Taurine (2-aminoethanesulfonic acid) deficiency creates a vicious circle promoting obesity

The relation between blood taurine (2-aminoethanesulfonic acid) concentrations and obesity was investigated. Taurine is supplied to the body by dietary ingestion as well as by de novo synthesis; it is anabolized by cysteine dioxygenase (CDO), which is abundantly expressed in liver and white adipose tissue. Overexpression of CDO in 3T3-L1 preadipocytes caused a decrease in the level of cysteine (precursor of taurine) and an increase in the level of taurine in the culture medium, suggesting that CDO is involved in biosynthesis and secretion of taurine in white adipose tissue. In high-fat diet-induced and/or genetically obese mice, a decrease in the blood taurine concentration was observed along with a decrease in CDO expression in adipose tissue but not in liver. Dietary taurine supplementation prevented high-fat diet-induced obesity with increased resting energy expenditure. Thus, taurine deficiency observed in association with obesity may create a vicious circle promoting obesity. Dietary taurine supplementation interrupts this vicious circle and may prevent obesity.

Effect of taurine on gastric oxidative stress and hemorrhagic erosion in brain ischemic rats

The effect of taurine on gastric hemorrhage and mucosal erosion in the brain ischemia (BI) is unknown. The aim of the research was to study the involvement of gastric oxidative stress in hemorrhagic erosion produced in BI rats. The protective effect of taurine on this erosion model was evaluated. Male Wistar rats were deprived of food for 24 h. Under chloral hydrate -anesthesia, bilateral carotid artery ligation (BCAL) was performed 12, 18 and 21 h after removal of food to obtain 12, 6 and 3 h of BI duration. The pylorus and carotid esophagus of rats also were ligated. The stomachs were then irrigated for 3 h with normal saline or simulated gastric juice containing 100 mM HCl plus 17.4 mM pepsin and 54 mM NaCl. The stomach was dissected. Gastric samples were harvested. The rat brain was dissected for examination of ischemia by using triphenyltetrazolium chloride staining method. Changes in gastric ulcerogenic parameters, such as decreased mucosal GSH level as well as enhanced gastric acid back-diffusion, mucosal lipid peroxide generation, histamine concentration, luminal hemoglobin content and mucosal erosion in gastric samples were measured. The results indicated that BCAL could produce severe BI in rats. Moreover, a BI- duration-dependent exacerbation of various ulcerogenic parameters also was observed in these rats. Intraperitoneal taurine (0-300 mg/kg) dose-dependently ameliorated gastric oxidative stress and hemorrhagic erosion in BI rats. Taken together, BI could produce gastric oxidative stress and hemorrhagic erosions that was ameliorated by taurine through stimulation of GSH biosynthesis and inhibition of oxidative stress.

The effects of sulfur amino acid intake on immune function in humans

No direct data exist on the influence of supranormal intakes of sulfur amino acids on immune function in humans. However 3 major products of sulfur amino acids, glutathione (GSH), homocysteine (Hcy), and taurine (Tau), influence, mainly, inflammatory aspects of the immune response in vitro and in vivo. Methionine intakes above approximately 1 g/d transiently raise plasma Tau, Hcy, and GSH. Tau and GSH ameliorate inflammation. Hcy has the opposite effect. A biphasic relation, between cellular GSH and CD4+ and CD8+ numbers occurs in healthy men. How changes in sulfur amino acid intake influence this phenomenon is unknown. In animals, high Tau intakes are antiinflammatory. How immune function in humans is affected is unknown. A positive relation between plasma neopterin (a marker of a Th-1-type immune response) and Hcy indicates that Hcy may play a part in inflammatory aspects of Parkinson's disease and aging. In vitro, Hcy, at concentrations seen following consumption of approximately 6 g L-methionine/d in adults, increases the interactions among T lymphocytes, monocytes, and endothelium. Whether a similar phenomenon occurs in vivo is unknown. Polymorphisms in the methylenetetrahydrofolate reductase gene are associated with raised plasma Hcy in young but not old subjects. The relation of this observation to immune function is unknown. The relationships among Hcy, inflammatory aspects of disease, and in vitro alterations in immune cell behavior create a cautionary note about supplementation of diets with l-methionine to raise intake above approximately 1 g/d. Studies directly linking methionine intake, genetics, plasma Hcy, Tau, and GSH and immune function are needed.

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

Taurine has been proposed to play a role in calcium modulation. To explore the effect of taurine on intracellular calcium homeostasis of isolated cochlear outer hair cells and on the gentamycin-induced inhibition of calcium influx evoked by high K(+) depolarization, we employed fluo-3 imaging of intracellular calcium ([Ca(2+)](i)) via confocal laser scanning microscopy to measure real-time changes of [Ca(2+)](i). We found that the sole application of taurine (5, 10, 20 mM) induced a transient [Ca(2+)](i) increase in a concentration-dependent manner, which was inhibited either by the application of an L-type calcium-channel blocker nifedipine or a calcium-free medium. Pre-incubation with 1mM gentamicin induced inhibition of [C(a)(2+)](i) elevation evoked by high K(+). Short-term (10 min) exposure with a high level of taurine (20 mM) prevented this inhibition. These results indicated that taurine at a high concentration was able to promote calcium influx through L-type calcium channels in isolated outer hair cells and antagonize gentamycin-induced inhibition of calcium elevation evoked by high K(+) by its calcium homeostatic effect.

Nitrogenous compounds of interest in clinical nutrition

The term "conditionally essential" (or semi-essential), initially applied to amino acids, has been generalized to other nutrients. A conditionally essential nutrient is a compound usually produced in adequate amounts by endogenous synthesis but that is exogenously required under certain circumstances. Thus, arginine, glutamine, cysteine, glycine, carnitine, choline, and polyamines are conditionally essential compounds. In addition, dietary nucleotides are considered semi-essential since some rapidly growing tissues such as the gut, bone marrow, and lymphocytes, preferentially use preformed purine and pyrimidine bases for nucleic acid synthesis. This review discusses the study of conditionally essential nitrogenous nutrients of interest in clinical nutrition. Among them we highlight arginine, involved in endothelial, immune, gastrointestinal, and renal functions, in reproduction, neonatal development, wound healing, and tumorigenicity; glutamine, necessary for maintaining bowel integrity, and with beneficial effects on catabolic states such as sepsis, infection, trauma, and cancer; and nucleotides, implicated in cell growth and differentiation, and with various effects on lipid metabolism, intestinal microbiota, and immune system.

The effect of taurine depletion on the contractile properties and fatigue in fast-twitch skeletal muscle of the mouse

Taurine increases force production in skeletal muscle, and taurine levels may fall during exercise. The contractile properties and fatigability of extensor digitorum longus (EDL) muscles depleted of taurine by guanodinoethane sulfonate (GES) treatment were investigated. GES treatment decreased muscle taurine levels to <40% of controls. Peak twitch force levels were 23% of controls in GES treated EDL muscles (p < 0.05), but maximal specific force was unaffected. The force-frequency relationship was examined and significantly less force was produced by the GES treated muscles compared to controls at stimulation frequencies from 50 to 100 Hz (p < 0.05). GES treated EDL muscles exhibited significantly slower rates of fatigue than controls (p < 0.05). In skinned fibres, 20 mM GES had a small but significant effect on force production, indicating that GES may have some minor taurine-like effects. In this study, a fall in taurine levels decreased force output, and increased the endurance of EDL skeletal muscles.

The management of conditioned nutritional requirements in heart failure

Patients suffering from congestive heart failure exhibit impaired myocardial energy production, myocyte calcium overload and increased oxidative stress. Nutritional factors known to be important for myocardial energy production, calcium homeostasis and the reduction of oxidative stress, such as thiamine, riboflavin, pyridoxine, L-carnitine, coenzyme Q10, creatine and taurine are reduced in this patient population. Furthermore, deficiencies of taurine, carnitine, and thiamine are established primary causes of dilated cardiomyopathy. Studies in animals and limited trials in humans have shown that dietary replacement of some of these compounds in heart failure can significantly restore depleted levels and may result in improvement in myocardial structure and function as well as exercise capacity. Larger scale studies examining micronutrient depletion in heart failure patients, and the benefits of dietary replacement need to be performed. At the present time, it is our belief that these conditioned nutritional requirements, if unsatisfied, contribute to myocyte dysfunction and loss; thus, restoration of nutritional deficiencies should be part of the overall therapeutic strategy for patients with congestive heart failure.

Chronic liver disease is triggered by taurine transporter knockout in the mouse

Taurine is an abundant organic osmolyte with antioxidant and immunomodulatory properties. Its role in the pathogenesis of chronic liver disease is unknown. The liver phenotype was studied in taurine transporter knockout (taut-/-) mice. Hepatic taurine levels were ~21, 15 and 6 mumol/g liver wet weight in adult wild-type, heterozygous (taut+/-) and homozygous (taut-/-) mice, respectively. Immunoelectronmicroscopy revealed an almost complete depletion of taurine in Kupffer and sinusoidal endothelial cells, but not in parenchymal cells of (taut-/-) mice. Compared with wild-type mice, (taut-/-) and (taut+/-) mice developed moderate unspecific hepatitis and liver fibrosis with increased frequency of neoplastic lesions beyond 1 year of age. Liver disease in (taut-/-) mice was characterized by hepatocyte apoptosis, activation of the CD95 system, elevated plasma TNF-alpha levels, hepatic stellate cell and oval cell proliferation, and severe mitochondrial abnormalities in liver parenchymal cells. Mitochondrial dysfunction was suggested by a significantly lower respiratory control ratio in isolated mitochondria from (taut-/-) mice. Taut knockout had no effect on taurine-conjugated bile acids in bile; however, the relative amount of cholate-conjugates acid was decreased at the expense of 7-keto-cholate-conjugates. In conclusion, taurine deficiency due to defective taurine transport triggers chronic liver disease, which may involve mitochondrial dysfunction.

Endogenous neuro-protectants in ammonia toxicity in the central nervous system: facts and hypotheses

The paper overviews experimental evidence suggestive of the engagement of three endogenous metabolites: taurine, kynurenic acid, and glutathione (GSH) in the protection of central nervous system (CNS) cells against ammonia toxicity. Intrastriatal administration of taurine via microdialysis probe attenuates ammonia-induced accumulation of extracellular cyclic guanosine monophosphate (cGMP) resulting from over-activation of the N-methyl-D: -aspartate/nitric oxide (NMDA/NO) pathway, and this effect involves agonistic effect of taurine on the GABA-A and glycine receptors. Taurine also counteracts generation of free radicals, increased release of dopamine, and its metabolism to dihydroxyphenylacetic acid (DOPAC). Taurine reduces ammonia-induced increase of cell volume (edema) in cerebrocortical slices by a mechanism involving GABA-A receptors. Massive release of radiolabeled or endogenous taurine from CNS tissues by ammonia in vivo and in vitro is thought to promote its neuroprotective action, by making the amino acid available for interaction with cell membranes and/or by driving excess water out of the CNS cells (astrocytes) that underwent ammonia-induced swelling. Ammonia in vivo and in vitro affects in variable ways the synthesis of kynurenic acid (KYNA). Since KYNA is an endogenous NMDA receptor antagonist with a high affinity towards its glycine site, changes in its content may counter over-activation or depression of glutaminergic transmission observed at the different stages of hyperammonemia. GSH is a major antioxidant in the CNS whose synthesis is partly compartmented between neurons and astrocytes: astrocytic GSH is a source of precursors for the synthesis of neuronal GSH. Ammonia in vitro stimulates GSH synthesis in cultured astrocytes, which may compensate for increased GSH consumption (decreased GSH/GSSG ratio) in neurons.

Taurine-induced modulation of voltage-sensitive Na+ channels in rat dorsal root ganglion neurons

The physiological role of taurine, an abundant free amino acid in the neural system, is still poorly understood. The aim of this study was to investigate its effect on TTX-sensitive (TTX-S) and TTX-resistant (TTX-R) Na+ currents in enzymatically dissociated neurons from rat dorsal root ganglion (DRG) with conventional whole-cell recording manner under voltage-clamp conditions. A TTX-S Na+ current was recorded preferentially from large DRG neurons and a TTX-R Na+ current preferentially from small ones. For TTX-S Na+ channel, taurine of the concentration > or = 10 mM shifted the activation curve in the depolarizing direction and the inactivation curve in the hyperpolarizing direction. There was no change in the activation curve for TTX-R Na+ channel and the inactivation curve was shifted in the hyperpolarizing direction slightly in the presence of taurine > or = 20 mM. When the recovery kinetics was examined, the presence of taurine resulted in a slower recovery from inactivation of TTX-S currents and no change of TTX-R ones. All the effects of taurine were weakly concentration-dependent and partly recovered quite slowly after washout. Our data indicate that taurine alters the properties of Na+ currents in intact DRG neurons. These may contribute to the understanding of taurine as a natural neuroprotectant and the potential of taurine as a useful medicine for the treatment of sensory neuropathies.

Taurine analogues; a new class of therapeutics: retrospect and prospects

Taurine was discovered more than two hundred years ago from animal sources. It is distributed in both mammals and non-mammals and its content is high in several tissues. For more than a century-and-a-half, taurine was regarded just as an end product of sulfur metabolism. Recently, taurine has been rediscovered and its beneficial effects in processes like epilepsy, hypertension, congestive heart failure and diabetes have been well-documented. It was patented and found some clinical utility, but being an amino acid, therapeutic use confronts limitations like restricted permeability and more. This necessitates the development of pro-drugs (analogues) mainly derivatives of taurine. A large number of taurine derivatives have been reported in the literature with partial to marked activity. Taurine derivatives like taltrimide, acamprosate and tauromustine, are already in the market as anti-convulsant, anti-alcoholic and anti-cancer agents. Many other analogues are effective in experimental models. The in depth analysis of these analogues and their biological actions can provide certain clues for further consideration. In the present review, attempts have been made to provide synopsis, synthesis and symbiosis of chemical and biological actions, which may provide future guidance and facilitate further research in this area. The successful journey of these analogues to clinical utility is a healthy and happy sign and an index of bright future, and we hope that this review will provide enough input to ignite the minds.

Taurine increases glucose sensitivity of UCP2-overexpressing beta-cells by ameliorating mitochondrial metabolism

A low-taurine diet during fetal or early postnatal life causes abnormal pancreatic beta-cell development. Tissue and plasma taurine concentrations can also be low in diabetic patients. We examined the effect of taurine on impaired glucose responses in diabetic rat beta-cells adenovirally overexpressing uncoupling protein (UCP)2, which is upregulated in obesity-related type 2 diabetes. We found that taurine pretreatment restored the ATP-to-ADP (ATP/ADP) ratio and glucose-stimulated insulin secretion in UCP2-infected islets. ATP-sensitive K(+) channel sensitivity to dihydroxyacetone, another insulin secretagogue, was similar in both UCP2-infected and control beta-cells. In freshly isolated mitochondria from UCP2-overexpressing insulin-secreting (INS)-1 beta-cells, methyl pyruvate-mediated mitochondrial Ca(2+) increase was significantly ameliorated by taurine. A mitochondrial Ca(2+) uniporter blocker, ruthenium red, inhibited the action of taurine. This study suggests that taurine enhances the glucose sensitivity of UCP2-overexpressing beta-cells, probably by increasing mitochondrial Ca(2+) influx through the Ca(2+) uniporter, thereby enhancing mitochondrial metabolic function and increasing the ATP/ADP ratio.

Taurine-evoked chloride current and its potentiation by intracellular Ca2+ in immature rat hippocampal CA1 neurons

Taurine is one of the most abundant free amino acids in the immature mammalian central nervous system. In the present study, whole-cell patch-clamp recordings were made to examine taurine-evoked currents ( I(Tau)) in acutely dissociated immature rat hippocampal CA1 neurons. Taurine at low concentrations (</=1 mM) activated glycine receptors while at high concentrations (>/=3 mM) activated both glycine and GABA(A) receptors. Moreover, elevation of intracellular Ca(2+) via non-NMDA receptor activation enhanced I(Tau) reversibly. The results indicate that taurine may act as a native ligand of glycine receptors and modulate neurotransmissions in the immature hippocampus, and under certain conditions it can also activate GABA(A) receptors. The potentiation of I(Tau) by intracellular Ca(2+) may contribute to the protection effect of taurine under some cell-damaging conditions.

The role of taurine in cerebral ischemia: studies in transient forebrain ischemia and embolic focal ischemia in rodents

Sudden cessation of blood flow to the brain results in a series of events that either result in rapid loss of brain cells or delayed neuronal injury in certain vulnerable regions of the brain. Research over the last three decades has allowed for a better understanding of how neurons and other brain cells die from the effects of ischemia and hypoxia in the central nervous system. Excitatory and inhibitory neurotransmitters exist in a very precise balance for normal function of the brain. Ischemia very rapidly disrupts this balance resulting in a rapid build-up of excitatory neurotransmitters, especially glutamate in the extracellular space. The increased glutamate together with energy loss opens a number of different types of calcium and sodium channels resulting in the build-up of these ions in neurons, leading to cellular dysfunction and death. While most ischemia research has focused on antagonism of excitatory amino acids, there are some reports on enhancement and amplification of inhibitory responses in focal and global ischemia. The majority of work relates to potentiation of GABA, either endogenous or through GABA potentiating medications. Taurine has neuroinhibitory properties and may also have potential for neuroprotection in cerebral ischemia. This present review focuses on the role of taurine as a neuroprotective agent, possibly acting through several different inhibitory mechanisms. Taurine may inhibit neurotransmitter release and may result in normal intracellular osmolality. In transient global ischemia in gerbils, we studied in vivo microdialysis of amino acids before, during and after ischemia. We were able to show that taurine resulted in attenuation of glutamate during ischemia (however did not reach significance). In similar experiments, neuronal damage was assessed in the hippocampus. Our results show 48% damage in taurine treated animals, 60% in alanine treated animals and 69% in control groups (trend towards protection but again did not reach significance) Focal ischemia was induced by embolizing a thrombus into the distal internal carotid artery and origin of the middle cerebral artery. Again, in studies where we compared taurine to a placebo treated animal, there was no significant decrease in the amount of damage with taurine. There are reports in the literature that taurine may attenuate neuronal injury during ischemia. Our studies in two models of cerebral ischemia in rodents did not reveal neuronal protection. It is possible that higher doses or possibly prolonged use of taurine may show better results. Taurine may also potentially offer additive protective effects when used in combination with thrombolysis or other neuroprotective agents. Further studies are necessary to better understand the potential for taurine as a neuroprotective agent in cerebral ischemia.