Preparation of labeled staphylococcal enterotoxin A with high specific activity.
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Staphylococcal enterotoxin A (SEA) was labeled by the chloramine-T method with 125I to a specific activity of 68 to 300 muCi per mug of SEA and with 131I to specific activity of 8 to 218 muCi per mug of SEA. SEA was partially damaged and aggregated during the labeling and storage. The damage seemed not to be greatly dependent on the specific activity of labeled entertoxin. Crossed immunoelectrophoresis showed two antigenically active and three inactive components in the ascending part of the labeled enterotoxin peak during fractionation by gel chromatography. During storage at 4 degrees C, the antigenic activity of label decreased faster when labeling had been with 131I than when with 125I. The antigenic activity of labeled SEA was lowered remarkably in the ascending part of the protein peak. Greatest release of radioiodine during storage was in the same part of protein peak. According to these results, the most suitable label for radioimmunoassay is obtained from the descending part of protein peak. (+info)
Secondary radicals derived from chloramines of apolipoprotein B-100 contribute to HOCl-induced lipid peroxidation of low-density lipoproteins.
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Oxidation of low-density lipoproteins (LDL) is thought to contribute to atherogenesis. Although there is increasing evidence for a role of myeloperoxidase-derived oxidants such as hypochlorite (HOCl), the mechanism by which HOCl modifies LDL remains controversial. Some studies report the protein component to be the major site of attack, whereas others describe extensive lipid peroxidation. The present study addresses this controversy. The results obtained are consistent with the hypothesis that radical-induced oxidation of LDL's lipids by HOCl is a secondary reaction, with most HOCl consumed via rapid, non-radical reaction with apolipoprotein B-100. Subsequent incubation of HOCl-treated LDL gives rise to lipid peroxidation and antioxidant consumption in a time-dependent manner. Similarly, with myeloperoxidase/H2O2/Cl- (the source of HOCl in vivo), protein oxidation is rapid and followed by an extended period of lipid peroxidation during which further protein oxidation does not occur. The secondary lipid peroxidation process involves EPR-detectable radicals, is attenuated by a radical trap or treatment of HOCl-oxidized LDL with methionine, and occurs less rapidly when the lipoprotein was depleted of alpha-tocopherol. The initial reaction of low concentrations of HOCl (400-fold or 800-fold molar excess) with LDL therefore seems to occur primarily by two-electron reactions with side-chain sites on apolipoprotein B-100. Some of the initial reaction products, identified as lysine-residue-derived chloramines, subsequently undergo homolytic (one-electron) reactions to give radicals that initiate antioxidant consumption and lipid oxidation via tocopherol-mediated peroxidation. The identification of these chloramines, and the radicals derived from them, as initiating agents in LDL lipid peroxidation offers potential new targets for antioxidative therapy in atherogenesis. (+info)
Hypochlorite-induced oxidation of proteins in plasma: formation of chloramines and nitrogen-centred radicals and their role in protein fragmentation.
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Activated phagocyte cells generate hypochlorite (HOCl) via the release of H2O2 and the enzyme myeloperoxidase. Plasma proteins are major targets for HOCl, although little information is available about the mechanism(s) of oxidation. In this study the reaction of HOCl (at least 50 microM) with diluted fresh human plasma has been shown to generate material that oxidizes 5-thio-2-nitrobenzoic acid; these oxidants are believed to be chloramines formed from the reaction of HOCl with protein amine groups. Chloramines have also been detected with isolated plasma proteins treated with HOCl. In both cases chloramine formation accounts for approx. 20-30% of the added HOCl. These chloramines decompose in a time-dependent manner when incubated at 20 or 37 degrees C but not at 4 degrees C. Ascorbate and urate remove these chloramines in a time- and concentration-dependent manner, with the former being more efficient. The reaction of fresh diluted plasma with HOCl also gives rise to protein-derived nitrogen-centred radicals in a time- and HOCl-concentration-dependent manner; these have been detected by EPR spin trapping. Identical radicals have been detected with isolated HOCl-treated plasma proteins. Radical formation was inhibited by excess methionine, implicating protein-derived chloramines (probably from lysine side chains) as the radical source. Plasma protein fragmentation occurs in a time- and HOCl-concentration-dependent manner, as evidenced by the increased mobility of the EPR spin adducts, the detection of further radical species believed to be intermediates in protein degradation and the loss of the parent protein bands on SDS/PAGE. Fragmentation can be inhibited by methionine and other agents (ascorbate, urate, Trolox C or GSH) capable of removing chloramines and reactive radicals. These results are consistent with protein-derived chloramines, and the radicals derived from them, as contributing agents in HOCl-induced plasma protein oxidation. (+info)
Chloramine-induced haemolysis presenting as erythropoietin resistance.
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BACKGROUND: In December 1996 we identified an outbreak of erythropoietin (rHuEpo) resistance requiring a substantial increase in rHuEpo dosage in one of our four haemodialysis (HD) units. The dialysate chloramine levels in this unit had risen from <0.1 p.p.m. in 1996 to 0.25-0.3 p.p.m. in 1997. In the other three HD units levels remained <0.1 p.p.m. Other parameters of water quality were within accepted standards. METHODS: Monthly records of haemoglobin level and rHuEpo dose were available for 148 patients between January 1996 and May 1998. Seventy-two patients, with no recognized cause of rHuEpo resistance, were analysed in detail (August 1997 to April 1998). A subgroup of 15 patients was examined for evidence of haemolysis during HD (methaemoglobin and haptoglobin levels, reticulocyte counts and Heinz bodies). Larger carbon columns were installed in December 1997 to effect chloramine removal. RESULTS: There was an increase in mean methaemoglobinaemia of 23% (P<0.01) and a 21% fall in mean haptoglobin (P<0.01) across HD, although no patient had a reticulocytosis and only one patient with G6PD deficiency had Heinz bodies. Following installation of larger carbon columns there was an 18.6% rise (P<0.001) in mean haemoglobin level and a subsequent 25.0% reduction (P<0.001) in mean rHuEpo dose. Intradialytic changes in methaemoglobin and haptoglobin were abolished. The dialysate chloramine levels fell to < 0.1 p.p.m. Water company records subsequently revealed a sustained twofold increase in mains water chloramine from November 1996. CONCLUSIONS: This is the first report linking chloramine exposure and rHuEpo resistance, with only subtle signs of haemolysis. Unheralded changes in mains water constituents can directly affect dialysate water quality and clinical outcomes. (+info)
Natural antioxidant, chlorogenic acid, protects against DNA breakage caused by monochloramine.
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Chlorogenic acid prevented a stepwise conversion of plasmid pUC18 DNA, from I-->form II-->form III, induced by 3 mM monochloramine with a half inhibition of 67.4 microM. Chlorogenic acid reacted with monochloramine in a time-dependent manner, and the reaction rate increased with decreasing pH. These results suggest that chlorogenic acid prevents genotoxicity of monochloramine in gastric mucosa. (+info)
Monochloramine enhances Fas (APO-1/CD95)-induced apoptosis in Jurkat T cells.
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Monochloramine derivatives are physiological oxidants produced by activated neutrophils. We report the effects of chemically prepared monochloramine (NH2Cl) on Fas-induced apoptosis in Jurkat T cells. When the cells were pretreated with NH2Cl (20-70 microM), subsequent addition of apoptosis-inducing anti-Fas antibody resulted in a synergistic enhancement of apoptosis. Treatment of NH2Cl (50-70 microM) alone resulted in a slight but definite apoptosis. Caspase activities, as measured by DEVD and IETD cleavage activities, were also elevated synergistically by NH2Cl + anti-Fas antibody stimulation. Moreover, a broad caspase inhibitor, Z-VAD-fmk, almost completely inhibited the apoptosis induced by NH2Cl and/or anti-Fas antibody. Fas expression on the Jurkat cell surface was not affected by the NH2Cl treatment. After 3 h of NH2Cl treatment, when the apoptosis was beginning to increase, the cells showed cytochrome c release from mitochondria, proteolytic activation of caspase 9, and poly (ADP-ribose) polymerase cleavage, regardless of Fas stimulation. Z-VAD-fmk almost completely inhibited this poly (ADP-ribose) polymerase cleavage, but not cytochrome c release. By contrast, Fas stimulation alone resulted in neither cytochrome c release nor caspase 9 activation at 3 h, and the increase in the DEVD cleavage activity and apoptosis became evident at later time points. These results suggested that NH2Cl enhanced Fas-induced apoptosis through the cytochrome c release and caspase 9 activation at the early stage of apoptosis. Chloramines derived from acute inflammation may modify immune reactions, such as cell-mediated cytotoxicity and some autoimmune diseases, by the enhancement of Fas-induced apoptosis. (+info)
Vitamin C protects against and reverses specific hypochlorous acid- and chloramine-dependent modifications of low-density lipoprotein.
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Activated phagocytes produce the highly reactive oxidant hypochlorous acid (HOCl) via the myeloperoxidase-catalysed reaction of hydrogen peroxide with chloride ions. HOCl reacts readily with a number of susceptible targets on apolipoprotein B-100 of low-density lipoprotein (LDL), resulting in uncontrolled uptake of HOCl-modified LDL by macrophages. We have investigated the effects of vitamin C (ascorbate), an effective water-soluble antioxidant, on the HOCl- and chloramine-dependent modification of LDL. Co-incubation of vitamin C (25-200 microM) with LDL resulted in concentration-dependent protection against HOCl (25-200 microM)-mediated oxidation of tryptophan and lysine residues, formation of chloramines and increases in the relative electrophoretic mobility of LDL. Vitamin C also partially protected against oxidation of cysteine residues by HOCl, and fully protected against oxidation of these residues by the low-molecular-mass chloramines, N(alpha)-acetyl-lysine chloramine and taurine chloramine, and to a lesser extent monochloramine (each at 25-200 microM). Further, we found that HOCl (25-200 microM)-dependent formation of chloramines on apolipoprotein B-100 was fully reversed by 200 microM vitamin C; however, the loss of lysine residues and increase in relative electrophoretic mobility of LDL were only partially reversed, and the loss of tryptophan and cysteine residues was not reversed. Time-course experiments showed that the reversal by vitamin C of HOCl-dependent modifications became less efficient as the LDL was incubated for up to 4 h at 37 degrees C. These data show that vitamin C not only protects against, but also reverses, specific HOCl- and chloramine-dependent modifications of LDL. As HOCl-mediated LDL modifications have been strongly implicated in the pathogenesis of atherosclerosis, our data indicate that vitamin C could contribute to the anti-atherogenic defence against HOCl. (+info)
[(125)I]-GR231118: a high affinity radioligand to investigate neuropeptide Y Y(1) and Y(4) receptors.
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GR231118 (also known as 1229U91 and GW1229), a purported Y(1) antagonist and Y(4) agonist was radiolabelled using the chloramine T method. [(125)I]-GR231118 binding reached equilibrium within 10 min at room temperature and remained stable for at least 4 h. Saturation binding experiments showed that [(125)I]-GR231118 binds with very high affinity (K(d) of 0.09 - 0.24 nM) in transfected HEK293 cells with the rat Y(1) and Y(4) receptor cDNA and in rat brain membrane homogenates. No specific binding sites could be detected in HEK293 cells transfected with the rat Y(2) or Y(5) receptor cDNA demonstrating the absence of significant affinity of GR231118 for these two receptor classes. Competition binding experiments revealed that specific [(125)I]-GR231118 binding in rat brain homogenates is most similar to that observed in HEK293 cells transfected with the rat Y(1), but not rat Y(4), receptor cDNA. Autoradiographic studies demonstrated that [(125)I]-GR231118 binding sites were fully inhibited by the Y(1) antagonist BIBO3304 in most areas of the rat brain. Interestingly, high percentage of [(125)I]-GR231118/BIBO3304-insensitive binding sites were detected in few areas. These [(125)I]-GR231118/BIBO3304-insensitive binding sites likely represent labelling to the Y(4) receptor subtype. In summary, [(125)I]-GR231118 is a new radiolabelled probe to investigate the Y(1) and Y(4) receptors; its major advantage being its high affinity. Using highly selective Y(1) antagonists such as BIBO3304 or BIBP3226 it is possible to block the binding of [(125)I]-GR231118 to the Y(1) receptor allowing for the characterization and visualization of the purported Y(4) subtype. British Journal of Pharmacology (2000) 129, 37 - 46 (+info)