Development of novel mass spectrometric methods for identifying HOCl-induced modifications to proteins

Protein oxidation is thought to contribute to a number of inflammatory diseases, hence the development of sensitive and specific analytical techniques to detect oxidative PTMs (oxPTMs) in biological samples is highly desirable. Precursor ion scanning for fragment ions of oxidized amino acid residues was investigated as a label-free MS approach to mapping specific oxPTMs in a complex mixture of proteins. Using HOCl-oxidized lysozyme as a model system, it was found that the immonium ions of oxidized tyrosine and tryptophan formed in MS(2) analysis could not be used as diagnostic ions, owing to the occurrence of isobaric fragment ions from unmodified peptides. Using a double quadrupole linear ion trap mass spectrometer, precursor ion scanning was combined with detection of MS(3) fragment ions from the immonium ions and collisionally-activated decomposition peptide sequencing to achieve selectivity for the oxPTMs. For chlorotyrosine, the immonium ion at 170.1 m/z fragmented to yield diagnostic ions at 153.1, 134.1, and 125.1 m/z, and the hydroxytyrosine immonium ion at 152.1 m/z gave diagnostic ions at 135.1 and 107.1 m/z. Selective MS(3) fragment ions were also identified for 2-hydroxytryptophan and 5-hydroxytryptophan. The method was used successfully to map these oxPTMs in a mixture of nine proteins that had been treated with HOCl, thereby demonstrating its potential for application to complex biological samples.

Neutral super-oxidised solutions are effective in killing P. aeruginosa biofilms

Bacteria growing in biofilms can become up to 1000-fold more resistant to antibiotics and biocides as compared to their planktonic counterparts. As a result of this increased resistance, biofilms and biofilm-related infections cannot be effectively treated with conventional antibiotic therapy. The goal of this study was to determine the efficacy of three neutral pH, super-oxidised solutions (nSOSs, OIS-80, OIS-125, OIS-200, Microcyn Technology) varying in oxychlorine concentration (80, 125 and 200 ppm) against P. aeruginosa grown planktonically and as biofilms. Exposure for 20 s of exponential phase cells to any of the three solutions was sufficient to reduce viability by more than five logs. However, only exposure for 10 min to OIS-125 and OIS-200 for 10 min was sufficient to eradicate stationary phase P. aeruginosa cells. The efficacy of nSOSs on P. aeruginosa biofilms, grown to maturity in continuous flow tube reactors, was determined upon treatment up to 60 min. Viability pre- and post-treatment was determined by CFU counts. The effect of these solutions on P. aeruginosa biofilms and biofilm architecture was further visualised by confocal scanning laser microscopy and quantitatively analysed by COMSTAT. Under these experimental conditions, only OIS-125 and OIS-200 achieved a >3-log reduction and biofilm disaggregation within 30 min of exposure. Because OIS-125 and OIS-200 enhance the disaggregation of biofilms, their use in the treatment of surface-related biofilm infections deserves further investigation.

Inhibitory effect of hypochlorous acid on lower esophageal sphincter tone relaxation by vasoactive intestinal peptide

Under physiological conditions, hypochlorous acid (HOCl) is the major product of myeloperoxidase, a ferric heme enzyme released in inflammatory diseases. In the present study, we investigated the effect of HOCl compared to hydrogen peroxide (H2O2) on the vasoactive intestinal polypeptide (VIP)-induced relaxation of feline lower esophageal sphincter (LES) strips. Isometric tension on LES strips was measured using a force transducer. VIP induced the relaxation of basal LES tone in a concentration-dependent manner. Pretreatment with HOCl (10(-4) M) significantly reduced the VIP-induced relaxation at smaller concentrations than H2O2 (10(-3) M). VIP-induced relaxation is mediated via the Gi/o protein, since pretreatment with Pertussis Toxin (PTX) showed an inhibitory effect on the relaxation. HOCl showed an additional inhibitory effect on the reduced relaxation by PTX, indicating that HOCl might affect another G protein as well as Gi/o. However, HOCl did not affect SNP-, SIN-1-, and 8-br-cGMP-induced relaxation. Nor did HOCl modify the relaxation induced by either forskolin or db-cAMP in LES muscle strips. These results suggest that during short-term treatment, HOCl may damage the upstream events including G protein level, and result in alteration of LES tone in the feline esophagus, similar to the inhibitory effects of H2O2.

Hypochlorous acid oxidizes methionine and tryptophan residues in myoglobin

After acute myocardial infarction (AMI), infiltrating proinflammatory cells generate two-electron oxidants such as hypochlorous acid (HOCl). Myoglobin (Mb) is present at approximately 0.3 mM in cardiomyocytes and, therefore, represents a significant target for oxidation. Exposure of horse Mb (50 microM) to reagent HOCl (0-500 microM) or activated human neutrophils (4-40x10(6) cells/ml) yielded oxidized Mb (Mb(ox)) as judged by amino acid analysis and peptide mass mapping. HOCl/Mb ratios of 1-5 mol/mol gave Mb(ox) with up to four additional oxygen atoms. Hydrolysis of Mb(ox) followed by amino acid analysis indicated that methionine (Met) and tryptophan (Trp) residues were modified by HOCl. Peptide mass mapping revealed that Met55 was oxidized at a lower HOCl/Mb ratio than Met131 and this preceded Trp7/14 modification (susceptibility Met55>Met131>Trp7>Trp14). Incubation of Mb with activated neutrophils and physiological chloride anion yielded Mb(ox) with a composition similar to that determined with HOCl/Mb ratios <2 mol/mol, with oxidation of Met, but not Trp, detected. These data indicate that Mb undergoes site-specific oxidation depending on the HOCl/protein ratio. As Mb is released from necrotic cardiomyocytes into the vasculature after AMI, HOCl-modified Mb may be a useful surrogate marker to gauge the extent of myocardial inflammation.

Hypochlorous acid-induced modulation of cellular redox status in HeLa cells

Myeloperoxidase catalyzes the formation of hypochlorous acid (HOCI) via reaction of H2O2 with CI(-) ions. Although HOCI plays a major role in the human immune system by killing bacteria and other invading pathogens, excessive generation of this oxidant causes damage to tissues. Exposure of HeLa cells to HOCI decreased viability, inactivated antioxidant enzymes, damaged mitochondria, and modulated cellular redox status. HOCI also induced significant increases in cellular oxidative damage reflected by lipid peroxidation, protein oxidation, and DNA damage. HOCI-mediated oxidative damage to HeLa cells may perturb the cellular antioxidant defense mechanisms and subsequently lead to a pro-oxidant state.

Quantifying changes in the thiol redox proteome upon oxidative stress in vivo

Antimicrobial levels of reactive oxygen species (ROS) are produced by the mammalian host defense to kill invading bacteria and limit bacterial colonization. One main in vivo target of ROS is the thiol group of proteins. We have developed a quantitative thiol trapping technique termed OxICAT to identify physiologically important target proteins of hydrogen peroxide (H(2)O(2)) and hypochlorite (NaOCl) stress in vivo. OxICAT allows the precise quantification of oxidative thiol modifications in hundreds of different proteins in a single experiment. It also identifies the affected proteins and defines their redox-sensitive cysteine(s). Using this technique, we identified a group of Escherichia coli proteins with significantly (30-90%) oxidatively modified thiol groups, which appear to be specifically sensitive to either H(2)O(2) or NaOCl stress. These results indicate that individual oxidants target distinct proteins in vivo. Conditionally essential E. coli genes encode one-third of redox-sensitive proteins, a finding that might explain the bacteriostatic effect of oxidative stress treatment. We identified a select group of redox-regulated proteins, which protect E. coli against oxidative stress conditions. These experiments illustrate that OxICAT, which can be used in a variety of different cell types and organisms, is a powerful tool to identify, quantify, and monitor oxidative thiol modifications in vivo.

The combined performance of UV light and chlorine during reclaimed water disinfection

The combined effects of disinfectant agents on the microbiological quality of reclaimed water produced by two full-scale water reclamation plants in Catalonia, Spain, were examined in this work. All the disinfectant treatments tested led to the absence, or near absence, of E. coli in 100 mL samples of water, with log reductions of more than 3 log u. Hypochlorite reduced the bacterial concentrations. However, ultraviolet light was more effective than hypochlorite at reducing the concentrations of bacteriophages, viruses and pathogenic protozoa such as Cryptosporidium spp. We conclude that a combination of these two disinfectant agents is effective in protecting public health, as each agent acts to a different degree against the different groups of microorganisms studied. Further studies should investigate the combined action of disinfectant agents at water reclamation plants with ultraviolet light equipment in more favourable working conditions in order to assess their capacity to inactivate microorganisms.

Toxicogenomic response to chlorination includes induction of major virulence genes in Staphylococcus aureus

Despite the widespread use of chlorination for microbial control in aqueous environments, cellular response mechanisms of human pathogens, such as Staphylococcus aureus, against chlorination remain unknown. In this work, genome-wide transcriptional analysis was performed to elucidate cellular response of S. aureusto hypochlorous acid, an active antimicrobial product of chlorination in aqueous solution. Our results suggest that hypochlorous acid repressed transcription of genes involved in cell wall synthesis, membrane transport, protein synthesis, and primary metabolism, while amino acid synthesis genes were induced. Furthermore, hypochlorous acid induced transcription of genes encoding major virulence factors of S. aureus, such as exotoxins, hemolysins, leukocidins, coagulases, and surface adhesion proteins, which all play essential roles in staphylococcal virulence. This work implies that chlorination may stimulate production of virulence factors, which provides new insight into host-pathogen interactions and effects of chlorine application for microbial control.

Study of sugar beet cyst nematode life cycle using plant tissue culture method

After optimization of sterilizing of cyst and larva second stage of Heterodera schachtii, possibility of using nematode on seedlings of sugar beet (Beta vulgaris L.) in in vitro conditions were studied using sterilized larvae of beet cyst nematode. For this purpose, non sterile cysts were extracted from infected soil and hatched into zinc chloride solution with concentration of 0.5 g L(-1). Then, for preparation of sterile second stage larvae, several sterilizing treatments were used. Mean comparisons were performed between sterilized live larvae number by Duncan's method. Results showed that 70% ethanol for 1 min followed by 2.5% hypochlorite sodium for 5 minutes and 0.1% hypochlorite sodium for 20 min were best treatments for disinfecting cysts and larvae, respectively. In parallel, two nematode susceptible sugar beet varieties were applied to produce seedlings in in vitro culture. PG(oB) medium containing different hormonal compositions was used for producing of hairy roots and inoculation of seedling with sterilized larvae. After nematode inoculation tests, daily observations were done by counting cysts and stained roots and larvae under stereomicroscope. Between 5-12 cysts formed on the roots of each seedling from two varieties 40 days after inoculation. As a result, it seems that this technique can be used for sugar beet germplasm evaluation to screen nematode resistant genotypes in in vitro controlled condition.

Molecular monitoring of disinfection efficacy using propidium monoazide in combination with quantitative PCR

One of the major drawbacks of DNA-based microbial diagnostics is its inability to discriminate between live and dead bacteria. Due to the persistence of DNA in the environment after cells have lost their viability, DNA-based assays cannot assess pathogenic risk since signals can originate from both live and dead cells. Presented here is a potential application of the novel chemical propidium monoazide (PMA), which results in the selective suppression of DNA detection from dead cells. PMA can only penetrate dead cells with permeabilized cell membranes. Upon intercalation into the DNA, covalent crosslinkage of PMA to DNA is achieved through light exposure. This modification prevents the DNA from being amplified by PCR. The method, in combination with quantitative PCR as a diagnostic tool, successfully monitored the disinfection efficacy of hypochlorite, benzalkonium and heat on several model pathogens. Threshold cycle numbers increased with increasing disinfection strength after PMA treatment of samples compared to non-PMA treated samples. With some disinfectant-specific differences, monitoring viability loss with membrane integrity as an indicator seemed to be more conservative than monitoring viability loss with plate counts. Loss of viability after short UV-exposure could not be monitored with PMA as UV light affects viability by inducing DNA damage without directly affecting membrane permeability.

Ultraviolet spectrophotometric determination of nitrate: detecting nitrification rates and inhibition

Simple methods that rapidly detect nitrification inhibition are needed to enforce pretreatment programs and prevent upsets. The objective of this study was to demonstrate a rapid method for measuring nitrification inhibition by using nitrate generation rates (NGRs) coupled with direct UV detection of nitrate. The NGRs were measured with UV spectrophotometry at wavelengths between 225 and 240 nm, without chemical manipulation, and verified against ion chromatography. The method was shown to quickly and accurately measure nitrate concentrations after correcting for nitrite interference. Cadmium, hypochlorite and 1-chloro-2,4-dintrobenzene (CDNB) were tested for their ability to cause nitrification inhibition using this method. The CDNB was found to cause a correctable interference with the test, while hypochlorite provided an uncorrectable interference. Used as a batch method coupled with biotic and abiotic controls, this approach can be deployed at full-scale treatment plants as a relatively rapid (1.5 hours) means of identifying nitrification-inhibiting wastewaters.

Reactive oxidants regulate membrane repolarization and store-operated uptake of calcium by formyl peptide-activated human neutrophils

Although the rapid and considerable membrane depolarization response which accompanies activation of the phagocyte NADPH oxidase is due to transmembrane electron fluxes, little is known about the involvement of reactive oxidant species (ROS) in the subsequent repolarization response. In the current study, we have investigated the effects of superoxide dismutase (SOD), catalase, methionine, and the myeloperoxidase (MPO) inhibitors, sodium azide and 4-aminobenzoyl hydrazide (ABAH), as well as those of H(2)O(2) and HOCl (both at 100 microM) on the alterations in membrane potential which accompany activation of human neutrophils with the chemoattractant, FMLP (1 microM), and on store-operated uptake of Ca(2+). The generation of ROS by FMLP-activated neutrophils was monitored according to the magnitude of oxygen consumption and autoiodination, while spectrofluorimetric procedures were used to measure alterations in membrane potential and influx of Ca(2+). Treatment of the cells with H(2)O(2), and HOCl, significantly impeded membrane repolarization, while sodium azide, ABAH, methionine, and catalase exerted the opposite effects, potentiating both the rates and the magnitudes of membrane repolarization and store-operated uptake of Ca(2+). These observations demonstrate that NADPH oxidase regulates neutrophil membrane potential and Ca(2+) influx not only via its electrogenic activity, but also as a consequence of the generation of ROS.

Oxidative stress-induced apoptosis of bile duct cells in primary biliary cirrhosis

There has been a relative paucity of effort at defining effector mechanisms of biliary damage in PBC. We hypothesize that biliary cells are destroyed secondary to the immunologic relationships of inflammation and biliary epithelial apoptosis and, in particular, that biliary damage is a result of reduced levels of glutathione-S-transferase (GST), the production of hypochlorous acid (HOCl) and its association with eosinophil peroxidase (EPO). To address this issue, we examined the expression of EPO and GST in PBC and control livers and demonstrated an increase of EPO within the portal areas of PBC. We also demonstrated that macrophages have evidence of phagocytosed EPO. Furthermore, we studied the influence of HOCl on apoptosis in cultured human biliary epithelial cells (BEC) as well as the associated activity of Bcl-2, Bax, p-JNK, JNK, p53, Fas and caspase-3. HOC1-induced apoptosis in BEC in a dose-dependent fashion increased the activity of caspase-3 and the expression of p53 and p-JNK. Pretreatment with l-buthionine-(S,R)-sulfoximine, a glutathione (GSH) inhibitor, potentiated the sensitivity of BEC to HOCl-induced apoptosis. We conclude that intracellular GSH reduction leads directly to BEC apoptosis. Modulation of these events will be critical to reduce immune-mediated destruction.

Evaluation of liquid- and fog-based application of Sterilox hypochlorous acid solution for surface inactivation of human norovirus

Noroviruses (NVs) are the most frequent cause of outbreaks of gastroenteritis in common settings, with surface-mediated transfer via contact with fecally contaminated surfaces implicated in exposure. NVs are environmentally stable and persistent and have a low infectious dose. Several disinfectants have been evaluated for efficacy to control viruses on surfaces, but the toxicity and potential damage to treated materials limits their applicability. Sterilox hypochlorous acid (HOCl) solution (HAS) has shown broad-spectrum antimicrobial activity while being suitable for general use. The objectives of this study were to evaluate the efficacy of HAS to reduce NV both in aqueous suspensions and on inanimate carriers. HOCl was further tested as a fog to decontaminate large spaces. HOCl effectiveness was evaluated using nonculturable human NV measured by reverse transcriptase PCR (RT-PCR) and two surrogate viruses, coliphage MS2 and murine NV, that were detected by both infectivity and RT-PCR. Exposing virus-contaminated carriers of ceramic tile (porous) and stainless steel (nonporous) to 20 to 200 ppm of HOCl solution resulted in > or = 99.9% (> or = 3 log10) reductions of both infectivity and RNA titers of tested viruses within 10 min of exposure time. HOCl fogged in a confined space reduced the infectivity and RNA titers of NV, murine NV, and MS2 on these carriers by at least 99.9% (3 log10), regardless of carrier location and orientation. We conclude that HOCl solution as a liquid or fog is likely to be effective in disinfecting common settings to reduce NV exposures and thereby control virus spread via fomites.

Proteomic analysis of a hypochlorous acid-tolerant Listeria monocytogenes cultural variant exhibiting enhanced biofilm production

Following exposure of Listeria monocytogenes Scott A (SA) to hypochlorous acid, rough colony variants were identified that were tolerant of hypochlorous acid and produced increased amounts of biofilm. A derivative of one of these variants was smooth, produced even more biofilm, and exhibited greater biofilm chlorine resistance. The objective of this research was to compare the protein expression of a cultural variant to SA and to identify proteins that might be associated with biofilm production and chlorine tolerance. Suspension chlorine tolerance for several cultural variants (SAR, SAR5, and SBS) was determined by exposure to 60 to 120 ppm of hypochlorous acid for 5 min. Hypochlorous acid tolerance of biofilms was determined after growing biofilms on stainless steel and then exposing them to 200 ppm of hypochlorous acid for 5 min. All cultural variants were able to survive 120 ppm of hypochlorous acid in suspension. There was little difference in the hypochlorous acid tolerance of the cultural variant planktonic cells. The cultural variants produced greater amounts of biofilm than the common form of L. monocytogenes and were more tolerant of hypochlorous acid. The SBS variant was selected for proteomic comparison because it was the variant that produced the most biofilm and was the most tolerant of hypochlorous acid when grown as a biofilm. Protein expression of planktonic and biofilm cells of SBS was compared to SA by two-dimensional difference gel electrophoresis. The 50s ribosomal protein, L10, was down-regulated in biofilm SBS. Other proteins down-regulated in planktonic SBS were the peroxide resistance protein (Dpr) and a sugar-binding protein (LMO0181). This sugar-binding protein was also up-regulated in biofilm SBS. One protein spot down-regulated in planktonic SBS contained both 50s ribosomal protein L7/L12 and an unknown protein (LM01888).

Antioxidant properties of neohesperidin dihydrochalcone: inhibition of hypochlorous acid-induced DNA strand breakage, protein degradation, and cell death

Neohesperidin dihydrochalcone (NHDC), a non-nutritive sweetening agent, is simply produced by hydrogenation of neohesperidin. The aim of this study is to evaluate the antioxidant and radical scavenging properties of neohesperidin dihydrochalcone and other structurally related compounds (phloridzin, neohesperidin) toward different reactive radical and oxygen species including .ABTS+, .O2-, .OH, H2O2, and HOCl in vitro. NHDC showed remarkable radical scavenging activity against stable radical and reactive oxygen species (ROS) in concentration dependent manner. Especially, NHDC was the most potent inhibitor of H2O2 and HOCl. NHDC showed HOCl scavenging activity of 93.5% and H2O2 scavenging property of 73.5% which was more than those of all the tested compounds including ascorbic acid and BHT. Moreover, NHDC could inhibit protein degradation, plasmid DNA strand cleavage and HIT-T15, HUVEC cell death from HOCl attack while mannitol, BHT, and ascorbic acid could not protect them effectively. These results suggest that NHDC is a potent antioxidant, especially it is evaluated as a novel HOCl scavenger. This study implies the possibility of therapeutic effect of NHDC on ROS-related inflammatory diseases.

HDL oxidation compromises its influence on paraoxonase-1 secretion and its capacity to modulate enzyme activity

OBJECTIVE

The purpose of this study was to analyze the consequences of HDL oxidation for paraoxonase-1 metabolism and function.

METHODS AND RESULTS

HDL was oxidized with AAPH, copper ions, and hypochlorite. Secretion studies were performed using human paraoxonase-1-transfected cells lines and primary rat hepatocytes. Stability studies were performed with recombinant paraoxonase. Conditioned medium had significantly reduced paraoxonase-1 when Cu or AAPH-oxidized HDL was the acceptor complex (P<0.01); reduction was dose-dependent on the degree of oxidation. Oxidized HDL had a reduced capacity to stabilize/improve activity of secreted paraoxonase-1. Reduced secretion could not be attributed to enzyme inactivation by lipoperoxides, reduced binding affinity of HDL, or oxidation of the lipid component alone. Hypochlorite oxidation of HDL did not modify HDL-mediated paraoxonase-1 release, but activity of HDL-associated paraoxonase-1 was particularly sensitive to such treatment.

CONCLUSIONS

AAPH and copper, but not hypochlorite, oxidation of HDL compromises its ability to promote release of paraoxonase-1 and stabilize enzyme activity. HDL-associated paraoxonase-1 is highly sensitive to hypochlorite. Reducing paraoxonase-1 renders HDL susceptible to oxidation, which may compromise HDL function. It provides a novel example at the HDL level of the detrimental effects of oxidative stress, and underlines the need for further evaluation of the consequences of HDL oxidation.

Comparison of rinsing and sanitizing procedures for reducing bacterial pathogens on fresh cantaloupes and bell peppers

Increased consumption of fruits and vegetables is linked to health benefits but also to an increase in the number of outbreaks of foodborne illness. To determine the effectiveness of different sanitizing treatments for reducing bacterial pathogens on fresh produce, fresh cantaloupes and bell peppers were harvested and inoculated with suspensions of Salmonella Typhimurium and Escherichia coli O157:H7. The inoculated fruits were treated with water wash alone or were washed and then waxed or rinsed with 200 mg/liter hypochlorite, 10% Ca(OH)2, or 2% lactic acid solutions applied by dipping for 15 s or spraying for 15 s. Preliminary experiments with chlorine treatments indicated that spraying with a 200, 600, or 1,000 mg/liter hypochlorite solution reduced populations of both pathogens by 2.1 to 2.6 and 1.5 to 2.1 log CFU for Salmonella Typhimurium and E. coli O157:H7, respectively. In general, no differences were observed between chlorine solutions without pH adjustment (pH 9.2) and those with pH adjusted to 6.0. When different wash regimes were applied to inoculated cantaloupes or bell peppers, water wash alone produced significantly lower counts of both pathogens on bell peppers in comparison to untreated controls. However, this reduction was not observed on cantaloupes, indicating a possible surface effect. Application of 2% L-lactic acid by spray was the treatment that resulted in the lowest bacterial counts on both cantaloupes and bell peppers. This treatment did not produce any deleterious change in the sensorial characteristics of the products tested. None of the pathogens studied was able to grow during refrigerated storage (5 degrees C for cantaloupes and 10 degrees C for bell peppers), although numbers close to the detection limit of the counting method were found in randomly tested individual samples at days 14 and 28 of storage, indicating that these pathogens can survive for long periods on the produce surface. These results indicate that selected produce commodities could be sanitized at the packing facility. However, these interventions should not be applied as a replacement for but only as a complement to good hygiene practices.

Immunolocalization of hypochlorite-induced, catalase-bound free radical formation in mouse hepatocytes

The establishment of oxidants as mediators of signal transduction has renewed the interest of investigators in oxidant production and metabolism. In particular, H(2)O(2) has been demonstrated to play pivotal roles in mediating cell differentiation, proliferation, and death. Intracellular concentrations of H(2)O(2) are modulated by its rate of production and its rate of decomposition by catalase and peroxidases. In inflammation and infection, some of the H(2)O(2) is converted to hypochlorous acid, a key mediator of the host immune response against pathogens. In vivo HOCl production is mediated by myeloperoxidase, which uses excess H(2)O(2) to oxidize Cl(-). Mashino and Fridovich (Biochim. Biophys. Acta 956:63-69; 1988) observed that a high excess of HOCl over catalase inactivated the enzyme by mechanisms that remain unclear. The potential relevance of this as an alternative mechanism for catalase activity control and its potential impact on H(2)O(2)-mediated signaling and HOCl production compelled us to explore in depth the HOCl-mediated catalase inactivation pathways. Here, we demonstrate that HOCl induces formation of catalase protein radicals and carbonyls, which are temporally correlated with catalase aggregation. Hypochlorite-induced catalase aggregation and free radical formation that paralleled the enzyme loss of function in vitro were also detected in mouse hepatocytes treated with the oxidant. Interestingly, the novel immuno-spin-trapping technique was applied to image radical production in the cells. Indeed, in HOCl-treated hepatocytes, catalase and protein-DMPO nitrone adducts were colocalized in the cells' peroxisomes. In contrast, when hepatocytes from catalase-knockout mice were treated with hypochlorous acid, there was extensive production of free radicals in the plasma membrane. Because free radicals are short-lived species with fundamental roles in biology, the possibility of their detection and localization to cell compartments is expected to open new and stimulating research venues in the interface of chemistry, biology, and medicine.

Hypochlorite-modified albumin colocalizes with RAGE in the artery wall and promotes MCP-1 expression via the RAGE-Erk1/2 MAP-kinase pathway

Signal transduction via the endothelial receptor for advanced glycation end products (RAGE) plays a key role in vascular inflammation. Recent observations have shown that the myeloperoxidase-H2O2-chloride system of activated phagocytes is highly up-regulated under inflammatory conditions where hypochlorous acid (HOCl) is formed as the major oxidant. Albumin, an in vivo carrier for myeloperoxidase is highly vulnerable to oxidation and a major representative of circulating advanced oxidized proteins during inflammatory diseases. Immunohistochemical studies performed in the present study revealed marked colocalization of HOCl-modified epitopes with RAGE and albumin in sections of human atheroma, mainly at the endothelial lining. We show that albumin modified with physiologically relevant concentrations of HOCl, added as reagent or generated by the myeloperoxidase-H2O2-chloride system, is a high affinity ligand for RAGE. Albumin, modified by HOCl in the absence of free amino acids/carbohydrates/lipids to exclude formation of AGE-like structures, induced a rapid, RAGE-dependent activation of extracellular signal-regulated kinase 1/2 and up-regulation of the proinflammatory mediator monocyte chemoattractant protein-1. Cellular activation could be blocked either by a specific polyclonal anti-RAGE IgG and/or a specific mitogen-activated protein-kinase kinase inhibitor. The present study demonstrates that HOCl-modified albumin acts as a ligand for RAGE and promotes RAGE-mediated inflammatory complications.

Uncoupling of Endothelial Nitric Oxidase Synthase by Hypochlorous Acid

OBJECTIVE

The aim of the present study is to determine whether hypochlorous acid (HOCl), the major oxidant of leukocyte-derived myeloperoxidase (MPO), oxidizes the zinc-thiolate center of endothelial nitric oxide synthase (eNOS) and uncouples the enzyme.

METHODS AND RESULTS

Exposure of purified recombinant eNOS to HOCl (> or = 100 micromol/L) released zinc and disrupted the enzyme-active eNOS dimers. In parallel with increased detections of both O2*- and ONOO-, clinically relevant concentrations of HOCl disrupted eNOS dimers in cultured human umbilical vein endothelial cells (HUVEC) at concentration 10- to 100-fold lower than those required for recombinant eNOS. In HUVEC, HOCl increased the translocation of both p67(phox) and p47(phox) of NAD(P)H oxidase and the phosphorylation of atypical protein kinase C-zeta. Further, genetic or pharmacological inhibition of either NAD(P)H oxidase-derived O2*- or PKC-zeta or NOS abolished the effects of HOCl on eNOS dimers. Consistently, HOCl increased both O2*- and ONOO- and eNOS dimer oxidation in isolated mouse aortas from C57BL/6 but less in those of gp91(phox) knock-out mice. Finally, in human carotid atherosclerotic arteries, eNOS predominantly existed as monomers in parallel with increased staining of both MPO and 3-nitrotyrosine.

CONCLUSIONS

We conclude that HOCl uncouples eNOS by ONOO- generated from PKC-zeta-dependent NAD(P)H oxidase.

Novel model of inflammatory neointima formation reveals a potential role of myeloperoxidase in neointimal hyperplasia

Atherosclerosis, which is characterized by neointima formation, is an inflammatory disease. However, there is no inflammatory product-elicited neointimal model to support the causal role of inflammation in atherogenesis. We reported previously that leukocyte-derived MPO induces vascular injury responses such as endothelial dysfunction. We now test the role of MPO in inflammatory neointima formation. We infused temporarily isolated rat common carotid arteries with MPO (200 nM) and incubated for 1 h. We found that although MPO itself did not induce any neointima formation 2 wk after treatment, in the presence of its substrate, hydrogen peroxide, MPO was able to elicit neointimal hyperplasia. We further confirmed that MPO-induced neointimal hyperplasia is mediated by its product, hypochlorous acid (HOCl). HOCl elicited apoptosis both in intima and media followed by vascular proliferative response and resulted in neointima formation with a heterogeneous cell population. Both histological and functional features of HOCl-treated vessels are similar to those in atherosclerotic lesions. To our knowledge, this is the first direct in vivo demonstration of neointimal formation induced by a product of the inflammatory cascade. The results suggest that MPO may be a mediator for pathological neointima growth. This novel neointimal model could be useful for studying inflammation and atherosclerosis.

The pro-inflammatory oxidant hypochlorous acid induces Bax-dependent mitochondrial permeabilisation and cell death through AIF-/EndoG-dependent pathways

At sites of chronic inflammation, such as in the inflamed rheumatoid joint, activated neutrophils release hydrogen peroxide (H(2)O(2)) and the enzyme myeloperoxidase to catalyse the formation of hypochlorous acid (HOCl). 3-chlorotyrosine, a marker of HOCl in vivo, has been observed in synovial fluid proteins from rheumatoid arthritis patients. However the mechanisms of HOCl-induced cytotxicity are unknown. We determined the molecular mechanisms by which HOCl induced cell death in human mesenchymal progenitor cells (MPCs) differentiated into a chondrocytic phenotype as a model of human cartilage cells and show that HOCl induced rapid Bax conformational change, mitochondrial permeability and release of intra-mitochondrial pro-apoptotic proteins which resulted in nuclear translocation of AIF and EndoG. siRNA-mediated knockdown of Bax substantially prevented mitochondrial permeability, release of intra-mitochondrial pro-apoptotic proteins. Cell death was inhibited by siRNA-mediated knockdown of Bax, AIF or EndoG. Although we observed several biochemical markers of apoptosis, caspase activation was not detected either by western blotting, fluorescence activity assays or by using caspase inhibitors to inhibit cell death. This was further supported by findings that (1) in vitro exposure of recombinant human caspases to HOCl caused significant inhibition of caspase activity and (2) the addition of HOCl to staurosporine-treated MPCs inhibited the activity of cellular caspases. Our results show for the first time that HOCl induced Bax-dependent mitochondrial permeability which led to cell death without caspase activity by processes involving AIF/EndoG-dependent pathways. Our study provides a novel insight into the potential mechanisms of cell death in the inflamed human joint.

Hypochlorous acid enhances immunogenicity and uptake of allogeneic ovarian tumor cells by dendritic cells to cross-prime tumor-specific T cells

BACKGROUND

Ovarian cancer commonly relapses after remission and new strategies to target microscopic residual diseases are required. One approach is to activate tumor-specific cytotoxic T cells with dendritic cells loaded with tumor cells. In order to enhance their immunogenicity, ovarian tumor cells (SK-OV-3, which express two well-characterized antigens HER-2/neu and MUC-1) were killed by oxidation with hypochlorous acid (HOCl).

RESULTS

Treatment for 1 h with 60 microM HOCl was found to induce necrosis in all SK-OV-3 cells. Oxidized, but not live, SK-OV-3 was rapidly taken up by monocyte-derived dendritic cells, and induced partial dendritic cell maturation. Dendritic cells cultured from HLA-A2 healthy volunteers were loaded with oxidized SK-OV-3 (HLA-A2-) and co-cultured with autologous T cells. Responding T cells were tested for specificity after a further round of antigen stimulation. In ELISPOT assays, T cells produced interferon-gamma (IFN-gamma) in response to the immunizing cellular antigen, and also to peptides coding for MUC-1 and HER-2/neu HLA-A2 restricted epitopes, demonstrating efficient cross-presentation of cell-associated antigens. In contrast, no responses were seen after priming with heat-killed or HCl-killed SK-OV-3, indicating that HOCl oxidation and not cell death/necrosis per se enhanced the immunogenicity of SK-OV-3. Finally, T cells stimulated with oxidized SK-OV-3 showed no cross-reaction to oxidized melanoma cells, nor vice versa, demonstrating that the response was tumor-type specific.

CONCLUSIONS

Immunization with oxidized ovarian tumor cell lines may represent an improved therapeutic strategy to stimulate a polyclonal anti-tumor cellular immune response and hence extend remission in ovarian cancer.