Significance of Taurine in the Brain.

Two main functions of taurine in the brain are here discussed: the role of taurine in cell volume regulation and the neuromodulatory actions of taurine liberated by depolarization. Taurine takes part in cell volume regulation with other small-molecular compounds. Extracellular taurine inhibits neuronal firing through GABA and glycine receptors. However, the existence of specific taurine receptors is still not excluded.

Comparison of Toxicity of Taurine and GABA in Combination with Alcohol in 7-Day-Old Mice.

Previously, we described the combined toxicity of taurine and alcohol, and assumed hypoglycemia to be one reason of this toxicity. To understand whether taurine-ethanol combined toxicity is exclusively connected to taurine or whether other inhibitory amino acids may have similar effects when combined with ethanol, we tested different doses of gamma-aminobutyric acid (GABA) in combination with ethanol in 7-day-old mice. The minimal dose of GABA in combination with 5 g/kg ethanol which could kill a mouse was 2 g/kg. GABA combined with ethanol at doses of 3 g/kg, 4 g/kg, 6 g/kg induced lethality of 30%, 90% and 100%, correspondingly. Taurine at the doses of 4 and 6 g/kg combined with ethanol induced death in 60 and 100% of mice. Ethanol (5 g/kg), taurine (6 g/kg), GABA (4 g/kg) administered alone and the combination of ethanol (5 g/kg) with taurine (3 g/kg) have no lethal effects. GABA (6 g/kg) applied alone induced 90% lethality. Taurine or GABA alone decreased blood glucose in a dose-depending manner. Ethanol potentiated GABA- and taurine-induced decrease in blood glucose and in some animals it dropped from 8.8 (intact) to a hypoglycemic level 3.1-3.3 mmol/L (GABA 4 g/kg, taurine 6 g/kg), but this may not be considered a single reason of death. We conclude that the combination of GABA and ethanol has a lethal effect and this is stronger than the combined toxicity of ethanol and taurine.

Neurotoxicity of Ammonia.

Abnormal liver function has dramatic effects on brain functions. Hyperammonemia interferes profoundly with brain metabolism, astrocyte volume regulation, and in particular mitochondrial functions. Gene expression in the brain and excitatory and inhibitory neurotransmission circuits are also affected. Experiments with a number of pertinent animal models have revealed several potential mechanisms which could underlie the pathological phenomena occurring in hepatic encephalopathy.

Properties of Taurine Release in Glucose-Free Media in Hippocampal Slices from Developing and Adult Mice.

The release of preloaded [(3)H]taurine from hippocampal slices from developing 7-day-old and young adult 3-month-old mice was studied in a superfusion system in the absence of glucose. These hypoglycemic conditions enhanced the release at both ages, the effect being markedly greater in developing mice. A depolarizing K(+) concentration accentuated the release, which indicates that it was partially mediated by exocytosis. The anion channel blockers were inhibitory, witnessing the contribution of ion channels. NO-generating agents fomented the release as a sign of the participation of excitatory amino acid receptors. The other second messenger systems were apparently less efficient. The much greater taurine release could be a reason for the well-known greater tolerance of developing nervous tissue to lack of glucose.

Modulation by kynurenine of extracellular kynurenate and glutamate in cerebral cortex of rats with acute liver failure.

BACKGROUND: Kynurenic acid (KYNA) modulates the glutamatergic tone by controlling neuronal glutamate (GLU) release. The present study tested the potential of the KYNA precursor, kynurenine (KYN) to counter increased extracellular GLU associated with the pathogenesis of hepatic encephalopathy accompanying acute liver failure (ALF). METHODS: ALF was induced in adult rats by administration of a hepatotoxin, thioacetamide. KYNA and GLU were measured in the cerebral cortical microdialysates of control (saline-treated) and ALF rats using HPLC. The expression of mRNA coding for kynurenine aminotransferase II (KAT-II), the astrocytic enzyme converting KYN to KYNA, was assayed by real-time PCR. RESULTS: Cerebral cortical extracellular KYNA was increased in ALF rats not treated with KYN, consistent with a previously observed increase of cerebral cortical KATII activity in this ALF model. Single intraperitoneal administration of KYN (50 mg/kg, 120 min before microdialysate collection), produced a further substantial increase of extracellular KYNA, paralleled by a decrease of extracellular GLU. In cultured cerebral cortical astrocytes, the cells which in situ are the primary target of blood-derived ammonia and other toxins liberated due to ALF, elevation of KAT-II mRNA expression was noted upon their incubation with KYN and the KYN precursor, tryptophan (Trp), which is normally elevated by ALF. CONCLUSIONS: Administration of exogenous KYN to stimulate KYNA synthesis may help correcting excessive extracellular accumulation of GLU in cerebral cortex caused by ALF. The therapeutic potential of KYN in ALF appears to be fostered by increased expression of KAT-II in astrocytes upon exposure to KYN or Trp.

Lethality of taurine and alcohol coadministration in mice.

Alcohol consumption by mothers during pregnancy causes a fetal alcohol syndrome associated with massive neuronal apoptosis. We have recently shown that taurine at a dose of 2 g/kg saves about 50% of dying cerebellar neurons from ethanol-induced apoptosis in 7-day-old mice. However, a further increase in the taurine dose to ethanol-treated mice had a toxic and in some cases lethal effect. In the present work we studied the toxic effects of taurine and ethanol coadministration in three age groups: 7-day-old, adult (5 to 6 months old), and old (12 to 13 months old) mice. Taurine and ethanol were injected in two half-doses: taurine at 0 and 4 h and ethanol at 1 and 3 h. The minimal 100% lethal doses in coadministration of taurine and ethanol were the following: 7-day-old mice-6 g/kg taurine + 5 g/kg ethanol, adult mice-10 g/kg of taurine + 8 g/kg of ethanol, and old mice-above 6 g/kg of taurine + 6 g/kg of ethanol. All mice treated with taurine or ethanol alone survived. The adult and old mice dying from the combined toxicity of taurine and ethanol showed a marked fall in blood glucose, which may be one reason for lethality. A comparison of the lethal doses of taurine and ethanol coadministration in different age groups allows us to conclude that the adverse effect of the combined toxicity of taurine and ethanol is age dependent.

Regulation of taurine release in the hippocampus of developing and adult mice.

Taurine release in mouse hippocampal slices is regulated by several neurotransmitter receptor systems. The ionotropic glutamate receptors and the adenosine receptor A(1) are the most effective. The effect of N-methyl-D-aspartate receptors is mediated via activation of the pathway involving nitric oxide and 3',5'-cyclic guanosine monophosphate. The activation of excitatory amino acid receptors causes at the same time an increase in taurine release. The activation of adenosine A(1) receptors also potentiates taurine release. The taurine released may counteract any excitotoxic effects of glutamate, particularly in the developing hippocampus.

Ischemia induces release of endogenous amino acids from the cerebral cortex and cerebellum of developing and adult mice.

Ischemia enhanced release of endogenous neuroactive amino acids from cerebellar and cerebral cortical slices. More glutamate was released in adult than developing mice. Taurine release enhanced by K(+) stimulation and ischemia was more than one magnitude greater than that of GABA or glutamate in the developing cerebral cortex and cerebellum, while in adults the releases were almost comparable. Aspartate release was prominently enhanced by both ischemia and K(+) stimulation in the adult cerebral cortex. In the cerebellum K(+) stimulation and ischemia evoked almost 10-fold greater GABA release in 3-month olds than in 7-day olds. The release of taurine increased severalfold in the cerebellum of 7-day-old mice in high-K(+) media, whereas the K(+)-evoked effect was rather small in adults. In 3-month-old mice no effects of K(+) stimulation or ischemia were seen in the release of aspartate, glycine, glutamine, alanine, serine, or threonine. The releases from the cerebral cortex and cerebellum were markedly different and also differed between developing and adult mice. In developing mice only the release of inhibitory taurine may be large enough to counteract the harmful effects of excitatory amino acids in ischemia in both cerebral cortex and cerebellum, in particular since at that age the release of glutamate and aspartate cannot be described as massive.

Taurine and epilepsy.

Dysfunction of excitatory and inhibitory neurotransmitters or neuromodulators is thought to underlie epileptic symptoms. Taurine, 2-aminoethanesulfonate, is a ubiquitous free amino acid abounding in the brain of humans and most animal species. It hyperpolarizes neurons and inhibits their firing. It may be a participating factor in certain subpopulations of epilepsy patients but its deficiency is not a universal prerequisite for seizures. Here, the participation of taurine in animal seizure models and human epilepsy patients is reviewed.

Modulation of taurine release in glucose-free media by glutamate receptors in hippocampal slices from developing and adult mice.

Taurine has been thought to protect neural cells against cell-damaging conditions to which the hippocampus is particularly vulnerable. We studied now how the release of preloaded [(3)H]taurine is regulated by glutamate receptors in glucose-free media in slices prepared from the mouse hippocampus from developing (7 days old) and young adult (3 months old) mice, using a superfusion system. The lack of glucose enhanced taurine release more from slices from developing mice than from slices from adults. At both ages ionotropic glutamate agonists significantly increased the release in a receptor-mediated manner. Of the metabotropic glutamate receptors those belonging to the group III were effective. The release was enhanced in adult mice but attenuated in developing mice. Both effects were blocked by the receptor antagonists. The results show that glutamate receptors affect taurine release in the absence of glucose in which condition taurine should be neuroprotective.

Indoleamine 2,3-dioxygenase activity and expression in patients with chronic lymphocytic leukemia.

UNLABELLED: Indoleamine 2,3-dioxygenase (IDO) activity and expression is increased in many hematological malignancies, but has not been previously studied in chronic lymphocytic leukemia (CLL). We determined IDO activity and expression in 49 patients with CLL. We found that IDO activity is increased in CLL. This may have some influence on CLL progression. BACKGROUND: Indoleamine 2,3-dioxygenase (IDO) is an enzyme involved in the catabolism of tryptophan, suppressing T-cell activity. IDO activity and expression are increased in many malignant diseases, including hematological malignancies. IDO expression can mediate immunotolerance to tumors. IDO activity and expression have not previously been studied in chronic lymphocytic leukemia (CLL). METHODS: We measured IDO activity by calculating the kynurenine-tryptophan (kyn-trp) ratio. IDO and IDO2 gene expression was determined by using real-time polymerase chain reaction (PCR). RESULTS: In patients with CLL, the serum kyn-trp ratio--reflecting increased IDO activity--was significantly higher compared with controls, but in peripheral blood mononuclear cells (PBMCs)--mainly representing malignant B cells--the expression of genes encoding IDO and IDO2 enzymes was reduced. CONCLUSIONS: Increased IDO activity in patients with CLL may affect disease progression, although it originates from cells other than malignant B cells.

Taurine protects cerebellar neurons of the external granular layer against ethanol-induced apoptosis in 7-day-old mice.

Acute alcohol administration is harmful especially for the developing nervous system, where it induces massive apoptotic neurodegeneration leading to alcohol-related disorders of newborn infants. Neuroprotection against ethanol-induced apoptosis may save neurons and reduce the consequences of maternal alcohol consumption. Previously we have shown that taurine protects immature cerebellar neurons in the internal granular layer of cerebellum from ethanol-induced apoptosis. Now we describe a similar protective action for taurine in the external layer of cerebellum of 7-day-old mice. The mice were divided into three groups: ethanol-treated, ethanol + taurine-treated and controls. Ethanol (20% solution) was administered subcutaneously at a total dose of 5 g/kg (2.5 g/kg at time 0 h and 2.5 g/kg at 2 h) to the ethanol and ethanol + taurine groups. The ethanol + taurine group also received subcutaneously two injections of taurine (1 g/kg each, 1 h before the first dose of ethanol and 1 h after the second dose of ethanol). To verify apoptosis, immunostaining for activated caspase-3 and TUNEL staining were made in the mid-sagittal sections containing lobules I-X of the cerebellar vermis at 8 h after the first ethanol injection. Ethanol induced apoptosis in the cerebellar external granular layer. Taurine treatment significantly reduced the number of activated caspase-3-immunoreactive and TUNEL-positive cells. Taurine has thus a neuroprotective antiapoptotic action in the external granular layer of the cerebellum, preserving a number of neurons from ethanol-induced apoptosis.

Release of endogenous amino acids from the striatum from developing and adult mice in ischemia.

In most other studies the release of amino acid neurotransmitters and modulators in vitro has been studied mostly using labeled preloaded compounds. For several reasons the estimated release may not reliably reflect the release of endogenous compounds. The magnitudes of the release cannot thus be quite correctly estimated using radioactive labels. The basal and K(+)-evoked release of the neuroactive endogenous amino acids γ-aminobutyrate (GABA), glycine, taurine, glutamate and aspartate was now studied in slices from the striatum from 7-day-old to 3-month-old mice under control (normoxic) and ischemic conditions. The release of alanine, threonine and serine was assessed as control. GABA and glutamate release was much greater in 3-month-old than in 7-day-old mice, whereas with taurine the situation was the opposite. Ischemia markedly enhanced the release of all these three amino acids. The release of aspartate and glycine was markedly enhanced as well whereas no effects were discernible in the release of glutamine, alanine, serine and threonine. K(+) stimulation (50 mM) enhanced the release of GABA, glutamate, taurine, aspartate and glycine in most cases, except with taurine in 3-month-old mice under the ischemic conditions and with aspartate in 7-day-old mice under the control conditions. K(+) stimulation did not affect the release of glutamine, alanine, serine or threonine. The results on endogenous amino acids are qualitatively similar to those obtained in our earlier experiments with labeled preloaded amino acids. In conclusion, in developing mice only inhibitory taurine is released in such amounts that may counteract the harmful effects of excitatory amino acids in ischemia.

Increased indoleamine 2,3-dioxygenase (IDO) activity in idiopathic generalized epilepsy.

PURPOSE: Indoleamine 2,3-dioxygenase (IDO) is a cytokine-inducible enzyme that participates in tryptophan (trp) and serotonin metabolism with an ability to modulate neuroinflammation. Several recent studies have shown associations between cytokines and epilepsy. In this study we investigated whether activation of IDO is associated with epilepsy. METHODS: Kynurenine (kyn)/trp serum ratio, as an indicator of IDO activity was analyzed in 271 carefully classified epilepsy patients, and 309 healthy adults. RESULTS: IDO activity was increased in patients with unclassified idiopathic generalized epilepsy (IGE) (n=11; p=0.05), in juvenile myoclonic epilepsy (JME) (n=25; p=0.04) and in patients those with temporal lobe epilepsy but no hippocampal sclerosis (TLE-HS) (n=103; p=0.05) compared to the control subjects. In patients with idiopathic (but not cryptogenic or symptomatic) etiology of epilepsy, IDO activity was increased compared to the control subjects (p<0.05). Patients with extra-TLE or TLE+HS had IDO activity comparable to the control subjects. Patients who were one-month seizure-free prior to sampling had increased IDO activity compared to the control subjects (p=0.03). CONCLUSIONS: Increased IDO activity appeared to be associated with idiopathic generalized epilepsies such as unclassified IGE and JME, two of the most common types of primary generalized epilepsy. We also found a trend of increased IDO activity in patients with TLE-HS. Our results suggest that increased IDO activity may represent an adaptive metabolic phenomenon in epilepsy, which may also have a neuroprotective or anticonvulsive role by downregulating neuroinflammation in the brain.

High activity of indoleamine 2,3-dioxygenase is associated with renal insufficiency in Puumala hantavirus induced nephropathia epidemica.

Nephropathia epidemica (NE) is a hemorrhagic fever with renal syndrome caused by Puumala hantavirus. The severity of NE varies greatly. The aim of the present study was to evaluate whether serum indoleamine 2,3-dioxygenase (IDO) activity is associated with the severity of NE. A prospectively collected cohort of 102 consecutive patients with acute serologically confirmed NE was examined. Serum kynurenine, tryptophan, creatinine, CRP, and blood cell count were measured for up to 5 consecutive days after admission. The kynurenine to tryptophan (kyn/trp) ratio reflecting IDO activity was calculated. A maximum kyn/trp ratio >202 µmol/mmol had a sensitivity of 85% and a specificity of 75% for detecting maximum serum creatinine values >250 µmol/L by receiver operating characteristic (ROC) analysis. A maximum kyn/trp ratio >202 µmol/mmol (high IDO level) was also associated with other parameters reflecting the severity of the disease and renal impairment. Patients with high IDO levels had higher maximum serum creatinine (379 vs. 102 µmol/L, P<0.001), plasma C-reactive protein (104.1 vs. 72.1 mg/L, P=0.029), and blood leukocyte values (11.9 vs. 9.0 × 10(9) /L, P<0.001) compared to patients with kyn/trp ratio ≤ 202 µmol/mmol. They also had lower minimum urinary output (1,100 vs. 1,900 ml/day, P<0.001) and longer hospital stays (8 vs. 5 days, P<0.001). In conclusion, high serum IDO activity was associated with increased disease severity and renal impairment in NE.

Neuroprotection by taurine in ethanol-induced apoptosis in the developing cerebellum.

BACKGROUND: Acute ethanol administration leads to massive apoptotic neurodegeneration in the developing central nervous system. We studied whether taurine is neuroprotective in ethanol-induced apoptosis in the mouse cerebellum during the postnatal period. METHODS: The mice were divided into three groups: ethanol-treated, ethanol+taurine-treated and controls. Ethanol (20% solution) was administered subcutaneously at a total dose of 5 g/kg (2.5 g/kg at time 1 h and 2.5 g/kg at 3 h) to the ethanol and ethanol+taurine groups. The ethanol+taurine group also received two injections of taurine (1 g/kg each, at time zero and at 4 h). To estimate apoptosis, immunostaining for activated caspase-3 and TUNEL staining were made in the mid-sagittal sections containing lobules I-X of the cerebellar vermis at 12 or 8 hours after the first taurine injection. Changes in the blood taurine level were monitored at each hour by reverse-phase high-performance liquid chromatography (HPLC). RESULTS: Ethanol administration induced apoptosis of Purkinje cells on P4 in all cerebellar lobules, most extensively in lobules IX and X, and on P7 increased the number of activated caspase-3-immunoreactive and TUNEL-positive cells in the internal layer of the cerebellum. Administration of taurine significantly decreased the number of activated caspase-3-immunoreactive and TUNEL-positive cells in the internal layer of the cerebellum on P7, but had no effect on Purkinje cells in P4 mice. The high initial taurine concentration in blood of the ethanol+taurine group diminished dramatically during the experiment, not being different at 13 h from that in the controls. CONCLUSIONS: We conclude that the neuroprotective action of taurine is not straightforward and seems to be different in different types of neurons and/or requires prolonged maintenance of the high taurine concentration in blood plasma.

Mechanisms of inhibitory amino acid release in the brain stem under normal and ischemic conditions.

This article deals with the release of GABA, glycine and taurine from the brain stem under normal conditions and in ischemia. The release mechanisms, the effects of glutamate and adenosine receptors, and the roles of nitric oxide and second messengers are reviewed.

Direct exposure to ammonia and hyperammonemia increase the extracellular accumulation and degradation of astroglia-derived glutathione in the rat prefrontal cortex.

We endeavored here to shed light on the supply of glutathione (GSH) precursors from glial cells to neurons and on the interference of ammonia with this process. Administration of ammonium chloride (ammonia) via a microdialysis probe to the rat prefrontal cortex rapidly increased GSH content in the microdialysates. The increase was abrogated by the inhibitor of astrocytic energy metabolism fluoroacetate and the inhibitor of glutathione synthesis buthionine sulfoximine. GSH in the microdialysates was significantly elevated in rats with simple hyperammonemia (HA) or hepatic encephalopathy (HE) (three ip administrations of ammonium acetate or thioacetamide, respectively, at 24-h intervals), only when microdialysis was carried out in the presence of a gamma-glutamyltranspeptidase (gammaGT) inhibitor acivicin. Extracellular GSH increased in cultured rat cortical astrocytes treated with 5mM ammonia for 1 h, but not for 3-72 h, which was the period of increased gammaGT activity. GSH remained increased during the whole 72-h incubation with 5 or 10mM ammonia in C6 glioma cells, where gammaGT activity is intrinsically low and was not increased by ammonia. Collectively, the results suggest that in rats with HA or HE ammonia specifically promote GSH synthesis and export from astrocytes and increase its extracellular degradation, which may improve the availability of precursors for GSH synthesis in neurons and their resistance to ammonia toxicity.