Taurine modulates calcium influx through L-type voltage-gated calcium channels in isolated cochlear outer hair cells in guinea pigs

Taurine as a potential therapeutic agent interacting with multiple signaling pathways implicated in autism spectrum disorder (ASD): An in-silico analysis

Autism spectrum disorders (ASD) are a complex sequelae of neurodevelopmental disorders which manifest in the form of communication and social deficits. Currently, only two agents, namely risperidone and aripiprazole have been approved for the treatment of ASD, and there is a dearth of more drugs for the disorder. The exact pathophysiology of autism is not understood clearly, but research has implicated multiple pathways at different points in the neuronal circuitry, suggesting their role in ASD. Among these, the role played by neuroinflammatory cascades like the NF-KB and Nrf2 pathways, and the excitotoxic glutamatergic system, are said to have a bearing on the development of ASD. Similarly, the GPR40 receptor, present in both the gut and the blood brain barrier, has also been said to be involved in the disorder. Consequently, molecules which can act by interacting with one or multiple of these targets might have a potential in the therapy of the disorder, and for this reason, this study was designed to assess the binding affinity of taurine, a naturally-occurring amino acid, with these target molecules. The same was scored against these targets using in-silico docking studies, with Risperidone and Aripiprazole being used as standard comparators. Encouraging docking scores were obtained for taurine across all the selected targets, indicating promising target interaction. But the affinity for targets actually varied in the order NRF-KEAP > NF-κB > NMDA > Calcium channel > GPR 40. Given the potential implication of these targets in the pathogenesis of ASD, the drug might show promising results in the therapy of the disorder if subjected to further evaluations.

Taurine prevents MK-801-induced shoal dispersion and altered cortisol responses in zebrafish

Schizophrenia is a chronic neuropsychiatric disorder characterized by a shortened lifespan and significant impaired social and vocational functioning. Schizophrenic patients can present hypothalamic-pituitary-adrenal (HPA) axis dysfunctions and cortisol dysregulation, which play an important role on the etiology onset, exacerbation, and relapsing of symptoms. Based on its intrinsic neuroprotective properties, taurine is considered a promising substance with beneficial role on various brain disorders, including schizophrenia. Here, we evaluated the effects of taurine on shoaling behavior and whole-body cortisol levels in zebrafish treated with dizocilpine (MK-801), which elicits schizophrenia-like phenotypes in animal models. Briefly, zebrafish shoals (4 fish per shoal) were exposed to dechlorinated water or taurine (42, 150, or 400 mg/L) for 60 min. Then, saline (PBS, pH 7.4 or 2.0 mg/kg MK-801) were intraperitoneally injected and zebrafish behavior was recorded 15 min later. In general, MK-801 disrupted shoaling behavior and reduced whole-body cortisol levels in zebrafish. All taurine pretreatments prevented MK-801-induced increase in shoal area, while 400 mg/L taurine prevented the MK-801-induced alterations in neuroendocrine responses. Moreover, all taurine-pretreated groups showed increased geotaxis, supporting a modulatory role in the overall dispersion pattern of the shoal. Collectively, our novel findings show a potential protective effect of taurine on MK-801-induced shoal dispersion and altered neuroendocrine responses, fostering the use of zebrafish models to assess schizophrenia-like phenotypes.

Taurine enhances mouse cochlear neural stem cell transplantation via the cochlear lateral wall for replacement of degenerated spiral ganglion neurons via sonic hedgehog signaling pathway

The aim of this paper is to investigate the potential beneficial effects of taurine in cochlear neural stem cell (NSC) transplantation and elucidate the underlying molecular mechanism. The NSC cells were isolated from neonatal Balb/c mice and an auditory neuropathy gerbil model was established by microinjection of ouabain. The spiral ganglion neurons (SGN) were characterized with immunofluorescence stained with Tuj1 antibody. Cell proliferation was determined by BrdU incorporation assay and the morphologic index was measured under the light microscope. The relative protein level was determined by immunoblotting. The hearing of the animal model was scored by click- and tone burst-evoked auditory brainstem response (ABR). Here we consolidated our previous finding that taurine stimulated SGN density and the proliferation index, which were completely abolished by Shh inhibitor, cyclopamine. Transplantation of cochlear NSCs combined with taurine significantly improved ouabain-induced auditory neuropathy in gerbils. In addition, cyclopamine antagonized taurine's effect on glutamatergic and GABAergic neuron population via suppression of VGLUT1 and GAT1 expression. Mechanistically, taurine evidently activated the Sonic HedgeHog pathway and upregulated Shh, Ptc-1, Smo and Gli-1 proteins, which were specifically blockaded by cyclopamine. Here, for the first time demonstrated we that co-administration with taurine significantly improved NSC transplantation and the Shh pathway was identified in this beneficial effect.

Outer hair cells isolation from postnatal Sprague-Dawley rats

Outer hair cells (OHCs) damage is a general phenomenon in clinical disorders such as noise-induced hearing loss and drug-induced hearing loss. In order to elucidate the mechanism underlying these disorders, OHCs – its diseased region needs to be deeply investigated. However, OHCs array on the basilar membrane which contains massive cells with different types. Therefore, to isolate OHCs from this huge population is significant for revealing its pathological and molecular changes during disease processing. In the present study, we tried to isolate OHCs from the commonly used animal model –Sprague-Dawley (SD) rats. By separating outer hair cells from SD rats with different day ages, we found that 9 days after birth was a suitable time for the separation of the OHCs. At this time, the number of OHCs isolated from rats was large, and the cell morphology was typical of cylindrical shape. OHCs isolated using this method are histologically suitable and quantitatively adequate for molecular biological and electrophysiological analyses.

Early Effect of Amyloid β-Peptide on Hippocampal and Serum Metabolism in Rats Studied by an Integrated Method of NMR-Based Metabolomics and ANOVA-Simultaneous Component Analysis

Amyloid β (Aβ) deposition has been implicated in the pathogenesis of Alzheimer's disease. However, the early effect of Aβ deposition on metabolism remains unclear. In the present study, thus, we explored the metabolic changes in the hippocampus and serum during first 2 weeks of Aβ25-35 injection in rats by using an integrated method of NMR-based metabolomics and ANOVA-simultaneous component analysis (ASCA). Our results show that Aβ25-35 injection, time, and their interaction had statistically significant effects on the hippocampus and serum metabolome. Furthermore, we identified key metabolites that mainly contributed to these effects. After Aβ25-35 injection from 1 to 2 weeks, the levels of lactate, N-acetylaspartate, creatine, and taurine were decreased in rat hippocampus, while an increase in lactate and decreases in LDL/VLDL and glucose were observed in rat serum. Therefore, we suggest that the reduction in energy and lipid metabolism as well as an increase in anaerobic glycolysis may occur at the early stage of Aβ25-35 deposition.

Mechanisms Underlying Taurine Protection Against Glutamate-Induced Neurotoxicity

Taurine appears to exert potent protections against glutamate (Glu)-induced injury to neurons, but the underlying molecular mechanisms are not fully understood. The possibly protected targets consist of the plasma membrane and the mitochondrial as well as endoplasmic reticulum (ER) membranes. Protection may be provided through a variety of effects, including the prevention of membrane depolarization, neuronal excitotoxicity and mitochondrial energy failure, increases in intracellular free calcium ([Ca2+]i), activation of calpain, and reduction of Bcl-2 levels. These activities are likely to be linked spatially and temporally in the neuroprotective functions of taurine. In addition, events that occur downstream of Glu stimulation, including altered enzymatic activities, apoptotic pathways, and necrosis triggered by the increased [Ca2+]i, can be inhibited by taurine. This review discusses the possible molecular mechanisms of taurine against Glu-induced neuronal injury, providing a better understanding of the protective processes, which might be helpful in the development of novel interventional strategies.

Modes of direct modulation by taurine of the glutamate NMDA receptor in rat cortex

Taurine is an endogenous brain substance with robust neuromodulatory and possible neuroprotective properties. Though other mechanisms of action have been reported, its interaction with the NMDA (N-methyl-D-aspartic acid) receptor is undocumented. We investigated taurine's interaction with the NMDA receptor using electrophysiological and receptor binding approaches. The effects of taurine on field potential responses in layer-5 of prelimbic cortex in rat brain slices evoked by single-pulse electrical stimulation of ventral medial cortex were determined. Picrotoxin (80 µM) was present in all control and drug solutions to block the Cl(-) channels associated with the GABA-, taurine-, and strychnine sensitive glycine- receptors. A typical response consisted of an NBQX (2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo-[f]-quinoxaline-7-sulfonamide)-sensitive negative wave (N1) followed by a positive wave (P1) and a broad negativity (N2), both sensitive to dl-AP5 (dl-2-amino-5-phosphonopentanoic acid) inhibition. Taurine exerted a 41.5 ± 8.3% (n = 9) voltage reduction within the late phase of N2. This taurine action was prevented by 100 µM AP5, but not by 10 µM nifedipine, supporting a direct modulation of NMDA receptor function by taurine, without requiring the involvement of the L-type Ca(2+) channel. Taurine did not alter specific [(3)H] MK-801 binding to rat cortical membranes in the presence of glycine or glutamate; but inhibited spermine-potentiated specific [(3)H] MK-801 binding to NMDA receptors by 15-20% in the presence of glycine. In addition, taurine reduced the apparent affinity of the NMDA receptor for glycine (in the presence of spermine) by 10-fold. These results show that taurine interacts directly with the NMDA receptor by multiple mechanisms.

Effects of taurine-magnesium coordination compound on ionic channels in rat ventricular myocytes of arrhythmia induced by ouabain

Taurine-magnesium coordination compound (TMCC) has anti-arrhythmic effects. The aim of the present study was to explore the targets of the anti-arrhythmic effect of TMCC and the electrophysiological effects of TMCC on ouabain-induced arrhythmias in rat ventricular myocytes. Sodium current (I(Na)), L-type calcium current (I(ca, L)), and transient outward potassium current (I(to)) were measured and analyzed using whole-cell patch-clamp recording technique in normal rat cardiac myocytes and rat ventricular myocytes of arrhythmia induced by ouabain. In isolated ventricular myocytes, I(Na) and I(to) were blocked by TMCC (100, 200, 400 μM) in a concentration-dependent manner, and the effects of TMCC (400 μM) were equal to that of amiodarone. However, I (ca, L) was moderately increased by TMCC (400 μM) while significantly decreased by amiodarone. Ouabain (5 μM) significantly decreased sodium, L-type calcium, and transient outward potassium currents. TMCC (100 μM) relieved abnormal sodium currents induced by ouabain through facilitation of steady-state inactivation. TMCC (200 and 400 μM) relieved abnormal L-type calcium currents induced by ouabain through facilitation of steady-state activation and retardation of steady-state inactivation. TMCC failed to further inhibit abnormal transient outward potassium currents induced by ouabain. However, amiodarone inhibited the decreasing sodium, L-type calcium, and transient outward potassium currents further. These data suggest that I(Na), I(ca, L), and I(to) may be the targets of the antiarrhythmic effect of TMCC, which can antagonize ouabain-induced changes of ionic currents in rat ventricular myocytes.

Investigation of toxicological effects of Shuanghuanglian injection in Beagle dogs by metabonomic and traditional approaches

In this study, clinical biochemistry, hematology, histopathology and (1)H nuclear magnetic resonance spectroscopy-based metabonomic approaches were applied to investigate the toxicological effects of Shuanghuanglian (SHL) injection after intravenous administration (dosed at 4, 12 and 36 mL stock/kg) in Beagle dogs for 30 d. Decreases in red blood cells, hemoglobin, mean cell volume, mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration were observed in the high-dose group. Elevated reticulocytes, total bilirubin and direct bilirubin were also observed in this group. Moreover, significant hemosiderosis and Prussian blue positivity were detected in the liver, spleen and kidney from high-dose group animals, and transmission electron microscopy examination revealed an appreciable number of acanthrocytes in the liver. These results collectively indicate that SHL injection has the potential to cause hemolytic anemia. Metabonomic analysis showed increases in serum lactate, choline and phosphocholine but a decrease in taurine in treated groups and these findings may underlie the toxicological mechanism of SHL injection. In summary, SHL injection shows hemolytic effects in Beagle dogs; moreover, serum choline and phosphocholine as well as lactate and taurine may be the biomarkers for hemolytic anemia induced by SHL injection.

The effect of supplemental dietary taurine on tinnitus and auditory discrimination in an animal model

Loss of central inhibition has been hypothesized to underpin tinnitus and impact auditory acuity. Taurine, a partial agonist at inhibitory glycine and γ-amino butyric acid receptors, was added to the daily diet of rats to examine its effects on chronic tinnitus and normal auditory discrimination. Eight rats were unilaterally exposed once to a loud sound to induce tinnitus. The rats were trained and tested in an operant task shown to be sensitive to tinnitus. An equivalent unexposed control group was run in parallel. Months after exposure, 6 of the exposed rats showed significant evidence of chronic tinnitus. Two concentrations of taurine in drinking water were given over several weeks (attaining average daily doses of 67 mg/kg and 294 mg/kg). Water consumption was unaffected. Three main effects were obtained: (1) The high taurine dose significantly attenuated tinnitus, which returned to near pre-treatment levels following washout. (2) Auditory discrimination was significantly improved in unexposed control rats at both doses. (3) As indicated by lever pressing, taurine at both doses had a significant group-equivalent stimulant effect. These results are consistent with the hypothesis that taurine attenuates tinnitus and improves auditory discrimination by increasing inhibitory tone and decreasing noise in the auditory pathway.