Electrophysiological Evidence for Anti-epileptic Property of Taurine.

Taurine, 2-aminoethanesulfonic acid, is one of the most abundant free amino acids especially in excitable tissues, with wide physiological actions. Several lines of evidence suggest that taurine may function as a potent inhibitory neuromodulator that regulate neuronal activity in many cerebral areas. Parenteral injection of kainic acid (KA), a glutamate receptor agonist, causes severe and stereotyped behavioral convulsions in mice and is used as a rodent model for human temporal lobe epilepsy. In the adult brain, inhibitory GABAergic interneurons modulate the activity of principal excitatory cells via their GABAA receptors and thus adjust excitatory output of neuronal circuits. The goal of this study was to examine the potential anti-convulsive effects of the neuro-active amino acid taurine, in the mouse model of limbic seizures. We used the glutamic acid decarboxylase (GAD) inhibitor isoniazid (100 mg.kg-1, s.c.) which induces seizures by interfering with GABA synthesis through inhibition of GAD activity followed by kainic acid (5 mg.kg-1, s.c.) a glutamate receptor agonist which is commonly used to induce limbic seizures.Using intracerebral recordings of field potentials found that taurine (43 mg.kg-1, s.c.) had a significant anti-epileptic effect when injected prior to isoniazid and KA. Furthermore, injection of taurine to a mouse undergoing limbic seizure completely stopped burst population spikes and restored neuronal firing to its baseline. Therefore, taurine is potentially capable of treating seizure-associated brain damage.

Hyperreflexia and enhanced ripple oscillations in the taurine-deficient mice.

In this study, we examined neuronal excitability and skeletal muscle physiology and histology in homozygous knockout mice lacking cysteine sulfonic acid decarboxylase (CSAD-KO). Neuronal excitability was measured by intracerebral recording from the prefrontal cortex. Skeletal muscle response was measured through stretch reflex in the ankle muscles. Specifically, we measured the muscle tension, amplitude of electromyogram and velocity of muscle response. Stretch reflex responses were evoked using a specialized stretching device designed for mice. The triceps surae muscle was stretched at various speeds ranging from 18 to 18,000° s-1. A transducer recorded the muscle resistance at each velocity and the corresponding EMG. We also measured the same parameter in anesthetized mice. We found that at each velocity, the CSAD-KO mice generated more tension and exhibited higher EMG responses. To evaluate if the enhanced response was due to neuronal excitability or changes in the passive properties of muscles, we anesthetize mice to eliminate the central component of the reflex. Under these conditions, CSAD-KO mice still exhibited an enhanced stretch reflex response, indicating ultrastructural alterations in muscle histology. Consistent with this, we found that sarcomeres from CSAD-KO muscles were shorter and thinner when compared to control sarcomeres. Neuronal excitability was further investigated using intracerebral recordings of brain waves from the prefrontal cortex. We found that extracellular field potentials in CSAD-KO mice were characterized by reduced amplitude of low-frequency brain waves (delta, theta, alpha, beta and gamma) and increased in the high low-frequency brain waves (slow and fast ripples). Increased slow and fast ripple rates serve as a biomarker of epileptogenic brain. We have previously shown that taurine interacts with GABAA receptors and induces biochemical changes in the GABAergic system. We suggest that taurine deficiency leads to alterations in the GABAergic system that contribute to the enhanced stretch reflex in CSAD-KO mice through biochemical mechanisms that involve alterations not only at the spinal level but also at the cortical level.

Antibiofilm activity of Actinobacillus pleuropneumoniae serotype 5 capsular polysaccharide.

Cell-free extracts isolated from colony biofilms of Actinobacillus pleuropneumoniae serotype 5 were found to inhibit biofilm formation by Staphylococcus aureus, S. epidermidis and Aggregatibacter actinomycetemcomitans, but not by A. pleuropneumoniae serotype 5 itself, in a 96-well microtiter plate assay. Physical and chemical analyses indicated that the antibiofilm activity in the extract was due to high-molecular-weight polysaccharide. Extracts isolated from a mutant strain deficient in the production of serotype 5 capsular polysaccharide did not exhibit antibiofilm activity. A plasmid harboring the serotype 5 capsule genes restored the antibiofilm activity in the mutant extract. Purified serotype 5 capsular polysaccharide also exhibited antibiofilm activity against S. aureus. A. pleuropneumoniae wild-type extracts did not inhibit S. aureus growth, but did inhibit S. aureus intercellular adhesion and binding of S. aureus cells to stainless steel surfaces. Furthermore, polystyrene surfaces coated with A. pleuropneumoniae wild-type extracts, but not with capsule-mutant extracts, resisted S. aureus biofilm formation. Our findings suggest that the A. pleuropneumoniae serotype 5 capsule inhibits cell-to-cell and cell-to-surface interactions of other bacteria. A. pleuropneumoniae serotype 5 capsular polysaccharide is one of a growing number of bacterial polysaccharides that exhibit broad-spectrum, nonbiocidal antibiofilm activity. Future studies on these antibiofilm polysaccharides may uncover novel functions for bacterial polysaccharides in nature, and may lead to the development of new classes of antibiofilm agents for industrial and clinical applications.

Broad-spectrum biofilm inhibition by Kingella kingae exopolysaccharide.

Cell-free extracts prepared from Kingella kingae colony biofilms were found to inhibit biofilm formation by Aggregatibacter actinomycetemcomitans, Klebsiella pneumoniae, Staphylococcus aureus, Staphylococcus epidermidis, Candida albicans, and K. kingae. The extracts evidently inhibited biofilm formation by modifying the physicochemical properties of the cell surface, the biofilm matrix, and the substrate. Chemical and biochemical analyses indicated that the biofilm inhibition activity in the K. kingae extract was due to polysaccharide. Structural analyses showed that the extract contained two major polysaccharides. One was a linear polysaccharide with the structure →6)-α-d-GlcNAcp-(1→5)-ß-d-OclAp-(2→, which was identical to a capsular polysaccharide produced by Actinobacillus pleuropneumoniae serotype 5. The second was a novel linear polysaccharide, designated PAM galactan, with the structure →3)-ß-d-Galf-(1→6)-ß-d-Galf-(1→. Purified PAM galactan exhibited broad-spectrum biofilm inhibition activity. A cluster of three K. kingae genes encoding UDP-galactopyranose mutase (ugm) and two putative galactofuranosyl transferases was sufficient for the synthesis of PAM galactan in Escherichia coli. PAM galactan is one of a growing number of bacterial polysaccharides that exhibit antibiofilm activity. The biological roles and potential technological applications of these molecules remain unknown.