Use of novel taurine-chitosan mediated liposomes for enhancing the oral absorption of doxorubicin via the TAUT transporter.

Our research aimed to enhance the oral bioavailability of doxorubicin hydrochloride (DOX·HCl) while minimizing the potential for myocardial toxicity. To achieve this goal, we developed a new method that utilizes a coating material to encapsulate the drug in liposomes, which can specifically target intestinal taurine transporter proteins. This coating material, TAU-CS, was created by combining taurine with chitosan. We characterized TAU-CS using various methods, including 1H NMR, FT-IR, and scanning electron microscopy (SEM). The resulting liposomes exhibited a regular spherical morphology, with a particle size of 195.7 nm, an encapsulation efficiency of 91.23 %, and a zeta potential of +11.65 mV. Under simulated gastrointestinal conditions, TAU-CS/LIP@DOX·HCl exhibited good stability and slow release. Pharmacokinetic studies revealed that, compared with DOX·HCl, TAU-CS/LIP@DOX·HCl had a relative bioavailability of 342 %. Intracellular uptake, immunofluorescence imaging, and permeation assays confirmed that the taurine transporter protein mediates the intestinal uptake of these liposomes. Our study suggested that liposomes coated with TAU-CS could serve as an effective oral delivery system and that targeting the taurine transporter protein shows promise in enhancing drug absorption.

24-Week ß-alanine ingestion does not affect muscle taurine or clinical blood parameters in healthy males.

PURPOSE: To investigate the effects of chronic beta-alanine (BA) supplementation on muscle taurine content, blood clinical markers and sensory side-effects. METHODS: Twenty-five healthy male participants (age 27 ± 4 years, height 1.75 ± 0.09 m, body mass 78.9 ± 11.7 kg) were supplemented with 6.4 g day-1 of sustained-release BA (N = 16; CarnoSyn™, NAI, USA) or placebo (PL; N = 9; maltodextrin) for 24 weeks. Resting muscle biopsies of the m. vastus lateralis were taken at 0, 12 and 24 weeks and analysed for taurine content (BA, N = 12; PL, N = 6) using high-performance liquid chromatography. Resting venous blood samples were taken every 4 weeks and analysed for markers of renal, hepatic and muscle function (BA, N = 15; PL, N = 8; aspartate transaminase; alanine aminotransferase; alkaline phosphatase; lactate dehydrogenase; albumin; globulin; creatinine; estimated glomerular filtration rate and creatine kinase). RESULTS: There was a significant main effect of group (p = 0.04) on muscle taurine, with overall lower values in PL, although there was no main effect of time or interaction effect (both p > 0.05) and no differences between specific timepoints (week 0, BA: 33.67 ± 8.18 mmol kg-1 dm, PL: 27.75 ± 4.86 mmol kg-1 dm; week 12, BA: 35.93 ± 8.79 mmol kg-1 dm, PL: 27.67 ± 4.75 mmol kg-1 dm; week 24, BA: 35.42 ± 6.16 mmol kg-1 dm, PL: 31.99 ± 5.60 mmol kg-1 dm). There was no effect of treatment, time or any interaction effects on any blood marker (all p > 0.05) and no self-reported side-effects in these participants throughout the study. CONCLUSIONS: The current study showed that 24 weeks of BA supplementation at 6.4 g day-1 did not significantly affect muscle taurine content, clinical markers of renal, hepatic and muscle function, nor did it result in chronic sensory side-effects, in healthy individuals. Since athletes are likely to engage in chronic supplementation, these data provide important evidence to suggest that supplementation with BA at these doses for up to 24 weeks is safe for healthy individuals.

A Systematic Risk Assessment and Meta-Analysis on the Use of Oral ß-Alanine Supplementation.

ß-Alanine supplementation is one of the world's most commonly used sports supplements, and its use as a nutritional strategy in other populations is ever-increasing, due to evidence of pleiotropic ergogenic and therapeutic benefits. Despite its widespread use, there is only limited understanding of potential adverse effects. To address this, a systematic risk assessment and meta-analysis was undertaken. Four databases were searched using keywords and Medical Subject Headings. All human and animal studies that investigated an isolated, oral, ß-alanine supplementation strategy were included. Data were extracted according to 5 main outcomes, including 1) side effects reported during longitudinal trials, 2) side effects reported during acute trials, 3) effect of supplementation on circulating health-related biomarkers, 4) effect of supplementation on skeletal muscle taurine and histidine concentration, and 5) outcomes from animal trials. Quality of evidence for outcomes was ascertained using the Grading of Recommendations Assessment Development and Evaluation (GRADE) framework, and all quantitative data were meta-analyzed using multilevel models grounded in Bayesian principles. In total, 101 human and 50 animal studies were included. Paraesthesia was the only reported side effect and had an estimated OR of 8.9 [95% credible interval (CrI): 2.2, 32.6] with supplementation relative to placebo. Participants in active treatment groups experienced similar dropout rates to those receiving the placebo treatment. ß-Alanine supplementation caused a small increase in circulating alanine aminotransferase concentration (effect size, ES: 0.274, CrI: 0.04, 0.527), although mean data remained well within clinical reference ranges. Meta-analysis of human data showed no main effect of ß-alanine supplementation on skeletal muscle taurine (ES: 0.156; 95% CrI: -0.38, 0.72) or histidine (ES: -0.15; 95% CrI: -0.64, 0.33) concentration. A main effect of ß-alanine supplementation on taurine concentration was reported for murine models, but only when the daily dose was ≥3% ß-alanine in drinking water. The results of this review indicate that ß-alanine supplementation within the doses used in the available research designs, does not adversely affect those consuming it.

Impact of Taurine on the proliferation and apoptosis of human cervical carcinoma cells and its mechanism.

BACKGROUND: Cervical cancer has the fourth highest incidence and mortality rate of all cancers in women worldwide; it seriously harms their physical and mental health. The aim of this study was to observe the roles and preliminary mechanism of Taurine (Tau)-induced apoptosis in cervical cancer cells. METHODS: Cells from the human cervical cancer cell line SiHa were transfected with the recombinant plasmid pEGFP-N1-MST1 (mammalian sterile 20-like kinase 1); then, the cell proliferation activity was analyzed by the MTT assay, cell apoptosis by flow cytometry, and the related protein levels by Western blotting. RESULTS: Tau inhibited the proliferation of SiHa cells and induced apoptosis in these cells (the apoptotic rate was 21.95% in the Tau 160 mmol/L group and 30% in the Tau 320 mmol/L group), upregulated the expression of the MST1 (control, 0.53; Tau 40-320 mmol/L groups, 0.84-1.45) and Bax (control, 0.45; Tau 40-320 mmol/L groups, 0.64-1.51) proteins (P < 0.01), and downregulated the expression of Bcl-2 (control, 1.28, Tau 40-320 mmol/L groups, 0.93-0.47) (P < 0.01). The overexpression of MST1 promoted the apoptosis of SiHa cells, enhanced the apoptosis-inductive effects of Tau (P < 0.01), upregulated the expression of the proapoptotic proteins p73, p53, PUMA (p53 upregulated modulator of apoptosis), and caspase-3, and promoted the phosphorylation of YAP (Yes-associated protein). CONCLUSIONS: Tau inhibited the proliferation and induced the apoptosis of cervical cancer SiHa cells. The MST1 protein plays an important role in the Tau-induced apoptosis of cervical cancer cells.

In vitro comparison of efficacy of catheter locks in the treatment of catheter related blood stream infection.

BACKGROUND & AIMS: Venous access used for parenteral nutrition (PN) application is extremely important for patients with intestinal failure. Potential loss of venous access might be a catastrophy for the patient. Catheter infections are a serious complication of PN application. Systemic administration of antibiotics as well as local antibiotic locks into the catheter to sterilize the catheter are used to treat catheter infections. However, there is no clear recommendation applying use of antibiotic locks, that would specify the type and concentration of antimicrobial medication. Our objective were to compare the efficacy of different types of antimicrobial lock therapy (especially taurolidine) and their concentrations to eradicate infectious agents. METHODS: Bacterial strains of microorganisms (Staphylococcus epidermidis, Staphylococcus aureus, methicillin resistant S. aureus (MRSA), Pseudomonas aeruginosa, multidrug-resistant P. aeruginosa, Candida albicans) were used. Subsequently, the catheter was exposed to the microbes and then was incubated with a specific lock for 2 or 24 h at 37 °C. We used these locks: ethanol 70%, taurolidine, gentamicine in concentrations 0,5, 1 and 10 mg/ml and vancomycine in concentrations 1, 5, and 10 mg/ml. The number of remaining CFU (colony forming units) was compared after incubation. RESULTS: 70% ethanol and taurolidine were most effective for all studied microorganisms. Gentamicine was more effective than vancomycine. CONCLUSIONS: The most effective antimicrobial lock solutions to eradicate selected pathogenic agents were ethanol and taurolidine. Use of antibiotics is often effective after many hours of treatment and there is a risk of inadequate therapy.

Differential modulation of human GABAC-ρ1 receptor by sulfur-containing compounds structurally related to taurine.

BACKGROUND: The amino acid taurine (2-Aminoethanesulfonic acid) modulates inhibitory neurotransmitter receptors. This study aimed to determine if the dual action of taurine on GABAC-ρ1R relates to its structure. To address this, we tested the ability of the structurally related compounds homotaurine, hypotaurine, and isethionic acid to modulate GABAC-ρ1R. RESULTS: In Xenopus laevis oocytes, hypotaurine and homotaurine partially activate heterologously expressed GABAC-ρ1R, showing an increment in its deactivation time with no changes in channel permeability, whereas isethionic acid showed no effect. Competitive assays suggest that hypotaurine and homotaurine compete for the GABA-binding site. In addition, their effects were blocked by the ion-channel blockers picrotixin and Methyl(1,2,5,6-tetrahydropyridine-4-yl) phosphinic acid. In contrast to taurine, co-application of GABA with hypotaurine or homotaurine revealed that the dual effect is present separately for each compound: hypotaurine modulates positively the GABA current, while homotaurine shows a negative modulation, both in a dose-dependent manner. Interestingly, homotaurine diminished hypotaurine-induced currents. Thus, these results strongly suggest a competitive interaction between GABA and homotaurine or hypotaurine for the same binding site. "In silico" modeling confirms these observations, but it also shows a second binding site for homotaurine, which could explain the negative effect of this compound on the current generated by GABA or hypotaurine, during co-application protocols. CONCLUSIONS: The sulfur-containing compounds structurally related to taurine are partial agonists of GABAC-ρ1R that occupy the agonist binding site. The dual effect is unique to taurine, whereas in the case of hypotaurine and homotaurine it presents separately; hypotaurine increases and homotaurine decreases the GABA current.

Taurine and glutathione in plasma and cerebrospinal fluid in olanzapine treated patients with schizophrenia.

Oxidative stress has been implicated in the pathophysiology of schizophrenia. Taurine and glutathione (GSH) have antioxidant and central nervous system protective properties, and are proposed to be involved in the pathology of schizophrenia. The aim of this study was to compare the blood and cerebrospinal fluid (CSF) levels of taurine and GSH in patients with schizophrenia, medicated with oral olanzapine, compared with controls. In total, 37 patients with schizophrenia and 45 healthy volunteers were recruited. We found the plasma taurine levels to be elevated in patients compared with controls. No differences were, however, found between patients and controls regarding taurine in CSF or GSH concentrations in plasma and CSF. Moreover, in the patient group no correlations between taurine and GSH levels and the symptoms or function of the disorder were found. The higher levels of plasma but not CSF taurine in patients with schizophrenia treated with OLA may implicate the involvement of taurine in the pathophysiology of the disease. The absence of GSH differences both in plasma and CSF between patients and controls is interesting in the perspective of earlier research proposing a dysregulation of GSH metabolism as a vulnerability factor for the development of schizophrenia.

Efeitos agudos e repetidos da cocaína em ratas em diferentes condições hormonais: estudo dos mecanismos inibitórios e tóxicos no sistema nervoso central / Acute and repeated effects of cocaine in rats under different hormonal conditions: study of inhibitory and toxic mechanisms in the central nervous system

A sensibilização comportamental à cocaína consiste no aumento da resposta após uso repetido intermitente da substância, e tem sido apontada como um dos principais fatores que aumentam o risco do desenvolvimento da dependência. Indivíduos do sexo feminino têm mostrado efeitos mais intensos em resposta ao uso de psicoestimulantes do que os do sexo masculino, influenciados por diferenças hormonais. Além da neurotoxicidade induzida por sua ação nos sistemas dopaminérgico e glutamatérgico (excitatórios), a cocaína influencia a atividade dos sistemas inibitórios cerebrais (GABA e taurina), que se contrapõe aos sistemas acima. Objetivamos, portanto, verificar a influência dos hormônios femininos na neurotoxicidade da cocaína e nas adaptações dos sistemas inibitórios cerebrais, secundárias ao uso deste psicoestimulante em fêmeas. Para tanto, foram utilizadas ratas intactas hormonalmente ou ratas ovariectomizadas, recebendo reposição hormonal (progesterona e/ou estradiol) ou não. Estas foram sensibilizadas com doses repetidas de cocaína e seu comportamento (atividade locomotora e estereotipias) foi monitorado. Para avaliar a influência dos hormônios na neurotoxicidade da cocaína, foi realizado Teste Cometa em diferentes regiões cerebrais, para verificar lesão de DNA na célula neuronal. Para verificar a influência destes hormônios nos níveis extracelulares de GABA (e seus precursores, glutamato e glutamina) e de taurina no córtex pré-frontal medial, os animais foram submetidos a sessões de microdiálise após realização de cirurgia estereotáxica. Os resultados de comportamento indicaram apenas as fêmeas com presença endógena de estradiol e progesterona desenvolveram tanto sensibilização locomotora quanto estereotipia. Já a reposição de estradiol aumentou os comportamentos estereotipados após desafio à cocaína, enquanto as ratas que receberam reposição de progesterona, associada ou não ao estradiol, apresentaram menor escore de estereotipia após cocaína repetida. Tanto a exposição aguda quanto a sensibilização à cocaína induziram dano no DNA em diferentes regiões cerebrais das ratas, exceto no hipotálamo, onde o dano foi comparado ao das ratas que não receberam cocaína. A presença endógena de estrógeno e progesterona diminuiu o dano provocado pela administração de cocaína em todas as regiões cerebrais, mostrando que uma maior sensibilização em fêmeas pode estar relacionada ao desenvolvimento de neuroplasticidade nas regiões avaliadas. Os níveis extracelulares de GABA, de seus precursores e de taurina também sofreram alteração após exposição à cocaína. A administração aguda deste psicoestimulante aumentou os níveis de GABA, glutamato e taurina e diminuiu os níveis de glutamina no CPFm, de forma diferente se for considerada a condição hormonal. Já a sensibilização à cocaína provocou menor alteração nos níveis de GABA e de taurina e consequente aumento nos níveis de glutamato no CPFm das ratas com presença hormonal endógena. Estes resultados sugerem que uma maior sensibilização à cocaína em fêmeas pode estar relacionada a uma hipofuncionalidade dos sistemas inibitórios cerebrais decorrentes da presença endógena dos hormônios sexuais femininos. Portanto, a sensibilização à cocaína em fêmeas com presença hormonal (principalmente o estrógeno) está relacionada ao desenvolvimento de neuroplasticidade e a uma menor atividade dos sistemas inibitórios cerebrais, com consequente aumento na atividade excitatória no CPFm, uma das regiões cerebrais mais importantes no desenvolvimento da adição.

Behavioral sensitization to cocaine is an increased response after repeated intermittent use of the substance, and has been identified as one of the main factors that increase the risk of developing addiction. Females have shown higher effects in response to psychostimulant use than males, influenced by hormonal differences. In addition to the induction of dopaminergic and glutamatergic (excitatory) neurotoxicity, cocaine influences the activity of brain systems inhibitory (GABA and taurine), which is opposite to the above systems. We aim therefore to investigate the influence of female hormones on cocaine neurotoxicity and in brain adaptations, secondary to this psychostimulant use in inhibitory systems of female rats. In this sense, we used hormonally intact rats or ovariectomized rats receiving hormone replacement therapy (progesterone and/or estrogen) or not. These were sensitized with repeated doses of cocaine and its behavior (locomotor activity and stereotypies) was monitored. To evaluate the influence of hormones on the neurotoxicity of cocaine, Comet Assay was performed in different brain areas, to verify DNA damage in neuronal cell. To check the influence of these hormones in extracellular levels of GABA (and its precursors, glutamate and glutamine) and taurine in the medial prefrontal cortex (mPFC), the animals were subjected to microdialysis session after performing stereotactic surgery. The behavior results indicated that only females with endogenous presence of both estrogen and progesterone developed sensitization by hyperlocomotion and stereotypy. The estradiol replacement increased stereotypic behaviors after cocaine challenge, while the rats that received progesterone replacement, associated or not with estradiol, had lower scores of stereotypy after repeated cocaine. Both acute exposure and sensitization to cocaine induced DNA damage in different brain areas of female rats, except in the hypothalamus , where the damage was compared to the rats that did not receive cocaine. The presence of endogenous estrogen and progesterone decreased the damage caused by the administration of cocaine in all brain areas, showing that greater sensitization in females may be associated to neuroplasticity development in the evaluated areas. Extracellular levels of GABA, its precursors and taurine also been changed after cocaine exposure. Acute administration of cocaine increased levels of GABA, glutamate and taurine and decreased glutamine levels in mPFC, differently according with the hormonal condition. Already cocaine sensitization caused less change in the levels of GABA and taurine and subsequent increased levels of glutamate in the mPFC of rats with endogenous hormonal presence. These results suggest that greater sensitization to cocaine in females may be related to a hypofunction of brain inhibitory systems resulting from the presence of endogenous female sex hormones. Therefore, sensitization to cocaine in females with hormonal presence (especially the estrogen) is related to the neuroplasticity development and a lower inhibitory activity of brain systems, with a consequent increase in excitatory activity in the mPFC, one of the most important brain areas involved in the drug addition.

Specificity of the volume-activated amino acid efflux pathway in cultured human breast cancer cells.

It has been shown that cell swelling stimulates the efflux of taurine from MCF-7 and MDA-MB-231 cells via a pathway which has channel-like properties. The purpose of this study was to examine the specificity of the volume-activated taurine efflux pathway in both cell lines. A hyposmotic shock increased the efflux of glycine, L-alanine, AIB (α-aminoisobutyric acid), D-aspartate but not L-leucine from MDA-MB-231 and MCF-7 cells. It was evident that the time course of activation/inactivation of those amino acids whose efflux was affected by cell swelling was similar to that of volume-activated taurine efflux. The effect of exogenous ATP on swelling-induced glycine, AIB and D-aspartate efflux from MDA-MB-231 cells was similar to that found on taurine efflux. In addition, volume-activated AIB efflux from MDA-MB-231 cells, like that of swelling-induced taurine efflux, was inhibited by diiodosalicylate. Tamoxifen inhibited volume-activated taurine release from both MDA-MB-231 and MCF-7 cells. The results suggest that neutral and anionic α-amino acids are able to utilize the volume-activated taurine efflux pathway in both cell lines. The effect of tamoxifen on breast cancer growth may, in part, be related to perturbations in cell volume regulation.

Taurine deficiency in thalassemia major-induced osteoporosis treated with neridronate.

The aetiology of thalassemia major-induced osteoporosis is multifactorial. Up to now, bisphosphonates seem to be a promising therapy. Taurine is found in a high concentration in bone cells enhancing bone tissue formation and inhibiting bone loss. Recently we found a decrease taurine plasma level in children affected by osteogenesis imperfecta during neridronate (amino-bisphosphonate) therapy suggesting a possible interaction between pharmacological effect of this drug and taurine availability. On the basis of these results, we performed plasma and urine amino acid (AA) analysis in thalassemia major-induced osteoporosis before and after 12 months of neridronate treatment. Twelve patients, five males and seven females, aged from 20 to 29 years following a hypertransfusion treatment protocol were enrolled in the study. Patients were treated with neridronate infusion every one month (30 mg in 100ml of saline). Plasma and urine specimens for AA analysis, bone mineral density, bone mineral content and vertebral project area were examined at baseline (T0) and after 12 months of treatment (T12). A significant decrease was observed for plasma level and urinary excretion of taurine (T0 vs. T12=p<0.01) whereas bone mineral content and vertebral projection area showed a statistical significant increase (T0 vs. T12=p<0.05). These results and other experimental researches warrant further studies examining the long-term effect of taurine supplementation in association with neridronate treatment.

Cadmium chloride exposure modifies amino acid daily pattern in the mediobasal hypothalamus in adult male rat.

The present study was conducted to investigate the possible effects of cadmium exposure on the daily pattern of aspartate, glutamate, glutamine, gamma-aminobutyric acid (GABA) and taurine levels in the mediobasal hypothalamus of adult male rats. For this purpose, animals were treated with cadmium at two different exposure doses (25 and 50 mg l(-1) of cadmium chloride, CdCl(2)) in the drinking water for 30 days. Control age-matched rats received CdCl(2)-free water. After the treatment, rats were killed at six different time intervals throughout a 24 h cycle. CdCl(2) exposure modified the amino acid daily pattern, as it decreased aspartate, glutamate, GABA and taurine levels at 12:00 h with both exposure doses employed. In addition, the treatment with 25 mg l(-1) of CdCl(2) induced the appearance of minimal values at 16:00 h and maximal values between 04:00 and 08:00 h for glutamate, and a peak of glutamine content at 20:00 h. The heavy metal also decreased GABA medium levels around the clock in the mediobasal hypothalamus. However, CdCl(2) did not alter the metabolic correlation between glutamate, aspartate, glutamine and GABA observed in control animals. These results suggest that CdCl(2) induced several alterations in aspartate, glutamate, glutamine, GABA and taurine daily pattern in the mediobasal hypothalamus and those changes may be related to alterations in hypothalamic function.

Aminomethylpiperazines as selective urotensin antagonists.

Aminomethylpiperazines, reported previously as being kappa-opioid receptor agonists, were identified as lead compounds in the development of selective urotensin receptor antagonists. Optimized substitution of the piperazine moiety has provided high affinity urotensin receptor antagonists with greater than 100-fold selectivity over the kappa-opioid receptor. Select compounds were found to inhibit urotensin-induced vasoconstriction in isolated rat aortic rings consistent with the hypothesis that an urotensin antagonist may be useful for the treatment of hypertension.

Characteristics of taurine release in slices from adult and developing mouse brain stem.

Taurine has been thought to function as a regulator of neuronal activity, neuromodulator and osmoregulator. Moreover, it is essential for the development and survival of neural cells and protects them under cell-damaging conditions. Taurine is also involved in many vital functions regulated by the brain stem, including cardiovascular control and arterial blood pressure. The release of taurine has been studied both in vivo and in vitro in higher brain areas, whereas the mechanisms of release have not been systematically characterized in the brain stem. The properties of release of preloaded [(3)H]taurine were now characterized in slices prepared from the mouse brain stem from developing (7-day-old) and young adult (3-month-old) mice, using a superfusion system. In general, taurine release was found to be similar to that in other brain areas, consisting of both Ca(2+)-dependent and Ca(2+)-independent components. Moreover, the release was mediated by Na(+)-, Cl(-)-dependent transporters operating outwards, as both Na(+)-free and Cl(-) -free conditions greatly enhanced it. Cl(-) channel antagonists and a Cl(-) transport inhibitor reduced the release at both ages, indicating that a part of the release occurs through ion channels. Protein kinases appeared not to be involved in taurine release in the brain stem, since substances affecting the activity of protein kinase C or tyrosine kinase had no significant effects. The release was modulated by cAMP second messenger systems and phospholipases at both ages. Furthermore, the metabotropic glutamate receptor agonists likewise suppressed the K(+)-stimulated release at both ages. In the immature brain stem, the ionotropic glutamate receptor agonists N-methyl-D-aspartate (NMDA) and 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) potentiated taurine release in a receptor-mediated manner. This could constitute an important mechanism against excitotoxicity, protecting the brain stem under cell-damaging conditions.

Effects of acute and chronic lamotrigine treatment on basal and stimulated extracellular amino acids in the hippocampus of freely moving rats.

The antiepileptic drug lamotrigine (LTG) is a relatively novel anticonvulsant frequently used in polytherapy and increasingly in monotherapy. LTG is believed to act by reducing excitatory glutamate (GLU) release due to an inhibition of Na(+) channels. In the present study, we have investigated the effects of acute and chronic (up to 21 days) treatment with LTG on basal and either veratridine- or KCl-stimulated release of aspartate (ASP), GLU, taurine (TAU) and GABA in the hippocampus of freely moving rats using microdialysis. Additionally, we have measured LTG concentrations in the plasma, whole brain and extracellular fluid of rats at the same time points. LTG significantly reduced basal ASP and GLU but only at the highest dose used (20 mg/kg) and was entirely without effect on basal TAU or GABA. When either veratridine or 100 mM KCl were added to the infusion medium amino acid release was evoked although the extent of this varied from one amino acid to another. LTG (10 mg/kg) reduced veratridine-evoked release of all four amino acids studied, although this was most marked in the case of GLU. LTG had no effect on KCl-stimulated amino acid release. When given for up to 21 days (2 x 5 mg/kg/day), LTG had no effect on basal amino acid levels. In contrast, LTG demonstrated over the time period studied an increasingly inhibitory effect on veratridine-evoked amino acid release. This effect of the drug was proportionally much greater in the case of GLU than for the other three amino acids studied. Measurement of plasma, whole brain tissue and extracellular LTG showed that in each of these compartments, it had reached an apparent steady state within 4 days of commencement of treatment and appeared to mirror the neurochemical changes measured. Our estimate of plasma LTG indicates that during chronic study, this was well within the therapeutic range, suggesting that the current neurochemical observations are clinically relevant.

Glutamine: recent developments in research on the clinical significance of glutamine.

PURPOSE OF REVIEW: The aim of this review is to describe the clinical relevance of supplementation of glutamine from the recent literature. First, new basic research is examined and subsequently recent clinical trials and a metaanalysis are illustrated. RECENT FINDINGS: Glutamine has a major impact on the functionality of the immune system. It has recently been established that glutamine not only has a protective effect on cells of the immune system, but also on other cells of the body, for instance cardiomyocytes. Evidence is accumulating for an effect of glutamine via glutathione, heat shock proteins as well as taurine. Another area of interest is the way glutamine enhances gut barrier function. More and more research is concentrating on the positive effect of glutamine on the gut-associated lymphoid tissue. SUMMARY: Based on a recent meta-analysis and up-to-date clinical trials, we may conclude that glutamine has a beneficial effect on infectious complications and reduces hospital stay. In critically ill patients glutamine supplementation may reduce morbidity and mortality. The greatest effect was observed in patients receiving high dose parenteral glutamine. A recent study with high dose enteral glutamine demonstrated a reduced mortality in the glutamine supplemented group. In the future more trials with larger numbers of participants are needed, especially with high dose enteral glutamine in the perioperatively and the intensive care unit setting.

Possible roles of sulfur-containing amino acids in a chemoautotrophic bacterium-mollusc symbiosis.

Invertebrate hosts of chemoautotrophic symbionts face the unique challenge of supplying their symbionts with hydrogen sulfide while avoiding its toxic effects. The sulfur-containing free amino acids taurine and thiotaurine may function in sulfide detoxification by serving as sulfur storage compounds or as transport compounds between symbiont and host. After sulfide exposure, both taurine and thiotaurine levels increased in the gill tissues of the symbiotic coastal bivalve Solemya velum. Inhibition of prokaryotic metabolism with chloramphenicol, inhibition of eukaryotic metabolism with cycloheximide, and inhibition of ammonia assimilation with methionine sulfoximine reduced levels of sulfur-containing amino acids. Chloramphenicol treatment inhibited the removal of sulfide from the medium. In the absence of metabolic inhibitors, estimated rates of sulfide incorporation into taurine and thiotaurine accounted for nearly half of the sulfide removed from the medium. In contrast, amino acid levels in the nonsymbiotic, sulfide-tolerant molluscs Geukensia demissa and Yoldia limatula did not change after sulfide exposure. These findings suggest that sulfur-containing amino acids function in sulfide detoxification in symbiotic invertebrates, and that this process depends upon ammonia assimilation and symbiont metabolic capabilities.

Stimulation by surangin B of endogenous amino acid release from synaptosomes.

The effect of surangin B, an insecticidal natural product coumarin, on presynaptic release of endogenous amino acids was investigated using a purified synaptosomal fraction isolated from mouse brain. Surangin B stimulated the release of glutamic acid (GLU), gamma-aminobutyric acid (GABA), serine, alanine and the aminosulfonic acid taurine from synaptosomes at micromolar concentrations. In all cases, these responses were reduced by removing calcium from the saline and surangin B-evoked release of GLU, GABA, aspartic acid (ASP) and alanine was significantly inhibited by the sodium channel blocker tetrodotoxin. Rotenone (a complex I inhibitor) and carbonyl cyanide chlorophenylhydrazone (CCCP; an uncoupler), were more potent releasers of amino acids from synaptosomes than surangin B, however, carboxin (a complex II-selective inhibitor), was extremely weak to ineffective in this regard. The stimulatory effect of surangin B and complex III-selective inhibitors on release of GLU, GABA, ASP and alanine by synaptosomes was significantly reduced by N,N,N',N'-tetramethyl-p-phenylenediamine, suggesting that blockade of complex III in intraterminal mitochondria is an important effect of this coumarin. Our results demonstrate that surangin B, in common with CCCP and inhibitors of complex I and III, cause release of both neurotransmitter and non-neurotransmitter amino acids from nerve endings in vitro. However, in contrast to most classical agents which interfere selectively with mitochondrial function, the release of endogenous amino acids from synaptosomes by surangin B also involves a moderate extracellular calcium ion-dependent component and relies partially on sodium ion entry into the nerve ending.

Effects of chronic administration of bilobalide on amino acid levels in mouse brain.

We have previously demonstrated that 4-day-treatment of mice with bilobalide, a sesquiterpene of Ginkgo biloba L., increases GABA levels in mouse brain, but, effects of chronic treatment with it are not clear. To study effects of chronic treatment of mice with bilobalide on amino acid levels in the brain, we determined the levels of aspartate, glutamate, serine, glutamine, glycine, taurine and GABA in the hippocampus, striatum and cortex. Bilobalide (3 mg/kg/day) was administered orally to 4-week-old mice for 40 days. Bilobalide treatment resulted in a significant increase in the levels of glutamate, aspartate, gamma-aminobutyric acid (GABA), and glycine in the hippocampus of mice compared with the control. An increased level of glycine after bilobalide treatment was also detected in the striatum. In the cortex, bilobalide increased the GABA level, whereas it decreased the level of aspartate. These changes in the levels of various amino acids may be involved in the broad spectrum of pharmacological activities of the extract of Ginkgo biloba on the central nervous system.

A microdialysis study of the novel antiepileptic drug levetiracetam: extracellular pharmacokinetics and effect on taurine in rat brain.

Using a rat model which allows serial blood sampling and concurrent brain microdialysis sampling, we have investigated the temporal kinetic inter-relationship of levetiracetam in serum and brain extracellular fluid (frontal cortex and hippocampus) following systemic administration of levetiracetam, a new antiepileptic drug. Concurrent extracellular amino acid concentrations were also determined. After administration (40 or 80 mg kg(-1)), levetiracetam rapidly appeared in both serum (T(max), 0.4 - 0.7 h) and extracellular fluid (T(max), 2.0 - 2.5 h) and concentrations rose linearly and dose-dependently, suggesting that transport across the blood-brain barrier is rapid and not rate-limiting. The serum free fraction (free/total serum concentration ratio; mean+/-s.e.mean range 0.93 - 1.05) was independent of concentration and confirms that levetiracetam is not bound to blood proteins. The kinetic profiles for the hippocampus and frontal cortex were indistinguishable suggesting that levetiracetam distribution in the brain is not brain region specific. However, t(1/2) values were significantly larger than those for serum (mean range, 3.0 - 3.3 h vs 2.1 - 2.3 h) and concentrations did not attain equilibrium with respect to serum. Levetiracetam (80 mg kg(-1)) was associated with a significant reduction in taurine in the hippocampus and frontal cortex. Other amino acids were unaffected by levetiracetam. Levetiracetam readily and rapidly enters the brain without regional specificity. Its prolonged efflux from and slow equilibration within the brain may explain, in part, its long duration of action. The concurrent changes in taurine may contribute to its mechanism of action.