Inhibition of hypochlorous acid-mediated reactions by desferrioxamine. Implications for the mechanism of cellular injury by neutrophils

Taurine abates the liver damage induced by γ-irradiation in rats through anti-inflammatory and anti-apoptotic pathways

BACKGROUND

Radiotherapy is the most common regimen for treating human cancers; however, ionizing radiation (IR) has hazardous effects on metabolically active organs such as the liver.

AIM

This study aimed to investigate the possible protective (prophylactic and therapeutic) action of taurine against liver damage induced by gamma irradiation at different time intervals as well as the mechanisms by which taurine could provide its potential amelioration actions.

METHODS

In this study, 90 adult male rats (∼150 g) were randomly divided into five groups. Group 1 is the control group, group 2 received an oral daily dose (500 mg/kg) of taurine for two weeks, group 3 was exposed to a whole-body single dose of γ-irradiation (6 Gy), and groups 4 and 5 received taurine before or after γ-irradiation, respectively. Six rats from each group were sacrificed after 1, 2, and 3 weeks.

RESULTS

Over the period of the 3 weeks studied, there were significant increases in MDA, NO, TNF-α, and cytochrome-c levels and ALT, caspases-9 and -3 activities and significant decreases in GSH, SOD, CAT, and GPx in the irradiated group when compared with the relevant control. The liver of irradiated rats showed dilatation in the central and portal veins, edema, and degenerated hepatocytes.

CONCLUSIONS

Taken together, IR caused maximum devastation in the liver 2 weeks after exposure as shown by elevation of the inflammatory and apoptotic markers and reducing the antioxidants. Taurine was able to alleviate the deleterious biochemical and histological effects whether given before or after IR. The magnitude of the observed protective effects was in both cases very similar.

Role of taurine, its haloamines and its lncRNA TUG1 in both inflammation and cancer progression. On the road to therapeutics? (Review)

For one century, taurine is considered as an end product of sulfur metabolism. In this review, we discuss the beneficial effect of taurine, its haloamines and taurine upregulated gene 1 (TUG1) long non‑coding RNA (lncRNA) in both cancer and inflammation. We outline how taurine or its haloamines (N‑Bromotaurine or N‑Chlorotaurine) can induce robust and efficient responses against inflammatory diseases, providing insight into their molecular mechanisms. We also provide information about the use of taurine as a therapeutic approach to cancer. Taurine can be combined with other chemotherapeutic drugs, not only mediating durable responses in various malignancies, but also circumventing the limitations met from chemotherapeutic drugs, thus improving the therapeutic outcome. Interestingly, the lncRNA TUG1 is regarded as a promising therapeutic approach, which can overcome acquired resistance of cancer cells to selected strategies. In this regard, we can translate basic knowledge about taurine and its TUG1 lncRNA into potential therapeutic options directed against specific oncogenic signaling targets, thereby bridging the gap between bench and bedside.

Taurine provides a time-dependent amelioration of the brain damage induced by γ-irradiation in rats

Exposure to ionizing radiation (IR) is inevitable since over 80% of total average exposure comes from natural sources. Brain is vulnerable to the deleterious effects of IR. Therefore, scientists paid attention in identifying novel compounds to protect against radiation-induced brain injury. Adult male albino rats weighing 120-150 g were divided into five groups, 18 rats each. Group 1 served as control, group 2 received an oral daily dose of taurine (500 mg/kg) for 2 weeks. Group 3 was exposed to a whole body single dose of γ-irradiation (6 Gy). Groups 4 and 5 received taurine before and after γ-irradiation, respectively. Six rats from each group were sacrificed after 1, 2 or 3 weeks. Throughout the 3 weeks studied, there were significant increases in MDA, NO, TNF-α levels, and Cytochrome-c and activities of Caspases -9 and -3 and significant decreases in GSH, SOD, CAT and GPx in the irradiated group when compared with the relevant control. Cerebral cortex of irradiated rats showed vacuolization and nuclear pyknosis in the neuronal cells and focal gliosis. Taurine administration pre- or post-irradiation significantly ameliorated all these previous effects. Taurine had antioxidant, anti-inflammatory, and anti-apoptotic effects and ameliorated the histopathological changes in brain in a time-dependent mode.

Amelioration of Ischemia–Reperfusion Injury in an Isolated Rabbit Lung Model Using OXANOH

Objective: Acute respiratory distress syndrome (ARDS) remains a major cause of morbidity and mortality. Oxygen-free radicals (OFRs) produced during ischemia and reperfusion (IR) have been implicated as the final common pathway in the pathogenesis of this syndrome. Spin traps have been shown to decrease IR injury in several animal lung models. The hydroxylamine, OXANOH (2-ethyl-2,5,5-trimethyl-3-oxazolidine) has been proposed as an ideal spin trap that would trap extra- and intracellular OFRs producing the stable radical, OXANO• (2-ethyl-2,5,5-trimethyl-3-oxazolidinoxyl). Electron microscopy was used to investigate whether OXANOH would protect against IR injury in the rabbit lung. Methods: OXANOH was obtained by hydrogenation of its stable radical, OXANO• using a safe laboratory technique. Several doses of OXANOH were tested to identify a nontoxic dose. Two quantitative methods were used based on the average surface area of the alveoli and average number of alveoli per unit surface area using scanning electron microscopy (SEM). A total of 20 animals were subjected to 2 hours of ischemia followed by 4 hours of reperfusion. On reperfusion, the 4 groups (N = 5) received no treatment, OXANOH, superoxide dismutase (SOD)/catalase, or oxypurinol. Results: A therapeutic dose of 250 μmol/L of OXANO• was suggested in this in vitro model. All the 3 treatments showed significantly less injury compared to the control group and that SOD/catalase was significantly different from OXANOH and oxypurinol ( P < .008). Conclusion: OXANOH ameliorated IR injury in the isolated rabbit lung, almost as effectively as SOD/catalase and oxypurinol.

Ischemia-reperfusion injury in the lung: quantitation using electron microscopy

BACKGROUND

The primary objectives of this study were to determine the time course of ischemia-reperfusion injury in an isolated rabbit lung model and to quantify this damage using electron microscopic methodology coupled with statistical analyses.

MATERIALS AND METHODS

Eight groups of isolated rabbit lungs (n = 5 per group) were subjected to predetermined periods of ischemia-reperfusion. Two hours of ischemia and 4 hours of reperfusion were concluded to be necessary to induce optimal ischemia-reperfusion injury in this model. Four other groups were subjected to 2 hours of ischemia followed by selected periods of reperfusion. These groups were compared to 4 control groups that were perfused for comparable time periods but without the initial ischemia. New quantitative methods were developed based on the average surface area of the alveoli and average number of alveoli per unit surface area, using scanning electron microscopic examination.

RESULTS

Ischemia per se caused substantial damage. Restoration of volume and nutrients reversed this damage at 1 hour of reperfusion, but severe damage was evident at 4 hours of reperfusion, as reported by subjective and blinded examination. By using the new quantitative methods, there was a significant difference between the groups (P < .005) according to the time of post-ischemia-reperfusion, which correlated with the subjective evaluation of damage.

CONCLUSIONS

These 2 new quantitative techniques provide an objective assessment of damage in the isolated rabbit lung model, suggesting that they warrant further consideration in similar studies of ischemia reperfusion injury.

The effect of hypochlorous acid on the expression of adhesion molecules and activation of NF-kappaB in cultured human endothelial cells

Exposure to oxidants can up-regulate the expression of adhesion molecules in endothelial cells with a consequent increase in neutrophil attachment. Similarly, the transcription factor nuclear factor-kappaB (NF-kappaB), which controls the expression of the intercellular adhesion molecules (ICAMs), can also be activated by oxidants in some cells. We have investigated whether hypochlorous acid (HOCl), the major strong oxidant produced by neutrophils, can affect the expression of adhesion molecules on human umbilical vein endothelial cells (HUVEC) and promote neutrophil adhesion. We found that HOCl could induce an increase in neutrophil adhesion to the endothelial cells after 60 min of treatment. Activation of NF-kappaB could be detected under similar conditions. However, the dose of HOCl required for this effect resulted in considerable longer-term toxicity to the cells. Treatment of HUVEC with sublethal doses of HOCl had no effect on NF-kappaB activation, neutrophil adhesion, or the surface expression of E-selectin, ICAM-1, or P-selectin. However, pretreatment with low concentrations of HOCl prevented phorbol myristate acetate-induced von Willebrand factor expression (a marker for P-selectin). These results show that, unlike H(2)O(2), HOCl does not significantly enhance neutrophil attachment to the endothelium. Rather it may be able to inhibit the expression of adhesion molecules with important consequences for endothelial function and inflammatory vascular disease.

Regulation of apoptosis by vitamin C. Specific protection of the apoptotic machinery against exposure to chlorinated oxidants

We have investigated the ability of intracellular vitamin C to protect human umbilical vein endothelial cells from exposure to hypochlorous acid (HOCl) and a range of derived chloramines. Ascorbate provided minimal protection against the cytotoxicity induced by these oxidants, as measured by propidium iodide uptake. In contrast, there was a marked effect on apoptosis, monitored by caspase-3 activation and phosphatidylserine exposure. Extended incubation of the cells with glycine chloramine or histamine chloramine completely blocked apoptosis initiated in the cells by serum withdrawal. This effect was significantly abrogated by ascorbate. Inhibition of apoptosis required the oxidant to be present for an extended period after serum withdrawal and occurred prior to caspase-3 activation. General protection of thiols by ascorbate was not responsible for the protection of apoptosis, because intracellular oxidation by HOCl or chloramines was not prevented in supplemented cells. The results suggest a new role for vitamin C in the regulation of apoptosis. We propose that, by protection of an oxidant-sensitive step in the initiation phase, ascorbate allows apoptosis to proceed in endothelial cells under sustained oxidative stress.

Hypochlorous acid stimulation of the mitogen-activated protein kinase pathway enhances cell survival

We investigated the activation of three subfamilies of mitogen-activated protein kinases (MAP kinase), the extracellular regulated kinase (ERK1/2), p38, and c-Jun N-terminal kinase (JNK), by the myeloperoxidase-derived oxidant HOCl, in human umbilical vein endothelial cells (HUVEC) and human skin fibroblasts. Treatment of fibroblasts with 10-30 microM HOCl induced a dose-dependent increase in the tyrosine phosphorylation of several proteins. ERK1/2 was activated by exposure to sublethal concentrations of reagent HOCl or by HOCl generated by myeloperoxidase as shown by immune complex kinase assays. Maximum activation was seen at 20 microM and peak activation occurred within 10 min. Western blot analysis demonstrated activation of p38 with 30 microM HOCl, occurring at 15-30 min. No activation of JNK was detected in the concentration range investigated. These results show that HOCl is able to activate MAP kinases. Effective doses were considerably lower than with H2O2 and the lack of JNK activation contrasts with the activation frequently seen with H2O2. Exposure to HOCl caused a loss of viability in HUVEC that was markedly enhanced when ERK1/2 activation was inhibited by U0126. This suggests that the activation of ERK promotes cell survival in response to the oxidative challenge.

Fatty acid chlorohydrins and bromohydrins are cytotoxic to human endothelial cells

Reaction of unsaturated lipids with the hypohalous acids (hypochlorous acid and hypobromous acid) results in the addition of the halide (X) across double bonds to form halohydrins (-CH2CH(OH)CH(X)CH2-). These modified lipids could be potentially destabilising to cell membranes due to their increased polarity. We have investigated the effect of pre-formed halohydrins on human umbilical vein endothelial cells (HUVEC) by incubating cultured cells with oleic acid micelles containing chlorohydrins or bromohydrins. Cell detachment and necrotic death were observed with increasing doses of halohydrins, whereas the cells were unaffected by equivalent doses of oleic acid. Bromohydrins caused more lysis than did chlorohydrins at equivalent doses. Complete lysis was seen with 200 microM fatty acid/chlorohydrin micelles and with 50 microM fatty acid/bromohydrin micelles. Chlorohydrin uptake was much less than the oleic acid control whereas bromohydrins were incorporated into the endothelial cells similarly to oleic acid. This difference or the bulkier nature of the bromohydrins could account for their increased toxicity. This study has demonstrated the potential toxicity of the halohydrins, and implications for their formation in inflammation are discussed.

Glutathione oxidation by hypochlorous acid in endothelial cells produces glutathione sulfonamide as a major product but not glutathione disulfide

Treatment of cells with hypochlorous acid (HOCl) at sublethal doses causes a concentration-dependent loss in reduced glutathione (GSH) levels. We have investigated the products of the reaction of HOCl with GSH in human umbilical vein endothelial cells. Despite a complete loss of GSH, there were only very small increases in intracellular and extracellular glutathione disulfide and glutathione sulfonic acid after exposure to HOCl. (35)S labeling of the GSH pool showed only a minimal increase in protein-bound GSH, suggesting that S-thiolation was not a major contributor to HOCl-mediated loss of GSH in endothelial cells. Rather, the products of the reaction were mostly exported from cells and included a peak that co-eluted with the cyclic sulfonamide that is a product of the reaction of GSH with reagent HOCl. Evidence of this species in endothelial cell supernatants after HOCl treatment was also obtained using electrospray mass spectrometry. In conclusion, exposure to HOCl causes the irreversible loss of cellular GSH with the formation of novel products that are rapidly exported from the cell, and resynthesis of GSH will be required to restore levels. The loss of GSH would alter the redox state of the cell and compromise its defenses against further oxidative stress.

Effects of iron and iron chelation in vitro on mucosal oxidant activity in ulcerative colitis

BACKGROUND

Reactive oxygen species may be pathogenic in ulcerative colitis. Oral iron supplements anecdotally exacerbate inflammatory bowel disease and iron levels are elevated in the inflamed mucosa. Mucosal iron may enhance hydroxyl ion production via Fenton chemistry. Conversely, the iron chelator, desferrioxamine, is reportedly beneficial in Crohn's disease.

AIMS

To assess the in vitro effects of exogenous iron and of iron chelators on the production of reactive oxygen species by colonic biopsies from normal control subjects and patients with ulcerative colitis.

METHODS

Luminol-amplified chemiluminescence was used to measure mucosal reactive oxygen species production both before and after addition in vitro of ferric citrate (100 microM), desferrioxamine (1 mM) and 1,10-phenanthroline (1 mM).

RESULTS

Ferric citrate had no effect on the chemiluminescence produced by human colonic mucosa. However, desferrioxamine and phenanthroline reduced chemiluminescence by 47% (n=7, P=0.018) and by 26% (n=10, P=0.005), respectively, in inactive ulcerative colitis, and by 44% (n=9, P=0. 008) and 42% (n=11, P=0.006) in active disease.

CONCLUSION

The lack of effect of ferric citrate suggests that sufficient free iron is already present in inflamed biopsies to drive the Fenton reaction maximally. The effects of desferrioxamine and 1,10-phenanthroline on the chemiluminescence of biopsies from patients with ulcerative colitis suggest that a clinical trial of topical iron chelation in active disease is indicated.

Loss of GSH and thiol enzymes in endothelial cells exposed to sublethal concentrations of hypochlorous acid

We investigated the effect of sublethal concentrations of hypochlorous acid (HOCl) on intracellular thiol groups. Exposure of human umbilical vein endothelial cells to HOCl caused a decrease in cell viability, with concentrations of </=25 microM HOCl being sublethal. At these concentrations, we saw a loss of glutathione and total protein thiol groups. Of the thiol enzymes we investigated, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was particularly susceptible to inactivation, creatine kinase was moderately susceptible, and lactate dehydrogenase was unaffected by HOCl at the concentrations used. Similar results were obtained with HOCl generated over 30 min by myeloperoxidase. GAPDH activity could be regenerated on reincubation of cells in Hanks' balanced salt solution or reduction with dithiothreitol. In contrast, glutathione loss was not reversible, and further decreased with time. Cellular ATP levels decreased with sublethal HOCl concentrations and this appeared to be unrelated to the inactivation of GAPDH. Our results demonstrate that intracellular thiol groups differ in their reactivity with HOCl and suggest that HOCl may be able to regulate specific cellular functions.

Direct evidence of caeruloplasmin antioxidant properties

The chain-breaking antioxidant potential of caeruloplasmin and bovine serum albumin (BSA) has been investigated in comparison with other well-established antioxidants. Their Oxygen Radical Absorbing Capacity (ORAC), was measured by using beta-phycocyanin (beta-PC) as a fluorescent indicator protein, 2,2'-azobis (2-amidinopropane) hydrochloride (AAPH) as a peroxyl radical generator and the water soluble vitamin E analogue, Trolox, as a reference standard. The relative peroxyl absorbing capacities/mole for Trolox, caeruloplasmin, heat-denatured caeruloplasmin (hCP), catalase, bovine serum albumin (BSA), superoxide dismutase (SOD), and deferoxamine were 1; 2.6; 3.3; 3.7; 1.2; 0.1; 0.2, respectively. Caeruloplasmin was far more effective as a peroxyl radical scavenger than SOD, deferoxamine and BSA, but slightly less effective than catalase. The peroxyl radical absorbing capacity of caeruloplasmin was enhanced by heat-denaturation of the protein. Electron paramagnetic resonance (EPR) spectroscopy using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin-trap, was applied in order to measure the scavenger abilities of caeruloplasmin on superoxide radical and hydroxyl radical production and the concentration required to inhibit by 50% oxygen free radical formation (IC50) was determined. The IC50 values of caeruloplasmin, hCP, and BSA for the superoxide radical were 12, 2, 260 microM and for the hydroxyl radical 15, 2, 200 microM. These results show that caeruloplasmin is an effective chain-breaking antioxidant for a variety of radicals, independently of its catalytic ferroxidase activity.

Comparison of human red cell lysis by hypochlorous and hypobromous acids: insights into the mechanism of lysis

Human red blood cells are lysed by the neutrophil-derived oxidant hypochlorous acid (HOCl), although the mechanism of lysis is unknown. Hypobromous acid (HOBr), a similarly reactive oxidant, lysed red cells approx. 10-fold faster than HOCl. Therefore we compared the effects of these oxidants on thiols, membrane lipids and proteins to determine which reactions are associated with lysis. There was no difference in the loss of reduced glutathione or membrane thiols with either oxidant, but HOBr reacted more readily with membrane lipids and proteins. Bromohydrin derivatives of phospholipids and cholesterol were seen at approx. one-tenth the level of oxidant than chlorohydrins were. However, these products were detected only with high concentrations of HOCl or HOBr, which caused instant haemolysis. Membrane protein modification occurred at much lower doses of oxidant and was more closely correlated with lysis. SDS/PAGE analysis showed that band 3, the anion transport protein, was lost at the lowest dose of HOBr and at the higher concentrations of HOCl. Labelling the red cells with eosin 5-maleimide, a fluorescent label for band 3, suggested possible clustering of this protein in oxidant-exposed cells. There was also irreversible cross-linking of all the major membrane proteins; this reaction occurred more readily with HOBr. The results indicate that membrane protein modification is the reaction responsible for HOCl-mediated lysis. These effects, and particularly cross-link formation, might result in clustering of band 3 and other membrane and cytoskeletal proteins to form haemolytic pores.

Oxidation of intracellular glutathione after exposure of human red blood cells to hypochlorous acid

Exposure of human red blood cells to low doses of hypochlorous acid (HOCl) resulted in the loss of intracellular GSH. Oxidation occurred less than 2 min after the addition of HOCl, and required approx. 2.5 mol of HOCl per mol of GSH lost. Loss of GSH preceded oxidation of membrane thiols, the formation of chloramines and haemoglobin oxidation. The susceptibility of intracellular GSH to oxidation by HOCl was two-thirds that of GSH in cell lysates. These results indicate that HOCl can penetrate the red cell membrane, which provides little barrier protection for cytoplasmic components, and that GSH oxidation by HOCl may be a highly selective process. Virtually all of the GSH lost was converted into GSSG. If glucose was added to the medium, most of the GSH oxidized by low doses of HOCl was rapidly regenerated. At higher doses, recovery was less efficient. However, when HOCl was added as a slow infusion rather than in a single bolus, there was increased recovery at higher doses. This indicates that in metabolically active cells regeneration is rapid and GSH may protect cell components from damage by HOCl. HOCl-induced lysis was only slightly delayed by adding glucose to the medium, indicating that lytic injury is not ameliorated by GSH.

Membrane changes associated with lysis of red blood cells by hypochlorous acid

This study was carried out to investigate HOCl-induced lysis of human erythrocytes. Using reagent HOCl with isolated red cells, we showed that the rate of lysis was dependent on the dose of HOCl per red cell rather than on the concentration of oxidant. The process was inhibited by scavengers such as methionine and taurine, but only if they were present at the time of addition of HOCl. Lysis was preceded by a decrease in cell density, a change in the deformability of the membrane as evidenced by ektacytometry, and an increase in K(+)-leak. Electron microscopy showed extensive disruption of the membrane. Increasing doses of HOCl caused progressive loss of membrane thiols, but complete thiol oxidation by N-ethylmaleimide did not result in an equivalent rate of lysis. Restoration of oxidised thiols by incubation with glucose did not significantly alter the pattern of lysis. Taken together, these results suggest that thiol oxidation was not responsible for HOCl-mediated lysis. There was evidence of increasing crosslinking of membrane proteins on electrophoresis, only some of which was due to the formation of disulfides. TLC of the membrane lipids indicated that there may be formation of chlorohydrins by reaction of HOCl with the fatty acid double bonds. This reaction results in the formation of a more polar species which, if formed, would be extremely disrupting to the lipid bilayer. The results indicate that HOCl-mediated damage to the membrane proteins or to the lipid bilayer comprises an initial damaging event that sets the cells on a path toward eventual lysis.

Influence of various compounds on the degradation of hyaluronic acid by a myeloperoxidase system

Myeloperoxidase in the presence of 0.7 mM hydrogen peroxide degrades hyaluronic by a mechanism which involves iron. Degradation is enhanced in the presence of chloride ion, which is attributed to the formation of hypochlorous acid. Myeloperoxidase-dependent degradation of hyaluronic acid is inhibited by superoxide dismutase, desferrioxamine, iodide ion, bromide ion, mannitol, histidine and various antiinflammatory agents. The destructing agent is presumably the hydroxyl radical.

Oxidation of desferrioxamine to nitroxide free radical by activated human neutrophils

Human neutrophils activated by PMA were found to induce the formation of a nitroxide radical from DFO. The presence of SOD was necessary to permit the formation of the DFO radical. The inactive phorbol ester did not induce DFO radical, and DL-sphinganine suppressed the radical produced by the active phorbol ester. Other cell stimuli (Zymocel and the chemotactic peptide) also induced the formation of the DFO radical, although radical concentration was very much lower than with PMA. Participation of NO, OH or 1O2 was ruled out by the inability of NG-methyl-L-arginine, NG-nitro-L-arginine, DMSO, mannitol, histidine, and methionine to inhibit the formation of DFO radical produced by PMA-activated cells. Furthermore, PMA-activated cells did not produce detectable levels of NO2-, a stable oxidation product of NO, and D2O, which enhances the lifetime of singlet oxygen, did not modify the intensity or the lifetime of DFO radical. The involvement of cell MPO was suggested by the inhibition of the DFO radical observed after treatment with catalase or with antihuman MPO antibodies. Also, HOCl was found to induce the DFO radical in cell-free reactions, but our data indicate that the reaction leading to DFO radical formation by neutrophils involves the reduction of MPO compound II back to the active enzyme (ferric-MPO). Anti-inflammatory drugs strongly increased the DFO radical produced by activated neutrophils. On the contrary, none of these drugs was able to increase the DFO radical produced by HOCl. Histidine and methionine that inhibited the DFO radical intensity in cell-free reactions, were shown to act directly on HOCl. Experiments with MPO-H2O2 in SOD- and Cl(-)-free conditions showed the formation of DFO radical and confirmed the hypothesis of the involvement of compound II. The conversion of compound II to ferric MPO by DFO optimized the enzymatic activity of neutrophils, and in the presence of monochlorodimedon (compound II promoting agent) we measured an increased HOCl production. When DFO was modified by conjugation with hydroxyethyl starch, it lost the ability to produce the radical either by neutrophils or by MPO-H2O2 and did not increase HOCl production. The inability of these DFO derivatives to produce potentially toxic species might explain their reported lower toxicity in vivo.