC and these anesthetics and the biological relevance of these findings are discussed.

Phospholipid complexation of general anesthetics in fluid bilayers

A nearest-neighbor recognition analysis has been performed in cholesterol-rich and cholesterol-poor liposomes derived from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in the presence of varying concentrations of chloroform. This analysis has yielded a fundamentally new, molecular-level view of the interaction of general anesthetics with lipid bilayers, which may be relevant to their biological action; that is, DPPC forms 1:1 complexes with CHCl(3) in both membranes in the fluid bilayer state.

Ethanol/naltrexone interactions at the mu-opioid receptor. CLSM/FCS study in live cells

BACKGROUND

Alcoholism is a widespread chronic disorder of complex aetiology with a significant negative impact on the individual and the society. Mechanisms of ethanol action are not sufficiently well understood at the molecular level and the pharmacotherapy of alcoholism is still in its infancy. Our study focuses at the cellular and molecular level on ethanol-induced effects that are mediated through the micro-opioid receptor (MOP) and on the effects of naltrexone, a well-known antagonist at MOP that is used clinically to prevent relapse in alcoholism.

METHODOLOGY/PRINCIPAL FINDINGS

Advanced fluorescence imaging by Confocal Laser Scanning Microscopy (CLSM) and Fluorescence Correlation Spectroscopy (FCS) are used to study ethanol effects on MOP and plasma membrane lipid dynamics in live PC12 cells. We observed that relevant concentrations of ethanol (10-40 mM) alter MOP mobility and surface density, and affect the dynamics of plasma membrane lipids. Compared to the action of specific ligands at MOP, ethanol-induced effects show complex kinetics and point to a biphasic underlying mechanism. Pretreatment with naloxone or naltrexone considerably mitigates the effects of ethanol.

CONCLUSIONS/SIGNIFICANCE

We suggest that ethanol acts by affecting the sorting of MOP at the plasma membrane of PC12 cells. Naltrexone exerts opposite effects on MOP sorting at the plasma membrane, thereby countering the effects of ethanol. Our experimental findings give new insight on MOP-mediated ethanol action at the cellular and molecular level. We suggest a new hypothesis to explain the well established ethanol-induced increase in the activity of the endogenous opioid system.

IBMX-elicited inhibition of water permeability in the isolated rabbit conjunctival epithelium

Agents expected to increase intracellular cAMP levels were tested on the diffusional water permeability (P(dw)) of isolated rabbit conjunctival epithelia given recent indications of the apical expression of AQP5, a water channel homologue regulated by cAMP in other cell systems. For these experiments, segments of conjunctivae were mounted between Ussing-type hemichambers under short-circuit conditions. Unidirectional water fluxes (J(dw)) were measured by adding (3)H(2)O to one hemichamber and sampling from the other, while the electrical parameters (I(sc) and R(t)) were recorded simultaneously. J(dw) were determined under control conditions and after the introduction of forskolin, dibutyryl-cAMP, rolipram and IBMX. All agents reduced J(dw), with rolipram and IBMX the most effective inhibitors (~28% reduction), while simultaneously evoking stimulations of the I(sc); suggesting that cAMP regulates ionic transport and P(dw) independently. This observation was consistent with the elimination of the IBMX-elicited I(sc) stimulations by the PKA inhibitor, H89, and the ineffectiveness of the sulfonamide in preventing the J(dw) reductions produced by the xanthine. Data from mannitol fluxes and Arrhenius plots indicated that the IBMX-elicited P(dw) reduction occurred at the level of water-transporting channels, but the specific moiety was not identified. Instead it was observed that lipophiles commonly used in other systems to uncouple cellular communication precluded the effects of IBMX on J(dw), but the mechanism for these results was not directly linked to gap-junction blockade in the conjunctiva, as assessed by the transepithelial electrical parameters. Putatively, agents such as heptanol, by also fluidizing the bilayer, may have changed the conformation of a water channel in a manner preventing down-regulation by IBMX. Nevertheless, this study uncovered an apparently unique response to cAMP elevation exhibited by the conjunctiva, namely that P(dw) declines via an H89-insensitive pathway under conditions whereby PKA-dependent electrolyte transport might be over stimulated due to excessive cAMP levels (e.g., PDE inhibition).

Enhanced radiosensitization of p53 mutant cells by oleamide

PURPOSE

Effect of oleamide, an endogenous fatty-acid primary amide, on tumor cells exposed to ionizing radiation (IR) has never before been explored.

METHODS AND MATERIALS

NCI H460, human lung cancer cells, and human astrocytoma cell lines, U87 and U251, were used. The cytotoxicity of oleamide alone or in combination with IR was determined by clonogenic survival assay, and induction of apoptosis was estimated by FACS analysis. Protein expressions were confirmed by Western blotting, and immunofluorescence analysis of Bax by use of confocal microscopy was also performed. The combined effect of IR and oleamide to suppress tumor growth was studied by use of xenografts in the thighs of nude mice.

RESULTS

Oleamide in combination with IR had a synergistic effect that decreased clonogenic survival of lung-carcinoma cell lines and also sensitized xenografts in nude mice. Enhanced induction of apoptosis of the cells by the combined treatment was mediated by loss of mitochondrial membrane potential, which resulted in the activation of caspase-8, caspase-9, and caspase-3 accompanied by cytochrome c release and Bid cleavage. The synergistic effects of the combined treatment were more enhanced in p53 mutant cells than in p53 wild-type cells. In p53 wild-type cells, both oleamide and radiation induced Bax translocation to mitochondria. On the other hand, in p53 mutant cells, radiation alone slightly induced Bax translocation to mitochondria, whereas oleamide induced a larger translocation.

CONCLUSIONS

Oleamide may exhibit synergistic radiosensitization in p53 mutant cells through p53-independent Bax translocation to mitochondria.

Dicumarol is a potent reversible inhibitor of gap junctional intercellular communication

Dicumarol [3,3'-methylene-bis(4-hydroxycoumarin)] is a potent inhibitor of NAD(P)H:quinone oxidoreductase-1. Exposure of rat liver epithelial cells or of human skin fibroblasts to dicumarol resulted in a rapid and complete inhibition of connexin-43-dependent gap junctional intercellular communication (GJC). GJC was restored within 60min following removal of dicumarol. The concentration of dicumarol required for half maximal inhibition of GJC was 3muM, making dicumarol about 10-fold more effective in blocking GJC than 1-octanol and flufenamic acid, known inhibitors of GJC. Warfarin, a related coumarin derivative, also attenuated GJC, yet very high concentrations of 5-10mM were required. Dicumarol-induced downregulation of GJC was found not to be due to an interference with pathways enhancing the phosphorylation of connexin-43, such as epidermal growth factor receptor and extracellular signal-regulated kinase pathways. Rather, inhibition of GJC by dicumarol was paralleled by a reversible loss of a phosphorylated form ("P2") of connexin-43.

Cholestatic bile acids inhibit gap junction permeability in rat hepatocyte couplets and normal rat cholangiocytes

BACKGROUND/AIMS

The aim of this work was to study the effects of different bile acids on the permeability of gap junction channels (PGJC). We also looked at the effects of some bile acids on the coordination of intercellular calcium oscillations.

METHODS

The permeability of gap junctions was assessed by fluorescent dye transfer and calcium signalling on fluorescent microscopy.

RESULTS

Cholestatic bile acids such as taurolithocholate, taurolithocholate-sulfate and taurochenodeoxycholate inhibit the permeability of gap junctions in a dose-dependent and reversible manner in hepatocytes. Experiments performed in other cell types suggest that this effect is specific for cells having bile salt transporters, independently of the type of connexin expressed in these cells. Thus, cholestatic bile acids inhibit PGJC in normal rat cholangiocytes which express Cx43, but not in HeLa cells transfected with Cx26 or 32, which are expressed in hepatocytes. Calcium oscillations induced by bile acids in rat hepatocyte couplets are not coordinated and, by inhibiting the PGJC, cholestatic bile acids prevent the coordination of calcium oscillations induced by noradrenaline in these cells.

CONCLUSIONS

Cholestatic, but not choleretic bile acids inhibit the PGJC in cells able to accumulate bile acids. This inhibition might contribute to the cholestatic effect of these bile acids.

Selective effect of oleamide, an endogenous sleep-inducing lipid amide, on pentylenetetrazole-induced seizures in mice

The anti-seizure effect of oleamide, an endogenous sleep-inducing fatty acid amide, was studied in mice. Oleamide, in the dose range 43.7-700.0 mg kg(-1), significantly and dose-dependently inhibited the seizures induced by pentylenetetrazole. However, oleamide showed no inhibitory action on the seizures induced by picrotoxin, strychnine, caffeine or semicarbazide. These results provide the first evidence for the anti-seizure effect of oleamide, and suggest that this effect may be selective to the seizure model induced by pentylenetetrazole.

Large-scale molecular dynamics simulations of general anesthetic effects on the ion channel in the fully hydrated membrane: the implication of molecular mechanisms of general anesthesia

Interactions of volatile anesthetics with the central nervous system are characterized by low yet specific binding affinities. Although neurotransmitter-gated ion channels are considered the primary anesthetic targets, the mechanism of action at the molecular level remains elusive. We consider here the theoretical implications of channel dynamics on anesthetic action in a simplified membrane-channel system. Large-scale 2.2-ns all-atom molecular dynamics simulations were performed to study the effects of halothane, a clinical anesthetic, on a gramicidin A (gA) channel in a fully hydrated dimyristoyl phosphatidylcholine membrane. In agreement with experimental results, anesthetics preferentially target the anchoring residues at the channel-lipid-water interface. Although the anesthetic effect on channel structure is minimal, the presence of halothane profoundly affects channel dynamics. For 2.2-ns simulation, the rms fluctuation of gA backbone in the lipid core increases from approximately equal 1 A in the absence of anesthetics to approximately equal 1.5 A in the presence of halothane. Autocorrelation analysis reveals that halothane (i) has no effect on the subpicosecond librational motion, (ii) prolongs the backbone autocorrelation time in the 10- to 100-ps time scale, and (iii) significantly decreases the asymptotic values of generalized order parameter and correlation time of nanosecond motions for the inner but not the outer residues. The simulation results discount the viewpoint of a structure-function paradigm that overrates the importance of structural fitting between general anesthetics and yet-unidentified hydrophobic protein pockets. Instead, the results underscore the global, as opposed to local, effects of anesthetics on protein dynamics as the underlying mechanisms for the action of general anesthetics and possibly of other low-affinity drugs.

The endocannabinoid system: function in survival of the embryo, the newborn and the neuron

Since the identification and cloning of the first cannabinoid (CB1) receptor and the subsequent discovery of the endogenous cannabinoid ligands (endocannabinoids), anandamide, 2-arachidonoyl glycerol (2-AG) and noladin ether, a intensive search for their function in health and disease has been launched. The endocannabinoids in the central nervous system bind Gi/o coupled CB1 receptors that modulate adenylyl cyclase, ion channels and extracellular signal-regulated kinases. The present review discusses the nature of endocannabinoid (anandamide and 2-AG) neurotransmission, the activity of cannabinoids and the possibility that some of these activities are mediated via a receptor, yet to be discovered, which is distinct from the brain specific CB1 receptor. Three physiological functions in which the endocannabinoids play a critical role are also discussed: embryonal implantation, feeding and appetite, and neuroprotection.

Oleamide attenuates apoptotic death in cultured rat cerebellar granule neurons

The effect of oleamide on apoptosis was investigated by using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay, DNA staining assay with propidium iodide and caspase-3 activity analyses. The present results showed that oleamide significantly attenuated the cell death and nuclear condensation of cultured rat cerebellar granule neurons induced by K(+) deprivation in a dose-dependent manner. The oleamide actions were well parallel with the attenuation of caspase-3 activity in the process of apoptotic death. Moreover, neither elaidic acid nor stearic acid, two fatty acids structurally related to oleamide without the Delta(9)-cis double bond, had similar effects on the cell death, suggesting the selectively structural features of oleamide required for this action. These data provided the first evidence of a protective effect of oleamide against apoptosis in a structurally specific manner.

The sleep hormone oleamide modulates inhibitory ionotropic receptors in mammalian CNS in vitro

1. We examine the sensitivity of GABA(A) and glycine receptors (same ionotropic superfamily) to oleamide. We address subunit-dependence/modulatory mechanisms and analogies with depressant drugs. 2. Oleamide modulated human GABA(A) currents (alpha(1)beta(2)gamma(2L)) in oocytes (EC(50), 28.94+/-s.e.mean of 1.4 microM; Maximum 216%+/-35 of control, n=4). Modulation of human alpha1 glycine homo-oligomers (significant), was less marked, with a lower EC(50) (P<0.05) than GABA receptors (EC(50), 22.12+/-1.4 microM; Maximum 171%+/-30, n=11). 3. Only the hypnogenic cis geometric isomer enhanced glycine currents (without altering slope or maximal current, it reduced the glycine EC(50) from 322 to 239 microM: P<0.001). Modulation was not voltage-dependent or associated with a shift in E(r). 4. beta 1 containing GABA(A) receptors (insensitive to many depressant drugs) were positively modulated by oleamide. Oleamide efficacy was circa 2x greater at alpha(1)beta(1)gamma(2L) than alpha(1)beta(2)gamma(2L) (P=0.007). Splice variation in gamma subunits did not alter oleamide sensitivity. 5. cis-9,10-Octadecenoamide had no effect on the equilibrium binding of [(3)H]-muscimol or [(3)H]-EBOB to mouse brain membranes. It does not directly mimic GABA, or operate as a neurosteroid-, benzodiazepine- or barbiturate-like modulator of GABA(A)-receptors. 6. The transport of [(3)H]-GABA into mouse brain synaptoneurosomes was unaffected by high micromolar concentrations of cis-9,10-octadecenoamide. Oleamide does not enhance GABA-ergic currents or prolong IPSCs by inhibiting GABA transport. 7. Oleamide is a non-selective modulator of inhibitory ionotropic receptors. The sleep lipid exerts its effects indirectly, or at a novel recognition site on the GABA(A) complex.

Endocannabinoids in the central nervous system--an overview

Many aspects of the physiology and pharmacology of anandamide (arachidonoyl ethanol amide), the first endogenous cannabinoid ligand ("endocannabinoid") isolated from pig brain, have been studied since its discovery in 1992. Ethanol amides from other fatty acids have also been identified as endocannabinoids with similar in vivo and in vitro pharmacological properties. 2-Arachidonoyl glycerol and noladin ether (2-arachidonyl glyceryl ether), isolated in 1995 and 2001, respectively, so far, display pharmacological properties in the central nervous system, similar to those of anandamide. The endocannabinoids are widely distributed in brain, they are synthesized and released upon neuronal stimulation, undergo reuptake and are hydrolyzed intracellularly by fatty acid amide hydrolase (FAAH). For therapeutic purposes, inhibitors of FAAH may provide more specific cannabinoid activities than direct agonists, and several such molecules have already been developed. Pharmacological effects of the endocannabinoids are very similar, yet not identical, to those of the plant-derived and synthetic cannabinoid receptor ligands. In addition to pharmacokinetic explanations, direct or indirect interactions with other receptors have been considered to explain some of these differences, including activities at serotonin and GABA receptors. Binding affinities for other receptors such as the vanilloid receptor, have to be taken into account in order to fully understand endocannabinoid physiology. Moreover, possible interactions with receptors for the lysophosphatidic acids deserve attention in future studies. Endocannabinoids have been implicated in a variety of physiological functions. The areas of central activities include pain reduction, motor regulation, learning/memory, and reward. Finally, the role of the endocannabinoid system in appetite stimulation in the adult organism, and perhaps more importantly, its critical involvement in milk ingestion and survival of the newborn, may not only further our understanding of the physiology of food intake and growth, but may also find therapeutic applications in wasting disease and infant's "failure to thrive".

Mechanism of anesthetic action: oxygen pathway perturbation hypothesis

Although more than 150 years have passed since the discovery of general anesthetics, precisely how they work remains a mystery. We propose a novel unitary mechanism of general anesthesia verifiable by experiments. In the proposed mechanism, general anesthetics perturb oxygen pathways in both membranes and oxygen-utilizing proteins, such that the availability of oxygen to its sites of utilization is reduced, which in turn triggers cascading cellular responses through oxygen-sensing mechanisms, resulting in general anesthesia. Despite the general assumption that cell membranes are readily permeable to oxygen, existing publications indicate that these membranes are plausible oxygen-transport barriers. The present hypothesis provides a unified framework for explaining phenomena associated with general anesthesia and experimental results on the actions of general anesthetics. If verified by experiments, the proposed mechanism also has other significant medical and biological implications.

Induction of peptidylglycine alpha-amidating monooxygenase in N(18)TG(2) cells: a model for studying oleamide biosynthesis

The fatty-acid primary amide, oleamide, is a novel signaling molecule whose mechanism of biosynthesis is unknown. Recently, the N(18)TG(2) cell line was shown to synthesize oleamide from oleic acid, thereby demonstrating that these cells contain the necessary catalytic activities for generating the fatty-acid primary amide. The ability of peptide alpha-amidating enzyme, peptidylglycine-alpha-amidating monooxygenase (PAM; EC 1.14.17.3), to catalyze the formation of oleamide from oleoylglycine in vitro suggests this as a function for the enzyme in vivo. This investigation shows that N(18)TG(2) cells, in fact, express PAM and that cellular differentiation dramatically increases this expression. PAM expression was confirmed by the detection of PAM mRNA, PAM protein, and enzymatic activity that exhibits the functional characteristics of PAM isolated from mammalian neuroendocrine tissues. The regulated expression of PAM in N(18)TG(2) cells is consistent with the proposed role of PAM in the biosynthesis of fatty-acid primary amides and further establishes this cell line as a model for studying the pathway.

Oleamide-mediated sleep induction does not depend on perturbation of membrane homeoviscosity

To verify whether the sleep-inducing properties of oleamide were related to its ability to perturb membrane homeoviscosity, affecting 5-HT(2A) receptors, we compared the effects of oleamide and oleic acid, the latter lacking both the sleep-inducing effect and the action on 5-HT(2A) receptors. In binding studies the two compounds did not directly interact with rat brain cortex 5-HT(2A) receptors, nor did they increase the affinity of a 5-HT(2A) agonist, either in vitro or ex vivo. They had similar fluidizing effects, in vitro at high concentrations (>/=10 microM), and ex vivo after a dose of 100 mg/kg, and they reduced locomotor activity with similar potency. There thus appears to be no causal relationship between the fluidizing effects of oleamide and its sleep-inducing properties.

Mass spectrometry of the intramolecular nitrogen isotope distribution of environmental nitrous oxide using fragment-ion analysis

Mass spectrometry is applied to measure the intramolecular distribution of (15)N in N(2)O samples of near natural isotopic composition. The method is relatively straightforward and based on the analysis of the (14)NO and (15)NO fragment ion beams at mass 30 and 31, respectively, in combination with the standard analysis of the masses 44, 45, and 46 of the non-fragmented N(2)O. Various complications in the application, not all of which are resolved at present, are discussed. Copyright 1999 John Wiley & Sons, Ltd.

Endocannabinoids

The background knowledge leading to the isolation and identification of anandamide and 2-arachidonoyl glycerol, the principal endocannabinoids is described. The structure-activity relationships of these lipid derivatives are summarized. Selected biochemical and pharmacological topics in this field are discussed, the main ones being levels of endocannabinoids in unstimulated tissue and cells, biosynthesis, release and inactivation of endocannabinoids, the effects of 'entourage' compounds on the activities of anandamide and 2-arachidonoyl glycerol, their signaling mechanisms and effects in animals.

Chemical requirements for inhibition of gap junction communication by the biologically active lipid oleamide

Oleamide is an endogenous fatty acid primary amide that possesses sleep-inducing properties in animals and has been shown to effect serotonergic systems and block gap junction communication in a structurally specific manner. Herein, the structural features of oleamide required for inhibition of the gap junction-mediated chemical and electrical transmission in rat glial cells are defined. The effective inhibitors fall into two classes of fatty acid primary amides of which oleamide and arachidonamide are the prototypical members. Of these two, oleamide constitutes the most effective, and its structural requirements for inhibition of the gap junction are well defined. It requires a chain length of 16-24 carbons of which 16-18 carbons appears optimal, a polarized terminal carbonyl group capable of accepting but not necessarily donating a hydrogen bond, a Delta9 cis double bond, and a hydrophobic methyl terminus. Within these constraints, a range of modifications are possible, many of which may be expected to improve in vivo properties. A select set of agents has been identified that serves both as oleamide agonists and as inhibitors of fatty acid amide hydrolase, which is responsible for the rapid inactivation of oleamide.

Structural requirements for 5-HT2A and 5-HT1A serotonin receptor potentiation by the biologically active lipid oleamide

Oleamide is an endogenous fatty acid primary amide that possesses sleep-inducing properties in animals and that has been shown to effect serotonergic receptor responses and block gap junction communication. Herein, the potentiation of the 5-HT1A receptor response is disclosed, and a study of the structural features of oleamide required for potentiation of the 5-HT2A and 5-HT1A response to serotonin (5-HT) is described. Of the naturally occurring fatty acids, the primary amide of oleic acid (oleamide) is the most effective at potentiating the 5-HT2A receptor response. The structural features required for activity were found to be highly selective. The presence, position, and stereochemistry of the delta9-cis double bond is required, and even subtle structural variations reduce or eliminate activity. Secondary or tertiary amides may replace the primary amide but follow a well defined relationship requiring small amide substituents, suggesting that the carboxamide serves as a hydrogen bond acceptor but not donor. Alternative modifications at the carboxamide as well as modifications of the methyl terminus or the hydrocarbon region spanning the carboxamide and double bond typically eliminate activity. A less extensive study of the 5-HT1A potentiation revealed that it is more tolerant and accommodates a wider range of structural modifications. An interesting set of analogs was identified that inhibit rather than potentiate the 5-HT2A, but not the 5-HT1A, receptor response, further suggesting that such analogs may permit the selective modulation of serotonin receptor subtypes and even have opposing effects on the different subtypes.