Isovaleric, methylmalonic, and propionic acid decrease anesthetic EC50 in tadpoles, modulate glycine receptor function, and interact with the lipid 1,2-dipalmitoyl-Sn-glycero-3-phosphocholine

Kinetic Model of Adsorption of Aqueous Solutes onto Lipid Bilayers: Modulation of the Activity of Membrane Proteins

It has been argued that membrane proteins that are activated by agonist binding and whose activity depends on conformational transitions are sensitive to membrane adsorption of agonists as well as other solutes such as anesthetics. Ligand-gated ion channels such as GABA_AR have been observed electrophysiologically to exhibit remarkable temporal complexity, with multiple time scales of desensitization and deactivation that depend on concentration over a very broad range. Earlier theoretical work was able to predict much of this complexity for GABA_AR using a model that incorporates a simple Langmuir approximation of adsorption and desorption of neurotransmitters and solutes such as anesthetics, along with classical modeling of ligand binding and conformational transitions among the three canonical protein states. Here, a simple kinetic model is developed that improves on the Langmuir approach by incorporating the energetics of adsorbate-adsorbate (and adsorbate-bilayer) interactions. Predicted equilibrium isotherms are compared to experimental results, along with the time-course of adsorption/desorption, over a range of values of energetic parameters. Initial predictions of effects of adsorbate energetics on ion current traces involving long and short pulses of agonists show remarkably large effects on the time scale(s) of desensitization and deactivation.

Anesthetic Pharmacology of the Mint Extracts L-Carvone and Methyl Salicylate

INTRODUCTION

Hydrocarbons with sufficient water solubility allosterically modulate anesthetic-sensitive ion channels. Mint extracts L-carvone and methyl salicylate water solubility exceeds modulation cutoff values for γ-amino butyric acid type A (GABAA) receptors, N-methyl-D-aspartate (NMDA) receptors, and type-2 voltage-gated sodium (Nav1.2) channels. We hypothesized that mint extracts modulate these channels at concentrations that anesthetize rats.

METHODS

Channels were expressed separately in frog oocytes and studied using 2-electrode voltage clamp techniques at drug concentrations up to 10 mM. Normalized current effects were fit to Hill equations. Mint compounds were formulated in a lipid emulsion and administered IV to rats. When unresponsive to the tail clamp, rats were exsanguinated, and plasma drug concentrations were measured.

RESULTS

Both mint compounds caused concentration-dependent inhibition of all channels except for methyl salicylate which inhibited GABAA receptors at low concentrations and potentiated at high concentrations. Plasma drug concentrations in anesthetized rats were 7.9 mM for L-carvone and 2.7 mM for methyl salicylate. This corresponded to ≥53% NMDA receptor inhibition and ≥78% Nav1.2 channel inhibition by both compounds and 30% potentiation of GABAA receptors by methyl salicylate.

CONCLUSION

L-Carvone and methyl salicylate allosterically modulate cell receptor targets important to molecular actions of conventional anesthetics at concentrations that also induce general anesthesia in rats.

Dietary Fatty Acids and Microbiota-Brain Communication in Neuropsychiatric Diseases

The gut-brain axis is a multimodal communication system along which immune, metabolic, autonomic, endocrine and enteric nervous signals can shape host physiology and determine liability, development and progression of a vast number of human diseases. Here, we broadly discussed the current knowledge about the either beneficial or deleterious impact of dietary fatty acids on microbiota-brain communication (MBC), and the multiple mechanisms by which different types of lipids can modify gut microbial ecosystem and contribute to the pathophysiology of major neuropsychiatric diseases (NPDs), such as schizophrenia (SCZ), depression and autism spectrum disorders (ASD).

An Akkermansia muciniphila subtype alleviates high-fat diet-induced metabolic disorders and inhibits the neurodegenerative process in mice

The prevalence of obesity and diabetes, and their complicating mental disorders, severely affect public health. This study aimed to investigate the long-term effects of an Akkermansia muciniphila subtype (A. muciniphila^sub) on high-fat diet-induced obesity and diabetes, and to evaluate whether this subtype can alleviate their complicated mental disorders. Whole genome sequencing and short chain fatty acid production analysis in supernatant of pure culture were performed. Female adult C57BL/6 mice were fed a high-fat diet or a normal chow diet and were gavaged with A. muciniphila^sub or phosphate-buffered saline daily for 10 months. Body weight, food consumption and blood glucose were measured. At the end of the treatment period, all mice were subjected to the Y-maze test, sucrose preference test, analyses of serum, fecal microbiota analysis and histological examination. This A. muciniphila^sub had 278 unique genes compared to the type strain (A. muciniphila ATCC BAA-835) and produced short chain fatty acids both. A. muciniphila^sub administration significantly reduced body weight gain and improved the spatial memory of high-fat diet-fed mice. A. muciniphila^sub increased Nissl bodies in neurons of the hippocampus, and restored the high-fat diet-inhibited tryptophan metabolism. The high-fat diet led to decreased serum 5-hydroxytryptamine and induced depression, which were not alleviated by A. muciniphila^sub. A. muciniphila^sub increased the relative fecal abundance of Bifidobacterium, and was negatively correlated with the fecal abundance of Bacteroides. The present study demonstrated the beneficial effects of this A. muciniphila^sub on body weight, blood glucose control and the alleviation of the memory decay caused by a high-fat diet in mice.

Understanding of anesthesia - Why consciousness is essential for life and not based on genes

Anesthesia and consciousness represent 2 mysteries not only for biology but also for physics and philosophy. Although anesthesia was introduced to medicine more than 160 y ago, our understanding of how it works still remains a mystery. The most prevalent view is that the human brain and its neurons are necessary to impose the effects of anesthetics. However, the fact is that all life can be anesthesized. Numerous theories have been generated trying to explain the major impact of anesthetics on our human-specific consciousness; switching it off so rapidly, but no single theory resolves this enduring mystery. The speed of anesthetic actions precludes any direct involvement of genes. Lipid bilayers, cellular membranes, and critical proteins emerge as the most probable primary targets of anesthetics. Recent findings suggest, rather surprisingly, that physical forces underlie both the anesthetic actions on living organisms as well as on consciousness in general.

Valerian inhibits rat hepatocarcinogenesis by activating GABA(A) receptor-mediated signaling

Valerian is widely used as a traditional medicine to improve the quality of sleep due to interaction of several active components with the γ-aminobutyric acid (GABA) A receptor (GABA(A)R) system. Recently, activation of GABA signaling in stem cells has been reported to suppress cell cycle progression in vivo. Furthermore, possible inhibitory effects of GABA(A)R agonists on hepatocarcinogenesis have been reported. The present study was performed to investigate modulating effects of Valerian on hepatocarcinogenesis using a medium-term rat liver bioassay. Male F344 rats were treated with one of the most powerful Valerian species (Valeriana sitchensis) at doses of 0, 50, 500 and 5000 ppm in their drinking water after initiation of hepatocarcinogenesis with diethylnitrosamine (DEN). Formation of glutathione S-transferase placental form positive (GST-P⁺) foci was significantly inhibited by Valerian at all applied doses compared with DEN initiation control rats. Generation of 8-hydroxy-2′-deoxyguanosine in the rat liver was significantly suppressed by all doses of Valerian, likely due to suppression of Nrf2, CYP7A1 and induction of catalase expression. Cell proliferation was significantly inhibited, while apoptosis was induced in areas of GST-P⁺ foci of Valerian groups associated with suppression of c-myc, Mafb, cyclin D1 and induction of p21^Waf1/Cip1, p53 and Bax mRNA expression. Interestingly, expression of the GABA(A)R alpha 1 subunit was observed in GST-P⁺ foci of DEN control rats, with significant elevation associated with Valerian treatment. These results indicate that Valerian exhibits inhibitory effects on rat hepatocarcinogenesis by inhibiting oxidative DNA damage, suppressing cell proliferation and inducing apoptosis in GST-P⁺ foci by activating GABA(A)R-mediated signaling.

Molecular mechanisms of drug action: an emerging view

Volatile anesthetics serve as useful probes of a conserved biological process that is essential to the proper functioning of the central nervous system. A kinetic and thermodynamic analysis of their unusual pharmacological and physiological characteristics has led to a general, predictive theory in which small molecules that adsorb to membranes modulate ion channel function by altering physical properties of membrane bilayers. A kinetic model that is both parsimonious and falsifiable has been developed to test this mechanism. This theory leads to predictions about the structure, function, origin, and evolution of synapses, the etiology of several diseases and disease symptoms affecting the brain, and the mechanism of action of several drugs that are used therapeutically. Neuronal membranes may offer an appealing drug target, given the large number of compounds that adsorb to interfaces and hence membranes.

3-Hydroxybutyric acid interacts with lipid monolayers at concentrations that impair consciousness

3-Hydroxybutyric acid (also referred to as β-hydroxybutyric acid or BHB), a small molecule metabolite whose concentration is elevated in type I diabetes and diabetic coma, was found to modulate the properties of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayers when added to the subphase at clinical concentrations. This is a key piece of evidence supporting the hypothesis that the anesthetic actions of BHB are due to the metabolite's abilities to alter physical properties of cell membranes, leading to indirect effects on membrane protein function. Pressure-area isotherms show that BHB changes the compressibility of the monolayer and decrease the size of the two-phase coexistence region. Epi-fluorescent microscopy further reveals that the reduction of the coexistence region is due to the significant reduction in morphology of the liquid condensed domains in the two-phase coexistence region. These changes in monolayer morphology are associated with the diminished interfacial viscosity of the monolayers (measured using an interfacial stress rheometer), which gives insight as to how changes in phase and structure may contribute to membrane function.

Fluorescence anisotropy of diphenylhexatriene and its cationic Trimethylamino derivative in liquid dipalmitoylphosphatidylcholine liposomes: opposing responses to isoflurane

Background

The mechanism of action of volatile general anesthetics has not yet been resolved. In order to identify the effects of isoflurane on the membrane, we measured the steady-state anisotropy of two fluorescent probes that reside at different depths. Incorporation of anesthetic was confirmed by shifting of the main phase transition temperature.

Results

In liquid crystalline dipalmitoylphosphatidylcholine liposomes, isoflurane (7-25 mM in the bath) increases trimethylammonium-diphenylhexatriene fluorescence anisotropy by ~0.02 units and decreases diphenylhexatriene anisotropy by the same amount.

Conclusions

The anisotropy data suggest that isoflurane decreases non-axial dye mobility in the headgroup region, while increasing it in the tail region. We propose that these results reflect changes in the lateral pressure profile of the membrane.