Protective Effect Of Dithiothreitol Research Articles

Effect of thiosulphinates contained in garlic extract on growth, proton fluxes and membrane potential in maize (Zea mays L.) coleoptile segments

The effect of thiosulphinates contained in garlic extract (GE) on endogenous growth, growth in the presence of either indoleacetic acid (IAA) or fusicoccin (FC), and proton extrusion in maize coleoptile segments were studied. In addition, membrane potential changes at some GE dilutions and the protective effect of dithiothreitol (DTT) against GE toxicity were also determined. It was found that GE at almost all dilutions studied, when added to the incubation medium inhibited endogenous growth as well as growth in the presence of either IAA or FC. Simultaneous measurements of growth and external pH indicated that the administration of GE resulted in a complex change in the pH of the external medium; after an initial transient acidification, pH increased and reached the maximal value followed by a gradual decrease of medium pH. When IAA or FC was added after preincubation of the segments in the presence of GE the changes in medium pH were not significantly different from these obtained with GE only. If the coleoptile segments were first preincubated with GE and subsequently GE was removed, the addition of IAA induced strong growth and medium acidification. Dithiothreitol added together with GE neutralized the toxic effect of GE on growth of coleoptile segments incubated in the presence of IAA. The addition of GE to the control medium caused a depolarization of the membrane potential, the value of witch depended on GE dilution. These results indicate that the toxic effect of GE on growth of plant cells might be caused by disruption of the catalytic function of the plasma membrane H+-ATPase on formation of the disulfide bonds.

Spectroscopic and Microscopic Studies on the Mechanisms of Mitochondrial Toxicity Induced by Different Concentrations of Cadmium

The deleterious action of Cd2+ on rat liver mitochondria was investigated in this work using spectroscopic and microscopic methods. The concentration dependence of Cd2+ on mitochondrial swelling, membrane potential and membrane fluidity was studied. Our aim was to detect the active sites of Cd2+ in the mitochondrial membrane treatments with cyclosporin A (CsA) and EGTA on the mitochondrial permeability transition (MPT) induced by low and high concentrations of Cd2+. The protective effects of dithiothreitol, human serum albumin and monobromobimane+ on Cd2+-induced MPT were also monitored. All of these investigations indicated that Cd2+ can directly affect MPT at two separate localization sites at different concentrations: the classic Ca2+ triggering site and the thiol (-SH) groups of membrane proteins matched by MPT pore opening (defined as "S" site). At the high concentration of Cd2+, other free -SH groups in the mitochondrial matrix may be involved in this process. These findings were supported by transmission electron microscopy and shed light on the toxic mechanism of Cd2+ on mitochondria.

Effects of Mercury on the Isolated Heart Muscle Are Prevented by DTT and Cysteine

The protective effects of dithiothreitol (DTT, 50 μM) and cysteine (CYS, 100 μM) against toxic effects of HgCl2(1, 2.5, 5, and 10 μM) were studied in isolated, isometrically contracting rat papillary muscles. Force reduction promoted by Hg2+was prevented by both DTT and CYS. Also, after both treatments, no significant changes in dF/dt were observed. A progressive reduction in the time to peak tension was observed when increased concentrations of HgCl2were used after CYS and DTT treatment. This was an indication that the enhancement of calcium release from the sarcoplasmic reticulum produced by mercury was not affected by DTT and CYS. Tetanic contractions were also studied. After treatment with DTT or CYS tetanic tension did not change. No significant reduction of tetanic tension was observed during treatment with 1 μM Hg2+but its reduction was observed after 5 μM Hg2+. Myosin ATPase activity was also affect by Hg2+, being completely blocked by 1 μM Hg2+and reduced by 50% with 0.15 μM Hg2+. Full activity was restored by using 500 nM DTT. These findings suggest that several but not all toxic effects of Hg2+on the mechanical activity of the heart muscle are prevented by protectors of SH groups such as DTT and CYS. The enhancement of the Ca2+release from the sarcoplasmic reticulum by Hg2+during activation was not affected by prior treatment with DTT and CYS, suggesting that interactions with SH groups may not be important for the activation of the Ca2+channel of the sarcoplasmic reticulum.

Ca2+-Independent Permeabilization of the Inner Mitochondrial Membrane by Peroxynitrite Is Mediated by Membrane Protein Thiol Cross-Linking and Lipid Peroxidation

Peroxynitrite anion, the reaction product of superoxide and nitric oxide, is a potent biological oxidant, which inactivates mammalian heart mitochondrial NADH–coenzyme Q reductase (complex I), succinate dehydrogenase (complex II), and ATPase, without affecting cytochrome c oxidase (complex IV). In this paper, we evaluated the effect of peroxynitrite on mitochondrial membrane integrity and permeability under low calcium concentration. Phosphate buffer was used in most of our experiments since Hepes, Tris, mannitol, and sucrose were found to inhibit the oxidative chemistry of peroxynitrite. Peroxynitrite (0.1–1.0 mm) caused a dose-dependent decrease in the ability of mitochondria to build up a membrane potential whenN,N,N′,N′-tetramethyl-p-phenylenediamine/ascorbate were used as substrate. Elimination of the membrane potential was accompanied by penetration of the osmotic support (KCl/NaCl) into the matrix as judged by the parallel occurrence of mitochondrial swelling. This swelling was partially inhibited by dithiothreitol (DTT) or butylated hydroxytoluene (BHT) and was insensitive to ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid, ADP, and cyclosporin A. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis of solubilized membrane proteins indicated that alterations in membrane permeability were associated with the production of protein aggregates due to membrane protein thiol cross-linking. The protective effect of DTT on both mitochondrial swelling and protein polymerization suggests the involvement of disulfide bonds in the membrane permeabilization process. In addition, the increase in thiobarbituric acid-reactive substances and the partial inhibitory effect of BHT indicate the occurrence of lipid peroxidation. These results support the idea that under our experimental conditions peroxynitrite causes mitochondrial structural and functional alterations by Ca2+-independent mechanisms through lipid peroxidation and protein sulfhydryl oxidation.

クロロタロニルによるラット肝細胞毒性に対するジチオスレイトールの防御効果

クロロタロニルによるラット肝細胞毒性に対するジチオスレイトールの防御効果

Amelioration of cisplatin toxicity in rat renal cortical slices by dithiothreitol in vitro.

1. The protective effects of dithiothreitol (DTT) on cisplatin-induced nephrotoxicity were investigated with rat renal cortical slices. 2. The nephrotoxic effects of cisplatin (2 mmol l-1) were manifested in several ways: the Na+ and water content were increased while K+ was decreased. The malondialdehyde (MDA) concentration in the slices and the lactate dehydrogenase (LDH) released into the medium were increased. The uptake of p-aminohippurate (PAH), the synthesis of glucose and the glutathione (GSH) concentration in the slices were all decreased. 3. Despite a DTT-related increase in platinum (Pt) uptake by the slices, DTT (0.5-2 mmol l-1) ameliorated all these toxic effects of cisplatin in a concentration related manner. 4. The results suggest that the protective mechanism of DTT is its antioxidative action. DTT is also a metal chelator, however, and so a protective effect via chelation of Pt by DTT cannot be excluded.

Dithiothreitol reversal of allyl alcohol cytotoxicity in isolated rat hepatocytes

Reversal by dithiothreitol (DTT) of allyl alcohol cytotoxicity was investigated in isolated rat hepatocytes. Allyl alcohol-induced protein sulfhydryl loss, bleb formation, and cell death were prevented by DTT, when it was added to hepatocytes 30 min after the toxicant. The protective effect of DTT also was demonstrated in cells that were washed after 30 min of exposure to allyl alcohol, indicating that protection was not related to inhibition of allyl alcohol metabolism or inactivation of acrolein. DTT reversed the cell surface protrusions that formed during exposure to allyl alcohol, but reversal of blebbing did not insure that the cells would remain viable. Glutathione disulfide was not formed in allyl alcohol-treated cells, and DTT reversal of cytotoxicity occured without restoring glutathione levels. Moreover, protection against allyl alcohol toxicity required the continuous presence of DTT. The results suggest that initial events in the toxic process are reversible, and that DTT can prevent cytotoxicity if added to hepatocytes before irreversible damage occurs; however, the mechanism by which DTT exerts its protection is not clear.

Modification of contractile proteins by oxygen free radicals in rat heart.

This study was undertaken to investigate the effects of oxygen free radicals on myofibrillar creatine kinase activity. Isolated rat heart myofibrils were incubated with xanthine+xanthine oxidase (a superoxide anion radical-generating system) or hydrogen peroxide and assayed for creatine kinase activity. To clarify the involvement of changes in sulfhydryl groups in causing alterations in myofibrillar creatine kinase activity, 1) effects of N-ethylmaleimide (sulfhydryl groups reagent) on myofibrillar creatine kinase activity, 2) effects of oxygen free radicals on myofibrillar sulfhydryl groups content, and 3) protective effects of dithiothreitol (sulfhydryl groups-reducing agent) on the changes in myofibrillar creatine kinase activity due to oxygen free radicals were also studied. Xanthine+xanthine oxidase inhibited creatine kinase activity both in a time- and a concentration-dependent manner. Superoxide dismutase (SOD) showed a protective effect on the depression in creatine kinase activity caused by xanthine+xanthine oxidase. Hydrogen peroxide inhibited creatine kinase activity in a concentration-dependent manner; this inhibition was prevented by the addition of catalase. N-ethylmaleimide reduced creatine kinase activity in a dose-dependent manner. The content of myofibrillar sulfhydryl groups was decreased by xanthine+xanthine oxidase; this reduction was prevented by SOD. Furthermore, the depression in myofibrillar creatine kinase activity by xanthine+xanthine oxidase was protected by the addition of dithiothreitol. Oxygen free radicals may inhibit myofibrillar creatine kinase activity by modifying sulfhydryl groups in the enzyme protein. The reduction of myofibrillar creatine kinase activity may lead to a disturbance of energy utilization in the heart and may contribute to cardiac dysfunction due to oxygen free radicals.

Methylene blue decreases the functional activity of alpha-1-protease inhibitor in bronchoalveolar lavage.

Methylene blue, used as an external marker for bronchoalveolar lavage (BAL) in a concentration of 1 microgram/ml, reduced the functional activity of BAL alpha 1-protease inhibitor (alpha 1-PI) in 2 healing nonsmokers who each had 2 BAL done, one with and the other without methylene blue. Inactivation of alpha 1-PI by methylene blue was confirmed by in vitro experiments on diluted serum and concentrated BAL incubated with methylene blue. Inactivation of alpha 1-PI is likely due to its oxidation by methylene blue, as suggested by the in vitro protective effect of dithiothreitol, a reducing agent. These observations indicate a need for caution when considering the use of methylene blue as an external marker for bronchoalveolar lavage.

Protective effects of dithiothreitol on cadmium-induced injury in isolated rat hepatocytes

The biochemical mechanism involved in cadmium-induced cellular injury remains to be elucidated. Various theories have been proposed to account for this action, one of which is an interaction with reduced sulfhydryl (SH) groups of membranes. The ability of a known SH group reducing agent, dithiothreitol (DTT), to interact with cadmium-induced damage to isolated hepatocytes was investigated. Cadmium chloride produced a cytotoxic response similar to that previously demonstrated. When added just prior to cadmium chloride, DTT was found to protect against the metal-induced injury. If the cells were first exposed to cadmium for 15 min before DTT was added, it was found that the cells could be rescued from the ensuing expression of toxicity due to cadmium. This result was regardless of the fact that by 15 min the cells had accumulated a quantity of cadmium that was associated with cell injury. Furthermore, DTT did not exert its action by decreasing the amount of cadmium accumulation by the cells. Under some experimental conditions, an increased cadmium uptake in the presence of DTT was observed. While it is not clear as to whether the chelating or thiol reductive properties of DTT are of prime importance in the demonstrated protection, the data show that toxicity is not due to a simple, single irreversible interaction between cadmium and membrane SH groups.