Enhanced taurine release in cultured cerebellar granule cells in cell-damaging conditions

Summary The release of taurine from cultured cerebellar granule neurons was studied in different cell-damaging conditions, including hypoxia, hypoglycemia, ischemia, oxidative stress and in the presence of free radicals. The effects of both ionotropic and metabotropic glutamate receptor agonists on the release were likewise investigated. The release of [³H]taurine from the glutamatergic granule cells was increased by K⁺ (50mM) and veratridine (0.1 mM), the effect of veratridine being the greater. Hypoxia and ischemia produced an initial increase in release compared to normoxia but resulted in a diminished response to K. Hypoglycemia, oxidative stress and free radicals enhanced taurine release, and subsequent K^– treatment exhibited a correspondingly greater stimulation. A common feature of taurine release in all the bove conditions was a slow response to the stimulus evoked by K⁺ and particularly to that evoked by veratridine. All ionotropic glutamate receptor agonists potentiated taurine release, but only the action of kainate seemed to be receptor-mediated. Metabotropic receptor agonists of group I slightly stimulated the release. The prolonged taurine release seen in both normoxia and cell-damaging conditions may be of importance in maintaining homeostasis in the cerebellum and reducing excitability for a longer period than other neuroprotective mechanisms.Abbreviations AIDA (RS)-1-aminoindan-1,5-dicarboxylate - AMPA 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate - CNOX 6-cyano-7-nitroquinoxaline-2,3-dione - DCG IV (2S,2R,3R)-2-(2,3-dicarboxycyclo-propyl)glycine - DHPG (S)-3,5-dihydroxyphenylglycine - EGLU (2S)-2-ethylglutamate - L-AP3 L(+)-2-amino-3-phosphonopropionate - L-AP4 L(+)-2-amino-4-phosphonobutyrate - L-SOP o-phospho-l-serine - NBOX 6-nitro-7-sulphamoyl[f]quinoxaline-2,3-dione - NMDA n-methyl-d-aspartate - trans-ACPD (1S,3S)-1-aminocyclopentane-1,3-dicarboxylate     

Oxidative Stress Induces Persistent Telomeric DNA Damage Responsible for Nuclear Morphology Change in Mammalian Cells

One main function of telomeres is to maintain chromosome and genome stability. The rate of telomere shortening can be accelerated significantly by chemical and physical environmental agents. Reactive oxygen species are a source of oxidative stress and can produce modified bases (mainly 8-oxoG) and single strand breaks anywhere in the genome. The high incidence of guanine residues in telomeric DNA sequences makes the telomere a preferred target for oxidative damage. Our aim in this work is to evaluate whether chromosome instability induced by oxidative stress is related specifically to telomeric damage. We treated human primary fibroblasts (MRC-5) in vitro with hydrogen peroxide (100 and 200 µM) for 1 hr and collected data at several time points. To evaluate the persistence of oxidative stress-induced DNA damage up to 24 hrs after treatment, we analysed telomeric and genomic oxidative damage by qPCR and a modified comet assay, respectively. The results demonstrate that the genomic damage is completely repaired, while the telomeric oxidative damage persists. The analysis of telomere length reveals a significant telomere shortening 48 hrs after treatment, leading us to hypothesise that residual telomere damage could be responsible for the telomere shortening observed. Considering the influence of telomere length modulation on genomic stability, we quantified abnormal nuclear morphologies (Nucleoplasmic Bridges, Nuclear Buds and Micronuclei) and observed an increase of chromosome instability in the same time frame as telomere shortening. At subsequent times (72 and 96 hrs), we observed a restoration of telomere length and a reduction of chromosome instability, leaving us to conjecture a correlation between telomere shortening/dysfunction and chromosome instability. We can conclude that oxidative base damage leads to abnormal nuclear morphologies and that telomere dysfunction is an important contributor to this effect.     

Selective oxidative stress induces dual damage to telomeres and mitochondria in human T cells

Oxidative stress caused by excess reactive oxygen species (ROS) accelerates telomere erosion and mitochondrial injury, leading to impaired cellular functions and cell death. Whether oxidative stress‐mediated telomere erosion induces mitochondrial injury, or vice versa, in human T cells—the major effectors of host adaptive immunity against infection and malignancy—is poorly understood due to the pleiotropic effects of ROS. Here we employed a novel chemoptogenetic tool that selectively produces a single oxygen (¹O₂) only at telomeres or mitochondria in Jurkat T cells. We found that targeted ¹O₂ production at telomeres triggered not only telomeric DNA damage but also mitochondrial dysfunction, resulting in T cell apoptotic death. Conversely, targeted ¹O₂ formation at mitochondria induced not only mitochondrial injury but also telomeric DNA damage, leading to cellular crisis and apoptosis. Targeted oxidative stress at either telomeres or mitochondria increased ROS production, whereas blocking ROS formation during oxidative stress reversed the telomeric injury, mitochondrial dysfunction, and cellular apoptosis. Notably, the X‐ray repair cross‐complementing protein 1 (XRCC1) in the base excision repair (BER) pathway and multiple mitochondrial proteins in other cellular pathways were dysregulated by the targeted oxidative stress. By confining singlet ¹O₂ formation to a single organelle, this study suggests that oxidative stress induces dual injury in T cells via crosstalk between telomeres and mitochondria. Further identification of these oxidation pathways may offer a novel approach to preserve mitochondrial functions, protect telomere integrity, and maintain T cell survival, which can be exploited to combat various immune aging‐associated diseases.     

Experimental evidence for therapeutic potential of taurine in the treatment of nonalcoholic fatty liver disease

The incidence of obesity is now at epidemic proportions and has resulted in the emergence of nonalcoholic fatty liver disease (NAFLD) as a common metabolic disorder that can lead to liver injury and cirrhosis. Excess sucrose and long-chain saturated fatty acids in the diet may play a role in the development and progression of NAFLD. One factor linking sucrose and saturated fatty acids to liver damage is dysfunction of the endoplasmic reticulum (ER). Although there is currently no proven, effective therapy for NAFLD, the amino sulfonic acid taurine is protective against various metabolic disturbances, including alcohol-induced liver damage. The present study was undertaken to evaluate the therapeutic potential of taurine to serve as a preventative treatment for diet-induced NAFLD. We report that taurine significantly mitigated palmitate-mediated caspase-3 activity, cell death, ER stress, and oxidative stress in H4IIE liver cells and primary hepatocytes. In rats fed a high-sucrose diet, dietary taurine supplementation significantly reduced hepatic lipid accumulation, liver injury, inflammation, plasma triglycerides, and insulin levels. The high-sucrose diet resulted in an induction of multiple components of the unfolded protein response in the liver consistent with ER stress, which was ameliorated by taurine supplementation. Treatment of mice with the ER stress-inducing agent tunicamycin resulted in liver injury, unfolded protein response induction, and hepatic lipid accumulation that was significantly ameliorated by dietary supplementation with taurine. Our results indicate that dietary supplementation with taurine offers significant potential as a preventative treatment for NAFLD.     

Attenuation of neointima formation through the inhibition of DNA repair enzyme PARP-1 in balloon-injured rat carotid artery

Increased oxidative stress is a major characteristic of restenosis after angioplasty. The oxidative stress is mainly created by oxidants such as reactive oxygen species (ROS), which are assumed to play an important role in neointima formation after angioplasty. DNA is a sensitive target for oxidants; however, oxidative DNA damage remains a poorly examined field in the pathogenesis of restenosis. In the present study, we demonstrated that the expression of the oxidative DNA damage marker 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxo-dG) was quickly increased in rat carotid arteries after balloon injury. It reached its peak at 14 days after injury and still kept high expression at 28 days after injury. The immunostaining of 8-oxo-dG was present predominantly in the neointima. In response to oxidative DNA damage, the DNA repair enzyme poly(ADP-ribose) polymerase-1 (PARP-1) was significantly increased after balloon injury. The time course change and location of PARP-1 is similar to that of 8-oxo-dG. Daily injections of the PARP-1 inhibitor PJ34 (5 mg.kg(-1).day(-1) ip) attenuated neointima formation by approximately 40% at 7, 14, and 28 days after balloon injury. Treatment with PJ34 inhibited leukocyte infiltration and improved both anatomic (reendothelialization) and functional (endothelial function) recovery of endothelial cells after balloon injury. In conclusion, levels of oxidative DNA damage and the DNA repair enzyme PARP-1 are increased in vessels after balloon injury. Inhibition of PARP-1 attenuates neointima formation through inhibition of leukocyte infiltration and improvement of endothelial cell recovery after balloon injury. Targeting of the DNA repair enzyme might be a therapeutic strategy for restenosis.     

Protective effects of taurine against oxidative stress in the heart of MsrA knockout mice

Taurine has been shown to have potent anti‐oxidant properties under various pathophysiological conditions. We reported previously a cellular dysfunction and mitochondrial damage in cardiac myocytes of methionine sulfoxide reductase A (MsrA) gene knockout mice (MsrA^?/?). In the present study, we have explored the protective effects of taurine against oxidative stress in the heart of MsrA^?/? mice with or without taurine treatment. Cardiac cell contractility and Ca²⁺ dynamics were measured using cell‐based assays and in vivo cardiac function was monitored using high‐resolution echocardiography in the tested animals. Our data have shown that MsrA^?/? mice exhibited a progressive cardiac dysfunction with a significant decrease of ejection fraction (EF) and fraction shortening (FS) at age of 8 months compared to the wild type controls at the same age. However, the dysfunction was corrected in MsrA^?/? mice treated with taurine supplement in the diet for 5 months. We further investigated the cellular mechanism underlying the protective effect of taurine in the heart. Our data indicated that cardiac myocytes from MsrA^?/? mice treated with taurine exhibited an improved cell contraction and could tolerate oxidative stress better. Furthermore, taurine treatment reduced significantly the protein oxidation levels in mitochondria of MsrA^?/? hearts, suggesting an anti‐oxidant effect of taurine in cardiac mitochondria. Our study demonstrates that long‐term treatment of taurine as a diet supplement is beneficial to a heart that is vulnerable to environmental oxidative stresses. J. Cell. Biochem. 113: 3559–3566, 2012. © 2012 Wiley Periodicals, Inc.     

Glutamate-agonist-evoked taurine release from the adult and developing mouse hippocampus in cell-damaging conditions

Summary Taurine is a neuromodulator and osmoregulator in the central nervous system, also protecting neural cells against excitotoxicity. The effects of the ionotropic glutamate receptor agonists N-methyl-D-aspartate (NMDA), kainate and 2-amino-3-hydroxy-5-methyl-4-imidazolepropionate (AMPA) on [³H]taurine release from hippocampal slices from 3-month-old and 7-day-old mice were studied in cell-damaging conditions. Neural cell injury was induced by superfusing the slices in hypoxic, hypoglycemic and ischemic conditions and by exposing them to metabolic poisons, free radicals and oxidative stress. The release of taurine was greatly enhanced in these conditions at both ages, except in oxidative stress. In normal conditions the three glutamate agonists potentiated taurine release in the immature hippocampus in a receptor-mediated manner, but kainate receptors did not participate in the regulation in the adults. The ability of the agonists to evoke taurine release varied in the cell-damaging conditions, but the glutamate-receptor-activated release was generally operating in the immature hippocampus. This glutamate-receptor-evoked massive release of taurine could have significant neuroprotective effects, particularly in the developing hippocampus, countering the harmful actions of the simultaneously liberated excitatory amino acids.     

Accumulation of single-strand breaks is the major cause of telomere shortening in human fibroblasts

Telomere shortening triggers replicative senescence in human fibroblasts. The inability of DNA polymerases to replicate a linear DNA molecule completely (the end replication problem) is one cause of telomere shortening. Other possible causes are the formation of single-stranded overhangs at the end of telomeres and the preferential vulnerability of telomeres to oxidative stress. To elucidate the relative importance of these possibilities, amount and distribution of telomeric single-strand breaks, length of the G-rich overhang, and telomere shortening rate in human MRC-5 fibroblasts were measured. Treatment of nonproliferating cells with hydrogen peroxide increases the sensitivity to S1 nuclease in telomeres preferentially and accelerates their shortening by a corresponding amount as soon as the cells proliferate. A reduction of the activity of intracellular peroxides using the spin trap alpha-phenyl-t-butyl-nitrone reduces the telomere shortening rate and increases the replicative life span. The length of the telomeric single-stranded overhang is independent of DNA damaging stresses, but single-strand breaks accumulate randomly all along the telomere after alkylation. The telomere shortening rate and the rate of replicative aging can be either accelerated or decelerated by a modification of the amount of oxidative stress. Quantitatively, stress-mediated telomere damage contributes most to telomere shortening under standard conditions.     

Cytotoxicity of Malondialdehyde and Cytoprotective Effects of Taurine <Emphasis Type="Italic">via</Emphasis> Oxidative Stress and PGC-1α Signal Pathway in C2C12 Cells

One of the end-products of ROS-induced peroxidation, malondialdehyde (MDA), induces the cross-links in proteins, which leads to perturbation of the physiological functions of cells and contributes to abnormal biological regulation and various disorders. Taurine (2-aminoethanesulfonic acid, Tau) aids in adjusting normal physiological functions to confer stress resistance. The protective effects of Tau against MDA stress in vitro or in vivo were reported previously. In this study, we had investigated the protective effects of taurine on viability, oxidative stress levels and mitochondrial biogenesis in mouse muscle C2C12 cells undergoing MDA induced stress. We show that the treatment with 100 μM MDA leads to increase in cell oxidative stress levels, inhibition of mitochondrial biogenesis and the reduction of the cell survival rates. The pretreatment with 0.1 μM taurine reduced MDA-induced death rate via inhibition of oxidative stress, restoration of mitochondrial functions of the mitochondrial membrane potential (MMP) and ATP production. In MDA stress, the pre-treatment with 0.1 μM taurine leads to upregulation of the factors of mitochondrial biogenesis. These observations suggest that the cytoprotective effects of taurine may be due to an induction of mitochondrial biogenesis.     

Taurine resumed neuronal differentiation in arsenite-treated N2a cells through reducing oxidative stress,endoplasmic reticulum stress,and mitochondrial dysfunction

The goal of the study is to investigate the preventive effect of taurine against arsenite-induced arrest of neuronal differentiation in N2a cells. Our results revealed that taurine reinstated the neurite outgrowth in arsenite-treated N2a cells. Meanwhile, arsenite-induced oxidative stress and mitochondrial dysfunction as well as degradation of mitochondria DNA (mtDNA) were also inhibited by co-treatment of taurine. Since oxidative stress and mitochondrial dysfunction is closely associated with endoplasmic reticulum (ER) stress, we further examined indicators of ER stress, 78 kDa glucose-regulated protein (GRP78), and C/EBP-homologous protein (CHOP) protein expression. The results demonstrated that taurine significantly reduced arsenite-induced ER stress in N2a cells. In the parallel experiment, arsenite-induced disruption of intracellular calcium homeostasis was also ameliorated by taurine. The proven bio-function of taurine preserved a preventive effect against deleteriously cross-talking between oxidative stress, mitochondria, and ER. Overall, the results of the study suggested that taurine reinstated neuronal differentiation by inhibiting oxidative stress, ER stress, and mitochondrial dysfunction in arsenite-treated N2a cells.     

Mechanism underlying the antioxidant activity of taurine: prevention of mitochondrial oxidant production

An important function of the β-amino acid, taurine, is the regulation of oxidative stress. However, taurine is neither a classical scavenger nor a regulator of the antioxidative defenses, leaving uncertain the mechanism underlying the antioxidant activity of taurine. In the present study, the taurine antagonist and taurine transport inhibitor, β-alanine, was used to examine the mechanism underlying the antioxidant activity of taurine. Exposure of isolated cardiomyocytes to medium containing β-alanine for a period of 48?h led to a 45% decrease in taurine content and an increase in mitochondrial oxidative stress, as evidenced by enhanced superoxide generation, the inactivation of the oxidant sensitive enzyme, aconitase, and the oxidation of glutathione. Associated with the increase in oxidative stress was a decline in electron transport activity, with the activities of respiratory chain complexes I and III declining 50–65% and oxygen consumption falling 30%. A reduction in respiratory chain activity coupled with an increase in oxidative stress is commonly caused by the development of a bottleneck in electron transport that leads to the diversion of electrons from the respiratory chain to the acceptor oxygen forming in the process superoxide. Because β-alanine exposure significantly reduces the levels of respiratory chain complex subunits, ND5 and ND6, the bottleneck in electron transport appears to be caused by impaired synthesis of key subunits of the electron transport chain complexes. Co-administration of taurine with β-alanine largely prevents the mitochondrial effects of β-alanine, but treatment of the cells with 5?mM taurine in the absence of β-alanine has no effect on the mitochondria, likely because taurine treatment has little effect on cellular taurine levels. Thus, taurine serves as a regulator of mitochondrial protein synthesis, thereby enhancing electron transport chain activity and protecting the mitochondria against excessive superoxide generation.     

The cytoprotective role of taurine in exercise-induced muscle injury

Summary.  Intense exercise is thought to increase oxidative stress and damage muscle tissue. Taurine is present in high concentration in skeletal muscle and may play a role in cellular defenses against free radical-mediated damage. The aim of this study was to determine if manipulating muscle levels of taurine would alter markers of free radical damage after exercise-induced injury. Adult male Sprague-Dawley rats were supplemented via the drinking water with either 3% (w/v) taurine (n = 10) or the competitive taurine transport inhibitor, β-alanine (n = 10), for one month. Controls (n = 20) drank tap water containing 0.02% taurine and all rats were placed on a taurine free diet. All the rats except one group of sedentary controls (n = 10) were subjected to 90 minutes of downhill treadmill running. Markers of cellular injury and free radical damage were determined along with tissue amino acid content. The 3% taurine treatment raised plasma levels about 2-fold and 3% β-alanine reduced plasma taurine levels about 50%. Taurine supplementation (TS) significantly increased plasma glutamate levels in exercised rats. Exercise reduced plasma methionine levels and taurine prevented its decline. Taurine supplementation increased muscle taurine content significantly in all muscles except the soleus. β-alanine decreased muscle taurine content about 50% in all the muscles examined. Lipid peroxidation (TBARS) was significantly increased by exercise in the extensor digitorium longus (EDL) and gastrocnemius (GAST) muscles. Both taurine and β-alanine completely blocked the increase in TBARs in the EDL, but had no effect in the GAST. Muscle content of the cytosolic enzyme, lactate dehydrogenase (LDH) was significantly decreased by exercise in the GAST muscle and this effect was attenuated by both taurine and β-alanine. Muscle myeloperoxidase (MPO) activity was significantly elevated in the gastrocnemius muscle, but diet had no effect. MPO activity was significantly increased by exercise in the liver and both taurine and β-alanine blocked this effect. There was no effect of either exercise or the diets on MPO activity in the lung or spleen. Running performance as assessed by a subjective rating scale was improved by taurine supplementation and there was a significant loss in body weight in the β-alanine-treated rats 24 hours after exercise. In summary, taurine supplementation or taurine depletion had measurable cytoprotective actions to attenuate exercise-induced injury. Received October 22, 2001 Accepted February 1, 2002     

Regulation of expression of antioxidant enzymes by vitamin E and curcumin in <Emphasis Type="SmallCaps">l</Emphasis>-thyroxine-induced oxidative stress in rat renal cortex

The present study investigates the antioxidative effects of vitamin E and curcumin against l-thyroxine (T₄)-induced oxidative stress in renal cortex of adult male rats. Rats were made hyperthyroid by administration of l-thyroxine (0.0012%) in their drinking water for 30 days. Vitamin E (200 mg/kg body weight/day) and curcumin (30 mg/kg body weight/day) were supplemented singly or in combination orally for 30 days along with l-thyroxine treatment. The elevated level of oxidative stress parameters (lipid peroxidation and protein carbonylation) and decline level of small antioxidant molecules (reduced glutathione and ascorbic acid) in renal cortex of T₄-treated rats were restored back by supplementation of vitamin E or/and curcumin. Increased superoxide dismutase and catalase activities in kidney cortex of T₄-treated rats were ameliorated in response to vitamin E or/and curcumin treatment. The elevated translated product of Cu/Zn-SOD, Mn-SOD and catalase in T₄-treated rats were differentially reduced by the administration of vitamin E and curcumin independently or in combination. Cu/Zn-SOD expression was ameliorated by both vitamin E and curcumin independently or in combination, whereas Mn-SOD expression was ameliorated by the supplementation of vitamin E or curcumin independently. However, the expression of catalase was alleviated by only supplementation of vitamin E to T₄-treated rats. The results suggest that both vitamin E and curcumin may play an important role in protecting T₄-induced oxidative stress in rat renal cortex by differentially modulating the activities of antioxidant enzymes and oxidative stress parameters.     

Balloon injury does not induce heme oxygenase-1 expression, but administration of hemin inhibits neointimal formation in balloon-injured rat carotid artery.

It has been shown that antioxidant agents act inhibitorily against neointimal formation after balloon injury, suggesting the role of oxidative stress as a promotor of intimal cell proliferation. Heme oxygenase-1 (HO-1) is an inducible form of heme catabolizing enzyme that is induced by and acts against oxidative tissue injury. In this set of experiments, we showed that HO-1 was present in newly formed neointima; however, arterial HO-1 expression did not increase in response to balloon injury in rat carotid artery. Intraperitoneal administration of hemin, a HO-1 inducer, for 5 consecutive days resulted in about a 4-fold increase of serum bilirubin concentration. In addition, hemin injection increased HO-1 protein expression in the carotid artery, the heart, the kidney, and the liver. In this condition, balloon injury-induced neointimal formation was markedly inhibited. Local application of tin protoporphyrin, a HO inhibitor, blocked this effect, suggesting that induced HO-1 in the carotid artery was responsible for the inhibition of neointimal formation after balloon injury. This study suggests that induction of the endogenous antioxidant gene can suppress neointimal formation after balloon injury.     

Telomere length assessment: biomarker of chronic oxidative stress?

Telomeres are nucleoprotein structures, located at the ends of chromosomes and are subject to shortening at each cycle of cell division. They prevent chromosomal ends from being recognized as double strand breaks and protect them from end to end fusion and degradation. Telomeres consist of stretches of repetitive DNA with a high G-C content and are reported to be highly sensitive to damage induced by oxidative stress. The resulting DNA strand breaks can be formed either directly or as an intermediate step during the repair of oxidative bases. In contrast to the majority of genomic DNA, there is evidence that telomeric DNA is deficient in the repair of single strand breaks. Since chronic oxidative stress plays a major role in the pathophysiology of several chronic inflammatory diseases, it is hypothesized that telomere length is reducing at a faster rate during oxidative stress. Therefore, assessment of telomere length might be a useful biomarker of disease progression. In this review several features of telomere length regulation, their relation with oxidative stress, and the potential application of measurement of telomere length as biomarker of chronic oxidative stress, will be discussed.     

Improving effect of dietary taurine supplementation on the oxidative stress and lipid levels in the plasma,liver and aorta of rabbits fed on a high-cholesterol diet

The effect of a high-cholesterol diet with or without taurine on lipids and oxidative stress in the plasma, liver and aorta of rabbits was investigated. The animals were maintained on a basal diet (control), a high-cholesterol diet (HC, 1% w/w), or a high- cholesterol diet supplemented with taurine (HCHT, 2.5% w/w) for two months. Taurine has an ameliorating effect on atherosclerosis together with a decreasing effect on the cholesterol and triglyceride levels in rabbits fed on an HC diet. The HCHT diet caused a significant decrease in the malondialdehyde (MDA) and diene conjugate (DC) levels in the plasma, liver and aorta of rabbits as compared to the HC group. This treatment did not alter the antioxidant system in the liver of rabbits in the HC group. Our findings indicate that taurine ameliorated oxidative stress and cholesterol accumulation in the aorta of rabbits fed on the HC diet and that this effect may be related to its antioxidative potential as well as its reducing effect on serum lipids.     

Oxidative damage in telomeric DNA disrupts recognition by TRF1 and TRF2

The ends of linear chromosomes are capped by protein–DNA complexes termed telomeres. Telomere repeat binding factors 1 and 2 (TRF1 and TRF2) bind specifically to duplex telomeric DNA and are critical components of functional telomeres. Consequences of telomere dysfunction include genomic instability, cellular apoptosis or senescence and organismal aging. Mild oxidative stress induces increased erosion and loss of telomeric DNA in human fibroblasts. We performed binding assays to determine whether oxidative DNA damage in telomeric DNA alters the binding activity of TRF1 and TRF2 proteins. Here, we report that a single 8-oxo-guanine lesion in a defined telomeric substrate reduced the percentage of bound TRF1 and TRF2 proteins by at least 50%, compared with undamaged telomeric DNA. More dramatic effects on TRF1 and TRF2 binding were observed with multiple 8-oxo-guanine lesions in the tandem telomeric repeats. Binding was likewise disrupted when certain intermediates of base excision repair were present within the telomeric tract, namely abasic sites or single nucleotide gaps. These studies indicate that oxidative DNA damage may exert deleterious effects on telomeres by disrupting the association of telomere-maintenance proteins TRF1 and TRF2.     

Protective Role of Taurine against Arsenic-Induced Mitochondria-Dependent Hepatic Apoptosis via the Inhibition of PKCδ-JNK Pathway

Background

Oxidative stress-mediated hepatotoxic effect of arsenic (As) is mainly due to the depletion of glutathione (GSH) in liver. Taurine, on the other hand, enhances intracellular production of GSH. Little is known about the mechanism of the beneficial role of taurine in As-induced hepatic pathophysiology. Therefore, in the present study we investigated its beneficial role in As-induced hepatic cell death via mitochondria-mediated pathway.

Methodology/Principal Findings

Rats were exposed to NaAsO₂ (2 mg/kg body weight for 6 months) and the hepatic tissue was used for oxidative stress measurements. In addition, the pathophysiologic effect of NaAsO₂ (10 µM) on hepatocytes was evaluated by determining cell viability, mitochondrial membrane potential and ROS generation. As caused mitochondrial injury by increased oxidative stress and reciprocal regulation of Bcl-2, Bcl-xL/Bad, Bax, Bim in association with increased level of Apaf-1, activation of caspase 9/3, cleavage of PARP protein and ultimately led to apoptotic cell death. In addition, As markedly increased JNK and p38 phosphorylation with minimal disturbance of ERK. Pre-exposure of hepatocytes to a JNK inhibitor SP600125 prevented As-induced caspase-3 activation, ROS production and loss in cell viability. Pre-exposure of hepatocytes to a p38 inhibitor SB2035, on the other hand, had practically no effect on these events. Besides, As activated PKCδ and pre-treatment of hepatocytes with its inhibitor, rottlerin, suppressed the activation of JNK indicating that PKCδ is involved in As-induced JNK activation and mitochondrial dependent apoptosis. Oral administration of taurine (50 mg/kg body weight for 2 weeks) both pre and post to NaAsO₂ exposure or incubation of the hepatocytes with taurine (25 mM) were found to be effective in counteracting As-induced oxidative stress and apoptosis.

Conclusions/Significance

Results indicate that taurine treatment improved As-induced hepatic damages by inhibiting PKCδ-JNK signalling pathways. Therefore taurine supplementation could provide a new approach for the reduction of hepatic complication due to arsenic poisoning.     

Glutamate receptor-mediated taurine release from the hippocampus during oxidative stress

Background

Hippocampal slices swell and release taurine during oxidative stress. The influence of cellular signalling pathways on this process is unclear. Glutamate signalling can facilitate volume regulation in other CNS preparations. Therefore, we hypothesize activation of taurine release by oxidative stress results from tissue swelling and is coupled to activation of glutamate receptors.

Methods

Rat hippocampi were incubated at room temperature for 2 hr in artificial cerebrospinal fluid (aCSF) equilibrated with 95% O₂ plus 5% CO₂. For some slices, 1 mM taurine was added to the aCSF to maintain normal tissue taurine content. Slices then were perfused with aCSF at 35° C and baseline data recorded before 2 mM H₂O₂ was added. For some studies, mannitol or inhibitors of glutamate receptors or the volume-regulated anion channel (VRAC) were added before and during H₂O₂ treatment. The intensity of light transmitted through the slice (the intrinsic optical signal, IOS) was determined at 1-min intervals. Samples of perfusate were collected at 2-min intervals and amino acid contents determined by HPLC. Data were analyzed by repeated measures ANOVA and post hoc Dunnett’s test with significance indicated for p<0.05.

Results

IOS of slices prepared without taurine treatment increased significantly by 3.3±1.3% (mean±SEM) during oxidative stress. Little taurine was detected in the perfusate of these slices and the rate of taurine efflux did not change during H₂O₂ exposure. The α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate antagonist, 25 µM CNQX, but not the N-methyl-D-aspartate (NMDA) receptor antagonist, 10 µM MK-801, inhibited the increase in IOS during H₂O₂ treatment. Taurine-treated slices exposed to H₂O₂ showed no change in IOS; however, taurine efflux increased by 335±178%. When these slices were perfused with hypertonic aCSF (350 mOsm) or exposed to the VRAC inhibitor, 20 µM DCPIB, no increase in the taurine efflux rate was observed during H₂O₂ exposure. Taurine-treated slices perfused with 10 µM MK-801 during H₂O₂ exposure showed a 4.6±1.9% increase in IOS but no increase in the taurine efflux rate.

Conclusions

Taurine efflux via VRAC is critical for volume regulation of hippocampal slices exposed to oxidative stress. This increased taurine efflux does not result from direct activation of the taurine release pathway by H₂O₂. NMDA receptor activation plays an important role in taurine release during oxidative stress.