Complexities in the neurotoxic actions of 6-hydroxydopamine in relation to the cytoprotective properties of taurine

The Protective Effect of Taurine on Oxidized Fish-Oil-Induced Liver Oxidative Stress and Intestinal Barrier-Function Impairment in Juvenile Ictalurus punctatus

Dietary lipids provide energy for growth and development and provide fatty acids necessary for normal structure and biological function. However, oxidized lipids cause oxidative stress and intestinal damage. An 8-week feeding trial with fresh fish oil (FFO, control group), oxidized fish oil (OFO), and taurine-supplemented diets (OFOT, OFO + 0.2% of taurine) was conducted to evaluate the protective effect of taurine on oxidized fish-oil-induced liver oxidative stress and intestine impairment in juvenile Ictaluruspunctatus. The results showed that (1) Growth performance was significantly lower in fish fed OFO than in those fed other diets, whereas the opposite occurred in the hepatosomatic index. (2) OFO-feeding significantly increased lipid deposition compared with the FFO group. The addition of taurine ameliorated the OFO-induced increase in lipid vacuolization in the liver, significantly upregulated lpl mRNA expression, and downregulated fas and srebp1 mRNA expression. (3) OFO-feeding significantly reduced oxidative damage of liver. Compared with the OFO group, the OFOT group remarkably upregulated antioxidant enzyme mRNA expression through the Nrf2-Keap1 signaling pathway based on the transcriptional expression. (4) OFO diets induced intestinal physical and immune barrier damage. Compared with the OFO group, OFOT diets remarkably downregulated il-1β, il-6, tnf-α, and il-8 mRNA expression and upregulated tgf-β mRNA expression through the NF-κB signaling pathway. Besides, the addition of taurine to OFO diets significantly upregulated zo-2 and zo-1 mRNA expression, and downregulated claudin-15 and claudin-12 mRNA expression. In conclusion, oxidized-fish-oil diets can cause negative physiological health effects in Ictaluruspunctatus, while adding taurine can increase growth and antioxidant ability, reduce lipid deposition, and improve intestinal health.

Effects of dietary supplementation with taurine on production performance of Angora rabbits

<p>This study aimed to evaluate the effects of dietary supplementation with taurine on production performance, serum biochemistry, immunoglobulin, antioxidant and hormones of Angora rabbits. A total of 160 8-month-old Angora rabbits with similar body weight were randomly assigned to one of four dietary groups, with 40 animals per group. The dietary groups consisted of the following different taurine supplementation levels: 0 (control), 0.1, 0.2, and 0.3% (air-dry basis). The 73-d feeding trial (from July 31 to October 11, 2016 in China) included a 7-d adjustment period and a 66-d experimental period. The results showed that taurine dietary supplementation had effects on feed consumption, hair follicle density and wool yield of the Angora rabbits (<em>P</em>&lt;0.05), and adding 0.2% taurine could improve the wool yield. Compared with the control group, serum total cholesterol and low-density lipoprotein levels in supplemented groups were decreased (<em>P</em>&lt;0.05). Dietary supplementation with taurine could improve the activity of superoxide dismutase, enhance total antioxidant capacity and reduce the content of malondialdehyde in serum (<em>P</em>&lt;0.05). Besides, the serum level of thyroid (T4) hormone and insulin-like growth factor-1 in experimental groups was higher than that in the control group (<em>P</em>&lt;0.05). In conclusion, taurine dietary supplementation could reduce the lipid metabolism, enhance the antioxidant capacity and hormone level of Angora rabbits, and adding 0.2% taurine could achieve the effect of increasing wool production.</p>

The protective effects of taurine on oxidative stress, cytoplasmic free-Ca2+ and apoptosis of pufferfish (Takifugu obscurus) under low temperature stress

The present study was aimed to investigate the low temperature toxicity and its protection by taurine in pufferfish. The experimental basal diets supplemented with taurine at the rates of 250 (control), 550, 850, 1140, 1430, 1740 mg kg^-1 were fed to fish for 8 weeks. The results showed that fish fed diet with taurine had significantly improved weight gain and specific growth rate. After the feeding trial, the fish were then exposed to low temperature stress. The results showed that low temperature stress could induce reactive oxygen species (ROS) generation, disturb the cytoplasm Ca²⁺ homeostasis, and lead to oxidative stress and apoptosis. Compared with the control group, dietary taurine supplementation groups increased antioxidant enzyme genes such as manganese superoxide dismutase (Mn-SOD), glutathione peroxidase (GPx), glutathione reductase (GR) and catalase (CAT), heat shock proteins (HSP70) and complement C3 (C3) mRNA levels under low temperature stress. Meanwhile, dietary taurine supplementation groups reduced ROS generation, and stabilized the cytoplasm Ca²⁺ under low temperature stress. Furthermore, dietary taurine supplementation groups reduced apoptosis via decreasing caspase-3 activity. This is the first report to demonstrate the mechanisms of taurine against low temperature stress in fish.

Mechanism of the protective action of taurine in toxin and drug induced organ pathophysiology and diabetic complications: a review

Taurine (2-aminoethanesulfonic acid), a conditionally essential amino acid, is found in large concentrations in all mammalian tissues and is particularly abundant in aquatic foods. Taurine exhibits membrane stabilizing, osmoregulatory and cytoprotective effects, antioxidative properties, regulates intracellular Ca(2+) concentration, modulates ion movement and neurotransmitters, reduce the levels of pro-inflammatory cytokines in various organs and controls blood pressure. Recently, emerging evidence from the literature shows the effectiveness of taurine as a protective agent against several environmental toxins and drug-induced multiple organ injuries as the outcome of hepatotoxicity, nephrotoxicity, neurotoxicity, testicular toxicity and cardiotoxicity in several animal models. Besides, taurine is also effective in combating diabetes and its associated complications, including cardiomyopathy, nephropathy, neuropathy, retinopathy and atherosclerosis. These beneficial effects appear to be due to the multiple actions of taurine on cellular functions. This review summarizes the mechanism of the prophylactic role of taurine against several environmental toxins and drug-induced organ pathophysiology and diabetes.

Prophylactic and therapeutic effects of taurine against aluminum-induced acute hepatotoxicity in mice

Aluminum is a well known neurotoxin and a possible candidate of hepatotoxins to humans. Using natural antioxidants against metal-induced hepatotoxicity is a modern approach. In the present study, Aluminum (AlCl(3)) intoxication (a single injection of 25mg Al(3+)/kg, i.p.) for 24h in mice resulted in elevations in serum alanine aminotransferase activity and serum tumor necrosis factor and hepatic malondialdehyde levels. Aluminum reduced the activities of glutathione peroxidase, glutathione S-transferase, quinone oxidoreductase, and catalase in liver. In addition, Al caused hepatic hemorrhage, cellular degeneration as well as necrosis of hepatocytes. Ultrastructure examination showed swelling of mitochondria, derangement of rough endoplasmic reticulum cisternae and pleomorphic nuclei with abnormal chromatin distribution. Taurine, a sulfur-containing amino acid was administered to mice daily for 5 days before (at 100mg/kg, i.p.) or 2h after (a single dose of 1g/kg, i.p.) aluminum administration. Treating mice with taurine at either dosing regimens, pre- or post-aluminum administration alleviated aluminum oxidative damaging effects. The rate of recovery was better when taurine was administered prior to Al. Taurine had anaphylactic and therapeutic activity against hepatotoxicity induced by aluminum in mice.

Protective role of taurine against arsenic-induced mitochondria-dependent hepatic apoptosis via the inhibition of PKCdelta-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 NaAsO(2) (2 mg/kg body weight for 6 months) and the hepatic tissue was used for oxidative stress measurements. In addition, the pathophysiologic effect of NaAsO(2) (10 microM) 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 PKCdelta and pre-treatment of hepatocytes with its inhibitor, rottlerin, suppressed the activation of JNK indicating that PKCdelta 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 NaAsO(2) 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 PKCdelta-JNK signalling pathways. Therefore taurine supplementation could provide a new approach for the reduction of hepatic complication due to arsenic poisoning.

Oxidative and nitrosative stress in experimental rat liver fibrosis: Protective effect of taurine

Taurine (TAU) has protective effects on experimental liver fibrosis. The present study investigates whether benefits of TAU are mediated through attenuation of oxidative and nitrosative stresses. Liver fibrosis was induced in male Wistar rats by simultaneous administration of iron (0.5%, w/w) and ethanol (6g/kg/day) for 60 days consecutively. Significant increases in thiobarbituric acid reactive substances (TBARS), lipid hydroperoxides, protein carbonyl content and loss of non-protein, protein and total thiols were observed in the liver of iron plus alcohol-fed rats. Nitrosative stress was marked by increased levels of S-nitrosothiols and decreased nitrite content. Accumulation of nitrated and oxidatively modified proteins in liver was further evidenced by immunohistochemical localization with specific antibodies for 4-hydroxynonenol (4-HNE), 3-nitrotyrosine (3-NT) and dinitrophenol (DNP). Decrease in mitochondrial ion-transport enzymes and disturbances in calcium and iron levels were also observed in these rats. TAU administration (2% (w/v) in drinking water) significantly reduced the levels of lipid hydroperoxides, TBARS, protein carbonyl with concomitant elevation in thiol levels. The presence of 4-HNE, 3-NT and DNP-protein adducts was minimal. TAU also improved mitochondrial enzyme activities and regulated iron and calcium levels. These results show that the restorative effect of taurine in fibrosis involves amelioration of protein and lipid damage by decreasing oxidative and nitrosative stresses.

Mitochondrial damage, cytotoxicity and apoptosis in iron-potentiated alcoholic liver fibrosis: amelioration by taurine

Taurine effectively prevents ischemia-induced apoptosis in the cardiomyocytes and hypothalamic nuclei. The present study explores the influence of taurine on mitochondrial damage, oxidative stress and apoptosis in experimental liver fibrosis. Male albino Wistar rats were divided into six groups and maintained for a period of 60 days as follows: Group I, control; Group II, ethanol treatment [6 g/(kg/day)]; Group III, fibrosis induced by ethanol and iron (0.5% w/w); Group IV, ethanol + iron + taurine (2% w/v); Group V, ethanol + taurine treatment and Group VI, control + taurine treatment. Hepatocytes isolated from ethanol plus iron-treated rats showed decreased cell viability and redox ratio, increased reactive oxygen species formation, lipid peroxidation, DNA fragmentation, and formation of apoptotic bodies. Liver mitochondria showed increased susceptibility to swell, diminished activities of mitochondrial respiratory chain complexes and antioxidants. Taurine administration to fibrotic rats restored mitochondrial function, reduced reactive oxygen species formation, prevented DNA damage, and apoptosis. Thus taurine might contribute to the amelioration of the disease process.

Nephrotoxicity and its prevention by taurine in tamoxifen induced oxidative stress in mice

Tamoxifen (TAM) is an anti-neoplastic drug used for the treatment of breast cancer. It decreases the hexose monophosphate shunt and thereby increasing the incidence of oxidative stress in cells leading to tissue injury. The present study was undertaken to investigate modulatory effects of taurine on the nephrotoxicity of TAM with special reference to protection against disruption of nonenzymatic and enzymatic antioxidants. Oxidative stress was measured by renal lipid peroxidation (LPO) level, protein carbonyl (PC) content, reduced glutathione (GSH), activities of phase I and II drug metabolizing and antioxidant enzymes. TAM treatment resulted in a significant (P < 0.001) increase in LPO in kidney tissues as compared to control, while taurine pretreatment showed a significant decrease (P < 0.01) in the LPO in kidneys when compared with the TAM-treated group. Taurine + TAM group animals showed restoration in the level of cytochrome P450 content, activities of glutathione metabolizing enzymes viz., glutathione-S-transferase, glutathione peroxidase, glutathione reductase, glucose-6-phosphate dehydrogenase. Pretreatment of animals with taurine markedly attenuated, PC content, restored the depleted nonenzymatic and enzymatic antioxidants. These results clearly demonstrate the role of oxidative stress, and suggest a protective effect of taurine on TAM-induced nephrotoxicity in mice.

Changes in CSF composition during heat stress and fever in conscious rabbits

Elevation of brain temperature after stroke can lead to severe brain injury and even a moderate hyperthermia correlates with increased nervous damage. The role of endogenous cryogens in the pathways that down-regulate body temperature are of overwhelming interest in view of their effectiveness in protecting brain from such damage. The aim of the present work was to study whether heat stress (HS) or fever generates brain homeostatic responses aimed at counteracting the resulting rise in body temperature. Conscious rabbits, with cannulas chronically implanted in the cisterna magna and lateral ventricle, underwent HS (50 min, 40 degrees C) or were injected with 25 ng of endogenous pyrogen IL-1beta, while cerebrospinal fluid (CSF) levels of amino acids involved in central mechanisms of thermoregulation like taurine, GABA, aspartate and glutamate were monitored. The concentrations of some CSF cations (Na(+), K(+), Mg(2+) and Ca(2+)) were also determined in view of their purported role (sodium and calcium in particular) in establishing the thermal set point within the hypothalamus. Results show that during HS-induced hyperthermia, CSF taurine and GABA levels were significantly increased. On the contrary, IL-1beta caused an increase in CSF taurine and, concurrently, a decrease in CSF GABA. Aspartate and glutamate did not change in both conditions. Furthermore, among CSF cations, only calcium and sodium underwent changes. In particular, calcium content increased both in HS- and febrile-animals, while CSF sodium decreased significantly only under IL-1beta-injected treatment. In conclusion, GABA and taurine contribute as endogenous cryogens in a different fashion to the central mechanisms, which regulate dissipation of body heat in hyperthermia or heat production in fever, possibly in coordination with extracellular calcium and sodium.

Taurine rescues hippocampal long-term potentiation from ammonia-induced impairment

Hyperammonemia, a major pathophysiological factor in hepatic encephalopathy, impairs long-term potentiation (LTP) of synaptic transmission, a cellular model of learning and memory, in the hippocampus. We have now studied the protective action of taurine on this paradigm by analyzing LTP characteristics in mouse hippocampal slices treated with ammonium chloride (1 mM) in the presence of taurine (1 mM), an ubiquitous osmolyte, antioxidant, and neuromodulator, as well as other substances with such properties. Ammonia-treated slices displayed a significant impairment of LTP maintenance. Taurine and the mitochondrial enhancer l-carnitine, but not the antioxidants (ascorbate, carnosine, and the novel compound GVS-111) or the osmolyte betaine prevented this impairment. The protective effect of taurine was preserved under the blockade of inhibitory GABA(A) and glycine receptors. It is suggested that taurine may rescue the mechanisms of hippocampal synaptic plasticity by improving mitochondrial function under hyperammonemic conditions.

Attenuation of tamoxifen-induced hepatotoxicity by taurine in mice

BACKGROUND

One of the most attractive approaches to disease prevention involves the use of natural antioxidants to protect tissue against toxic injury. We investigated the modulatory effects of exogenously administered taurine on the toxicity of the anticancer drug tamoxifen with special reference to protection against disruption of drug metabolizing and antioxidant enzymes in Swiss albino mice.

METHODS

Male Swiss albino mice were divided into 4 groups. The extent of lipid peroxidation was evaluated in terms of thiobarbituric acid reactive substances formed. The following assays were performed in the hepatic tissue (a) antioxidant enzymes such as superoxide dismutase and catalase, (b) cytochrome P450 content, (c) glutathione-metabolizing enzymes such as glutathione peroxidase, glutathione reductase, glutathione-S-transferase and glucose 6-phosphate dehydrogenase, and (d) low molecular weight antioxidants (reduced glutathione, ascorbic acid) and protein carbonyl content.

RESULTS

Tamoxifen induced lipid peroxidation, protein carbonyl content and inhibited the enzymes of antioxidant defense system. It was also observed that the activities of antioxidant enzymes and glutathione-metabolizing enzymes were considerably stabilized in mice pretreated with taurine.

CONCLUSION

Taurine protects the integrity of the hepatic tissue by stabilizing the reactive oxygen species mediated lipid peroxidation and protein carbonyl formation. Additionally taurine may prove to be efficacious as an antioxidant in tamoxifen-induced hepatotoxicity.

The effect of 6-hydroxydopamine lesions on the release of amino acids in the direct and indirect pathways of the basal ganglia: a dual microdialysis probe analysis

The loss of dopaminergic neurons of the substantia nigra in Parkinson's disease and in animal models of Parkinson's disease is associated with an imbalance in the activity of the so-called 'direct' and 'indirect' pathways of information flow through the basal ganglia. The aim of the present study was to determine whether the imbalance is reflected in changes in the release of GABA, aspartate and glutamate in the pathways using dual probe microdialysis in freely moving rats. Control and 6-hydroxydopamine-(6-OHDA)-lesioned rats were implanted with microdialysis probes in the neostriatum and substantia nigra or globus pallidus and the release of amino acids was analysed in the dialysates. Basal levels of amino acids were largely unaltered by the 6-OHDA lesion; however, the levels of GABA in the globus pallidus dialysates were significantly elevated in the lesioned rats, indicating an imbalance in favour of the indirect pathway. Administration of kainic acid to the neostriatum enhanced the release of GABA locally and in the distal probes in the substantia nigra and globus pallidus. In 6-OHDA-lesioned rats, stimulated release of GABA in the substantia nigra was abolished, indicating a reduction in transmission along the direct pathway. Thus, consistent with the direct-indirect pathway model of the basal ganglia, the 6-OHDA lesion results in an elevation of the basal release of GABA in the striatopallidal (indirect) pathway and a reduction in the evoked release of GABA in the striatonigral (direct) pathway. These imbalances may underlie, at least in part, the motor abnormalities of Parkinson's disease and in animal models of Parkinson's disease.

Interactions of the neurotoxin 6-hydroxydopamine with glyceraldehyde-3-phosphate dehydrogenase

The neurotoxin 6-hydroxydopamine (6-OHDA) oxidised sulphydryl groups in glyceraldenyde-3-phosphate dehydrogenase (GAPDH) with loss of the dehydrogenase activity of the enzyme. 5-Hydroxydopamine behaved similarly at higher concentrations. This oxidation was accompanied by a transient rise in the acyl phosphatase (non-phosphorylating) activity of GAPDH. Treatment with arsenite resulted in loss of the acyl phosphatase activity and restoration of the dehydrogenase activity, consistent with the process involving sulphydryl-group oxidation to the corresponding sulphenate. Prolonged incubation with 6-OHDA resulted in a loss of both enzyme activities. Arsenite was unable to reverse this inhibition, indicating further oxidation, perhaps to sulphinate and sulphonate, to have occurred. RNA, but not DNA, was a partial inhibitor of both the dehydrogenase and acyl phosphatase activities of GAPDH, whereas DNA (both single- and double-stranded) was ineffective. Both single-stranded DNA and RNA inhibited the esterase activity of GAPDH, an activity that requires the absence of NAD+, in a process that was relieved at higher polynucleotide concentrations. Except at very high concentrations (1 mM), treatment of GAPDH 6-OHDA was ineffective at abolishing its to single-stranded DNA. Since GAPDH is an essential enzyme in glycolysis and also plays a role in apoptotic cell death, these results suggest that the effects on this enzyme may contribute to the neurotoxicity of 6-OHDA.