Small intestinal viability assessment using dielectric relaxation spectroscopy and deep learning

Intestinal ischemia is a serious condition where the surgeon often has to make important but difficult decisions regarding resections and resection margins. Previous studies have shown that 3 h (hours) of warm full ischemia of the small bowel followed by reperfusion appears to be the upper limit for viability in the porcine mesenteric ischemia model. However, the critical transition between 3 to 4 h of ischemic injury can be nearly impossible to distinguish intraoperatively based on standard clinical methods. In this study, permittivity data from porcine intestine was used to analyze the characteristics of various degrees of ischemia/reperfusion injury. Our results show that dielectric relaxation spectroscopy can be used to assess intestinal viability. The dielectric constant and conductivity showed clear differences between healthy, ischemic and reperfused intestinal segments. This indicates that dielectric parameters can be used to characterize different intestinal conditions. In addition, machine learning models were employed to classify viable and non-viable segments based on frequency dependent dielectric properties of the intestinal tissue, providing a method for fast and accurate intraoperative surgical decision-making. An average classification accuracy of 98.7% was obtained using only permittivity data measured during ischemia, and 96.2% was obtained with data measured during reperfusion. The proposed approach allows the surgeon to get accurate evaluation from the trained machine learning model by performing one single measurement on an intestinal segment where the viability state is questionable.

Temperature dependence of the microwave dielectric properties of [Formula: see text]-aminobutyric acid

The GABA molecule is the major inhibitory neurotransmitter in the mammalian central nervous system. Through binding to post-synaptic neurons, GABA reduces the neuronal excitability by hyperpolarization. Correct binding between the GABA molecules and its receptors relies on molecular recognition. Earlier studies suggest that recognition is determined by the geometries of the molecule and its receptor. We employed dielectric relaxation spectroscopy (DRS) to study the conformation and dielectric properties of the GABA molecule under physiologically relevant laboratory conditions. The dielectric properties of GABA investigated have given us new insights about the GABA molecule, such as how they interact with each other and with water molecules at different temperatures (22°C and 37.5°C). Higher temperature leads to lower viscosity, thus lower relaxation time. The change in the GABA relaxation time due to concentration change is more associated with the solution viscosity than with the GABA dipole moment. A resonance behavior was observed with high GABA concentrations at physiological temperature, where there might be a phase transition at a certain temperature for a given GABA concentration that leads to a sudden change of the dielectric properties.

On the issue of closed versus open forms of gamma-aminobutyric acid (GABA) in water: Ab initio molecular dynamics and metadynamics studies

Gamma-aminobutyric acid (GABA), a primary neurotransmitter, accomplishes its activities by binding to different receptor sites in different conformations. It is known to have two major conformers: the closed and open forms. Earlier studies on preferred conformation of GABA in water revealed differing results with some reporting the open form while others inferring the closed form to be more stable. We found the existence of many open forms and only one closed form of GABA in water through ab initio metadynamics simulation. Some of the open conformers are equally or more stable while others are less stable than the closed form. Free energy barriers reveal that different conformers are interconvertible at room temperature in typical experimental time scales. Ab initio molecular dynamics simulations are performed to further investigate the inter-conversion of various conformers of GABA in water and their dipole moments and also to make connections to experiments on the conformation of GABA in water.

Docking and pharmacodynamic studies on hGAT1 inhibition activity in the presence of selected neuronal and astrocytic inhibitors. Part I

Inhibition of 4-aminobutanoic acid (GABA) uptake is a strategy for enhancing GABA transmission. The utility of this approach is demonstrated by the successful development of such agents for the treatment of epilepsy and pain. Existing reports on acute brain slice preparations indicate the intersecting of complementary channels and receptors sets between astrocytes and neurons cells. Thorough analysis of astroglial cells by means of molecular and functional studies demonstrated their active modulatory role in intercellular communication. The chemical interactions between sixteen GABA analogues and isoform of hGAT1 is outlined in the light of molecular docking results. In the in vivo part antinociceptive properties of racemic nipecotic acid, its R and S enantiomers and isonipecotic acid, each administered intraperitoneally at 3 fixed doses (10, 30 and 100 mg/kg), were assessed in a thermally-induced acute pain model i.e. the mouse hot plate test. Docking analyses provided complex binding energies, specific h-bond components, and h-bond properties, such as energies, distances and angles. In vivo tests revealed statistically significant antinociceptive properties of isonipecotic acid (10 and 30 mg/kg), R-nipecotic acid (30 and 100 mg/kg) and S-nipecotic acid (100 mg/kg) in mice. The docking data endorse the hypothesis of correlation between the strength of their chemical interactions with hGAT1 and analgesic action of studied compounds.

pH Dependence of γ-Aminobutyric Acid Iontronic Transport

The organic electronic ion pump (OEIP) has been developed as an "iontronic" tool for delivery of biological signaling compounds. OEIPs rely on electrophoretically "pumping" charged compounds, either at neutral or shifted pH, through an ion-selective channel. Significant shifts in pH lead to an abundance of H⁺ or OH^-, which are delivered along with the intended substance. While this method has been used to transport various neurotransmitters, the role of pH has not been explored. Here we present an investigation of the role of pH on OEIP transport efficiency using the neurotransmitter γ-aminobutyric acid (GABA) as the model cationic delivery substance. GABA transport is evaluated at various pHs using electrical and chemical characterization and compared to molecular dynamics simulations, all of which agree that pH 3 is ideal for GABA transport. These results demonstrate a useful method for optimizing transport of other substances and thus broadening OEIP applications.

GABA-ρ receptors: distinctive functions and molecular pharmacology

The homomeric GABA-ρ ligand-gated ion channels (also known as GABA_C or GABA_A -ρ receptors) are similar to heteromeric GABA_A receptors in structure, function and mechanism of action. However, their distinctive pharmacological properties and distribution make them of special interest. This review focuses on GABA-ρ ion channel structure, ligand selectivity toward ρ receptors over heteromeric GABA_A receptor sub-types and selectivity between different homomeric ρ sub-type receptors. Several GABA analogues show selectivity at homomeric GABA-ρ receptors over heteromeric GABA_A receptors. More recently, some synthetic ligands have been found to show selectivity at receptors formed from one ρ subtype over others. The unique pharmacological profiles of these agents are discussed in this review. The classical binding site of GABA within the orthosteric site of GABA-ρ homomeric receptors is discussed in detail regarding the loops and residues that constitute the binding site. The ligand-residue interactions in this classical binding and those of mutant receptors are discussed. The structure and conformations of GABA are discussed in regard to its flexibility and molecular properties. Although the binding mode of GABA is difficult to predict, several interactions between GABA and the receptor assist in predicting its potential conformation and mode of action. The structure-activity relationships of GABA and structurally key ligands at ρ receptors are described and discussed.

Theoretical and experimental NMR studies on muscimol from fly agaric mushroom (Amanita muscaria)

In this article we report results of combined theoretical and experimental NMR studies on muscimol, the bioactive alkaloid from fly agaric mushroom (Amanita muscaria). The assignment of (1)H and (13)C NMR spectra of muscimol in DMSO-d6 was supported by additional two-dimensional heteronuclear correlated spectra (2D NMR) and gauge independent atomic orbital (GIAO) NMR calculations using density functional theory (DFT). The effect of solvent in theoretical calculations was included via polarized continuum model (PCM) and the hybrid three-parameter B3LYP density functional in combination with 6-311++G(3df,2pd) basis set enabled calculation of reliable structures of non-ionized (neutral) molecule and its NH and zwitterionic forms in the gas phase, chloroform, DMSO and water. GIAO NMR calculations, using equilibrium and rovibrationally averaged geometry, at B3LYP/6-31G* and B3LYP/aug-cc-pVTZ-J levels of theory provided muscimol nuclear magnetic shieldings. The theoretical proton and carbon chemical shifts were critically compared with experimental NMR spectra measured in DMSO. Our results provide useful information on its structure in solution. We believe that such data could improve the understanding of basic features of muscimol at atomistic level and provide another tool in studies related to GABA analogs.