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

The HOCl dry fog-is it safe for human cells?

This study aims to investigate if high-concentration HOCl fogging disinfection causes cytotoxicity and genotoxicity to cultured primary human skin fibroblasts. The cells were exposed to a dry fog of HOCl produced from solutions with a concentration of 300 ppm (5.72 mM) or 500 ppm (9.53 mM). After four times when fibroblasts were exposed to aerosolized HOCl at a concentration of 500 ppm for 9 minutes, significant cytotoxicity and genotoxicity effects were observed. Significant changes in the morphology of fibroblasts and cell death due to membrane disruption were observed, independent of the number of exposures. Flow cytometry analyses performed under these experimental conditions indicated a decrease in the number of cells with an intact cell membrane in the exposed samples compared to the sham samples, dropping to 49.1% of the total cells. Additionally, under the same conditions, the neutral comet assay results demonstrated significant DNA damage in the exposed cells. However, no analogous damages were found when the cells were exposed to aerosolized HOCl generated from a 300-ppm solution for 3 minutes, whether once or four times. Therefore, we have concluded that aerosolized HOCl in dry fog, with a concentration exceeding 300 ppm, can cause cytotoxic and genotoxic effects on human skin fibroblasts.

Antimicrobial efficacy, mode of action and in vivo use of hypochlorous acid (HOCl) for prevention or therapeutic support of infections

The objective is to provide a comprehensive overview of the rapidly developing field of the current state of research on in vivo use of hypochlorous acid (HOCl) to aid infection prevention and control, including naso-pharyngeal, alveolar, topical, and systemic HOCl applications. Also, examples are provided of dedicated applications in COVID-19. A brief background of HOCl's biological and chemical specifics and its physiological role in the innate immune system is provided to understand the effect of in vivo applications in the context of the body's own physiological defense mechanisms.

Myeloperoxidase and Advanced Oxidation Protein Products in the Cerebrospinal Fluid in Women and Men with Parkinson's Disease

Background: Myeloperoxidase (MPO) and advanced oxidation protein products, or AOPP (a type of MPO-derived chlorinated adducts), have been implicated in Parkinson´s disease (PD). Human MPO also show sex-based differences in PD. The objective was to study the relationship of MPO and AOPP in the cerebrospinal fluid (CSF) with motor features of idiopathic PD in male and female patients. Methods: MPO concentration and activity and AOPP content were measured in the CSF and serum in 34 patients and 30 controls. CSF leukocytes and the integrity of the blood-brain barrier were evaluated. Correlations of MPO and AOPP with clinical variables were examined. Results: The blood-brain barrier was intact and CSF leukocyte count was normal in all patients. CSF MPO concentration and activity were similar in the cohort of patients and controls, but CSF MPO content was significantly higher in male patients than in PD women (p = 0.0084). CSF MPO concentration correlated with disease duration in male and female patients (p < 0.01). CSF MPO concentration was significantly higher in men with disease duration ≥12 years versus the remainder of the male subjects (p < 0.01). Changes in CSF MPO in women were not significant. Serum MPO concentration and activity were significantly higher in all PD patients relative to controls (p < 0.0001). CSF MPO was not correlated with serum MPO. Serum AOPP were detected in all patients, but CSF AOPP was undetectable in 53% of patients. AOPP were not quantifiable in controls. Conclusions: CSF MPO is not a good biomarker for PD because mean CSF MPO concentration and activity are not different between the cohort of patients and controls. CSF MPO concentration positively correlated with disease duration in men and women, but CSF MPO is significantly enhanced only in male patients with disease duration longer than 12 years. It can be hypothesized that the MPO-related immune response in early-stage PD might be weak in all patients, but then the MPO-related immune response is progressively enhanced in men, not women. Since the blood-brain barrier is intact, and CSF MPO is not correlated with serum MPO, CSF myeloperoxidase would reflect MPO content in brain cells, not blood-derived cells. Finally, serum AOPP was detected in all patients, but not controls, which is consistent with the occurrence of chlorinative stress in blood serum in PD. The study of CSF AOPP as biomarker could not be assessed because the ELISA assay was hampered by its detection limit in the CSF.

Role of myeloperoxidase-derived oxidants in the induction of vascular smooth muscle cell damage

Myeloperoxidase (MPO) is released by activated immune cells and forms the oxidants hypochlorous acid (HOCl) and hypothiocyanous acid (HOSCN) from the competing substrates chloride and thiocyanate. MPO and the overproduction of HOCl are strongly linked with vascular cell dysfunction and inflammation in atherosclerosis. HOCl is highly reactive and causes marked cell dysfunction and death, whereas data with HOSCN are conflicting, and highly dependent on the nature of the cell type. In this study we have examined the reactivity of HOCl and HOSCN with human coronary artery smooth muscle cells (HCASMC), given the key role of this cell type in maintaining vascular function. HOCl reacts rapidly with the cells, resulting in extensive cell death by both necrosis and apoptosis, and increased levels of intracellular calcium. In contrast, HOSCN reacts more slowly, with cell death occurring only after prolonged incubation, and in the absence of the accumulation of intracellular calcium. Exposure of HCASMC to HOCl also influences mitochondrial respiration, decreases glycolysis, lactate release, the production of ATP, cellular thiols and glutathione levels. These changes occurred to varying extents on exposure of the cells to HOSCN, where evidence was also obtained for the reversible modification of cellular thiols. HOCl also induced alterations in the mRNA expression of multiple inflammatory and phenotypic genes. Interestingly, the extent and nature of these changes was highly dependent on the specific cell donor used, with more marked effects observed in cells isolated from diseased compared to healthy vessels. Overall, these data provide new insight into pathways promoting vascular dysfunction during chronic inflammation, support the use of thiocyanate as a means to modulate MPO-induced cellular damage in atherosclerosis.

Hypochlorous acid decreases antioxidant power, inhibits plasma membrane redox system and pathways of glucose metabolism in human red blood cells

Hypochlorous acid (HOCl) is generated at a high concentration by activated neutrophils at sites of inflammation in a myeloperoxidase catalyzed reaction. The increased and sustained production of HOCl at inflammatory sites may lead to tissue injury and this process is believed to play an important role in the progression of several diseases like chronic inflammation, atherosclerosis and some types of cancers. We have examined the effect of HOCl on human red blood cells (RBCs) under in vitro conditions. Treatment of RBC with different concentrations of HOCl (0.05-2.5 mM) at 37°C resulted in decreased activities of major antioxidant enzymes while the antioxidant power of RBC was weakened, as shown by lowered metal-reducing and free radical quenching ability of HOCl treated cells. RBC plasma membrane redox system was also inhibited suggesting membrane damage. The enzymes of glucose metabolism were inhibited indicating deranged energy metabolism. Electron microscopic images showed gross morphological changes in HOCl treated RBC. These results show that HOCl causes major alterations in the cellular antioxidant defense system and inhibition of glycolytic pathways, which increase the susceptibility of RBC to oxidative damage.

Neutrophil-Mediated Cardiac Damage After Acute Myocardial Infarction: Significance of Defining a New Target Cell Type for Developing Cardioprotective Drugs

Significance: Acute myocardial infarction (AMI) is a leading cause of death worldwide. Post-AMI survival rates have increased with the introduction of angioplasty as a primary coronary intervention. However, reperfusion after angioplasty represents a clinical paradox, restoring blood flow to the ischemic myocardium while simultaneously inducing ion and metabolic imbalances that stimulate immune cell recruitment and activation, mitochondrial dysfunction and damaging oxidant production. Recent Advances: Preclinical data indicate that these metabolic imbalances contribute to subsequent heart failure through sustaining local recruitment of inflammatory leukocytes and oxidative stress, cardiomyocyte death, and coronary microvascular disturbances, which enhance adverse cardiac remodeling. Both left ventricular dysfunction and heart failure are strongly linked to inflammation and immune cell recruitment to the damaged myocardium. Critical Issues: Overall, therapeutic anti-inflammatory and antioxidant agents identified in preclinical trials have failed in clinical trials. Future Directions: The versatile neutrophil-derived heme enzyme, myeloperoxidase (MPO), is gaining attention as an important oxidative mediator of reperfusion injury, vascular dysfunction, adverse ventricular remodeling, and atrial fibrillation. Accordingly, there is interest in therapeutically targeting neutrophils and MPO activity in the setting of heart failure. Herein, we discuss the role of post-AMI inflammation linked to myocardial damage and heart failure, describe previous trials targeting inflammation and oxidative stress post-AMI, highlight the potential adverse impact of neutrophil and MPO, and detail therapeutic options available to target MPO clinically in AMI patients.

Redox Signaling by Reactive Electrophiles and Oxidants

The concept of cell signaling in the context of nonenzyme-assisted protein modifications by reactive electrophilic and oxidative species, broadly known as redox signaling, is a uniquely complex topic that has been approached from numerous different and multidisciplinary angles. Our Review reflects on five aspects critical for understanding how nature harnesses these noncanonical post-translational modifications to coordinate distinct cellular activities: (1) specific players and their generation, (2) physicochemical properties, (3) mechanisms of action, (4) methods of interrogation, and (5) functional roles in health and disease. Emphasis is primarily placed on the latest progress in the field, but several aspects of classical work likely forgotten/lost are also recollected. For researchers with interests in getting into the field, our Review is anticipated to function as a primer. For the expert, we aim to stimulate thought and discussion about fundamentals of redox signaling mechanisms and nuances of specificity/selectivity and timing in this sophisticated yet fascinating arena at the crossroads of chemistry and biology.

Myeloperoxidase and Neurological Disorder: A Crosstalk

Myeloperoxidase (MPO) is a protein present in azurophilic granules, macrophages, and neutrophils that are released into extracellular fluid (ECF) during inflammation. MPO releases hypochlorous acid (HOCl) and other chlorinated species. It is derived from hydrogen peroxide (H₂O₂) showing response during inflammatory conditions and plays a role in the immune defense against pathogens. MPO may show unwanted effects by indirectly increasing the formation of reactive nitrogen species (RNS), reactive oxygen species (ROS), and tumor necrosis factor alpha (TNF-α) leading to inflammation and oxidative stress. As neuroinflammation is one of the inevitable biological components among most of neurological disorders, MPO and its receptor may be explored as candidates for future clinical interventions. The purpose of this review is to provide an overview of the pathophysiological characteristics of MPO and further explore the possibilities to target it for clinical use. Targeting MPO is promising and may open an avenue to act as a biomarker for diagnosis with defined risk stratification in patients with various neurological disorders.

Reactive Oxygen Species Donors Increase the Responsiveness of Dorsal Horn Neurons and Induce Mechanical Hyperalgesia in Rats

Our previous studies suggest that reactive oxygen species (ROS) scavengers have analgesic effect on neuropathic pain through spinal mechanisms in the rat. The studies suggest that superoxide in spinal cord is one of important mediators of persistent pain. To test the hypothesis that increase of superoxide-derived intermediates leads to central sensitization and pain, the effects of an intrathecal injection of chemical ROS donors releasing either OH^∙, OCl⁻, or H₂O₂ were examined on pain behaviors. Following treatment with t-BOOH (OH^∙ donor), dorsal horn neuron responses to mechanical stimuli in normal rats and the changes of neuronal excitability were explored on substantia gelatinosa (SG) neurons using whole-cell patch clamping recordings. Intrathecal administration of t-BOOH or NaOCl (OCl⁻ donor), but not H₂O₂, significantly decreased mechanical thresholds of hind paws. The responses of wide dynamic range neurons to mechanical stimuli increased after a local application of t-BOOH. The t-BOOH increased the frequency and the amplitude of excitatory postsynaptic potentials, depolarized membrane potential in SG neurons, and increased the frequency of action potentials evoked by depolarizing current pulses. These results suggest that elevated ROS, especially OH^∙, in the spinal cord sensitized dorsal horn neurons and produced hyperalgesia in normal rats.

Oxidised low density lipoprotein causes human macrophage cell death through oxidant generation and inhibition of key catabolic enzymes

Oxidised low density lipoprotein (oxLDL) is thought to be a significant contributor to the death of macrophage cells observed in advanced atherosclerotic plaques. Using human-derived U937 cells we have examined the effect of cytotoxic oxLDL on oxidative stress and cellular catabolism. Within 3h of the addition of oxLDL, there was a rapid, concentration dependent rise in cellular reactive oxygen species followed by the loss of cellular GSH, and the enzyme activity of both glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and aconitase. The loss of these catabolic enzymes was accompanied by the loss of cellular ATP and lower lactate generation. Addition of the macrophage antioxidant 7,8-dihydroneopterin inhibited the ROS generation, glutathione loss and catabolic inactivation. NOX was shown to be activated by oxLDL addition while apocynin inhibited the loss of GSH and cell viability. The data suggests that oxLDL triggers an excess of ROS production through NOX activation, and catabolic failure through thiol oxidation resulting in cell death.

Reaction of low-molecular-mass organoselenium compounds (and their sulphur analogues) with inflammation-associated oxidants

Selenium is an essential trace element in mammals, with the majority specifically encoded as seleno-L-cysteine into a range of selenoproteins. Many of these proteins play a key role in modulating oxidative stress, via either direct detoxification of biological oxidants, or repair of oxidised residues. Both selenium- and sulphur-containing residues react readily with the wide range of oxidants (including hydrogen peroxide, radicals, singlet oxygen and hypochlorous, hypobromous, hypothiocyanous and peroxynitrous acids) that are produced during inflammation and have been implicated in the development of a range of inflammatory diseases. Whilst selenium has similar properties to sulphur, it typically exhibits greater reactivity with most oxidants, and there are considerable differences in the subsequent reactivity and ease of repair of the oxidised species that are formed. This review discusses the chemistry of low-molecular-mass organoselenium compounds (e.g. selenoethers, diselenides and selenols) with inflammatory oxidants, with a particular focus on the reaction kinetics and product studies, with the differences in reactivity between selenium and sulphur analogues described in the selected examples. These data provide insight into the therapeutic potential of low-molecular-mass selenium-containing compounds to modulate the activity of both radical and molecular oxidants and provide protection against inflammation-induced damage. Progress in their therapeutic development (including modulation of potential selenium toxicity by strategic design) is demonstrated by a brief summary of some recent studies where novel organoselenium compounds have been used as wound healing or radioprotection agents and in the prevention of cardiovascular disease.

N-acetyl lysyltyrosylcysteine amide inhibits myeloperoxidase, a novel tripeptide inhibitor

Myeloperoxidase (MPO) plays important roles in disease by increasing oxidative and nitrosative stress and oxidizing lipoproteins. Here we report N-acetyl lysyltyrosylcysteine amide (KYC) is an effective inhibitor of MPO activity. We show KYC inhibits MPO-mediated hypochlorous acid (HOCl) formation and nitration/oxidation of LDL. Disulfide is the major product of MPO-mediated KYC oxidation. KYC (≤4,000 μM) does not induce cytotoxicity in bovine aortic endothelial cells (BAECs). KYC inhibits HOCl generation by phorbol myristate acetate (PMA)-stimulated neutrophils and human promyelocytic leukemia (HL-60) cells but not superoxide generation by PMA-stimulated HL-60 cells. KYC inhibits MPO-mediated HOCl formation in BAEC culture and protects BAECs from MPO-induced injury. KYC inhibits MPO-mediated lipid peroxidation of LDL whereas tyrosine (Tyr) and tryptophan (Trp) enhance oxidation. KYC is unique as its isomers do not inhibit MPO activity, or are much less effective. Ultraviolet-visible spectral studies indicate KYC binds to the active site of MPO and reacts with compounds I and II. Docking studies show the Tyr of KYC rests just above the heme of MPO. Interestingly, KYC increases MPO-dependent H₂O₂ consumption. These data indicate KYC is a novel and specific inhibitor of MPO activity that is nontoxic to endothelial cell cultures. Accordingly, KYC may be useful for treating MPO-mediated vascular disease.

New insight into amphotericin B resistance in Aspergillus terreus

Amphotericin B (AMB) is the predominant antifungal drug, but the mechanism of resistance is not well understood. We compared the in vivo virulence of an AMB-resistant Aspergillus terreus (ATR) isolate with that of an AMB-susceptible A. terreus isolate (ATS) using a murine model for disseminated aspergillosis. Furthermore, we analyzed the molecular basis of intrinsic AMB resistance in vitro by comparing the ergosterol content, cell-associated AMB levels, AMB-induced intracellular efflux, and prooxidant effects between ATR and ATS. Infection of immunosuppressed mice with ATS or ATR showed that the ATS strain was more lethal than the ATR strain. However, AMB treatment improved the outcome in ATS-infected mice while having no positive effect on the animals infected with ATR. The in vitro data demonstrated that ergosterol content is not the molecular basis for AMB resistance. ATR absorbed less AMB, discharged more intracellular compounds, and had better protection against oxidative damage than the susceptible strain. Our experiments showed that ergosterol content plays a minor role in intrinsic AMB resistance and is not directly associated with intracellular cell-associated AMB content. AMB might exert its antifungal activity by oxidative injury rather than by an increase in membrane permeation.

Intracellular glutathione protects human monocyte-derived macrophages from hypochlorite damage

AIMS

Macrophages must function in an inflammatory environment of high oxidative stress due to the production of various oxidants. Hypochlorous acid (HOCl) is a potent cytotoxic agent generated by neutrophils and macrophages within inflammatory sites. This study determines whether glutathione is the key factors governing macrophage resistance to HOCl.

MAIN METHODS

Human monocyte derived macrophages (HMDM) were differentiated from human monocytes prepared from human blood. The HMDM cells were exposed to micromolar concentrations of HOCl and the timing of the cell viability loss was measured. Cellular oxidative damage was measured by loss of glutathione, cellular ATP, tyrosine oxidation, and inactivation of glyceraldehyde 3-phosphate dehydrogenase (GAPDH).

KEY FINDINGS

HOCl causes a rapid loss in HMDM cell viability above threshold concentrations. The cell death occurred within 10 min of treatment with the morphological characteristics of necrosis. The HOCl caused the extensive cellular protein oxidation with the loss of tyrosine residue and inactivation of GAPDH, which was accompanied with the loss of cellular ATP. This cellular damage was only observed after the loss of intracellular GSH from the cell. Removal of intracellular GSH with diethyl maleate (DEM) increased the cells' sensitivity to HOCl damage while protecting the intracellular GSH pool with the antioxidant 7,8-dihydroneopterin prevented the HOCl mediated viability loss. Variations in the HOCl LD(50) for inducing cell death were strongly correlated with initial intracellular GSH levels.

SIGNIFICANCE

In HMDM cells scavenging of HOCl by intracellular glutathione is sufficient to protect against oxidative loss of key metabolic functions within the cells.

HOCl causes necrotic cell death in human monocyte derived macrophages through calcium dependent calpain activation

The abundance of dead macrophages in close proximity to HOCl-modified proteins in advanced atherosclerotic plaques implicates HOCl in the killing of macrophages and the formation of the necrotic core region. The mechanism of HOCl mediated death of macrophages was unknown, so using human monocyte derived macrophages (HMDM) we here have shown that HOCl causes a rapid necrotic cell death characterized by loss of MTT reduction, cellular ATP and cell lysis without caspase-3 activation in HMDM cells. The HOCl causes a rise in cytosolic calcium level via the plasma membrane L- and T-type calcium channels and endoplasmic reticulum RyR channel. Blocking of the calcium channels or the addition of calpain inhibitors prevents the HOCl mediated loss of mitochondrial potential, lysosome failure and HMDM cell death. Blocking MPT-pore formation with cyclosporin A also prevents the loss of mitochondrial membrane potential, lysosomal destabilization and HMDM cell death. Blocking the calcium mitochondrial uniporter with ruthenium red also blocks the loss of mitochondrial potential but only at high concentrations. HOCl appears to cause HMDM cell death through destabilization of cytosolic calcium control resulting in the failure of both the mitochondria and lysosomes.

S-bacillithiolation protects against hypochlorite stress in Bacillus subtilis as revealed by transcriptomics and redox proteomics

Protein S-thiolation is a post-translational thiol-modification that controls redox-sensing transcription factors and protects active site cysteine residues against irreversible oxidation. In Bacillus subtilis the MarR-type repressor OhrR was shown to sense organic hydroperoxides via formation of mixed disulfides with the redox buffer bacillithiol (Cys-GlcN-Malate, BSH), termed as S-bacillithiolation. Here we have studied changes in the transcriptome and redox proteome caused by the strong oxidant hypochloric acid in B. subtilis. The expression profile of NaOCl stress is indicative of disulfide stress as shown by the induction of the thiol- and oxidative stress-specific Spx, CtsR, and PerR regulons. Thiol redox proteomics identified only few cytoplasmic proteins with reversible thiol-oxidations in response to NaOCl stress that include GapA and MetE. Shotgun-liquid chromatography-tandem MS analyses revealed that GapA, Spx, and PerR are oxidized to intramolecular disulfides by NaOCl stress. Furthermore, we identified six S-bacillithiolated proteins in NaOCl-treated cells, including the OhrR repressor, two methionine synthases MetE and YxjG, the inorganic pyrophosphatase PpaC, the 3-D-phosphoglycerate dehydrogenase SerA, and the putative bacilliredoxin YphP. S-bacillithiolation of the OhrR repressor leads to up-regulation of the OhrA peroxiredoxin that confers together with BSH specific protection against NaOCl. S-bacillithiolation of MetE, YxjG, PpaC and SerA causes hypochlorite-induced methionine starvation as supported by the induction of the S-box regulon. The mechanism of S-glutathionylation of MetE has been described in Escherichia coli also leading to enzyme inactivation and methionine auxotrophy. In summary, our studies discover an important role of the bacillithiol redox buffer in protection against hypochloric acid by S-bacillithiolation of the redox-sensing regulator OhrR and of four enzymes of the methionine biosynthesis pathway.

Myeloperoxidase-derived oxidation: mechanisms of biological damage and its prevention

There is considerable interest in the role that mammalian heme peroxidase enzymes, primarily myeloperoxidase, eosinophil peroxidase and lactoperoxidase, may play in a wide range of human pathologies. This has been sparked by rapid developments in our understanding of the basic biochemistry of these enzymes, a greater understanding of the basic chemistry and biochemistry of the oxidants formed by these species, the development of biomarkers that can be used damage induced by these oxidants in vivo, and the recent identification of a number of compounds that show promise as inhibitors of these enzymes. Such compounds offer the possibility of modulating damage in a number of human pathologies. This reviews recent developments in our understanding of the biochemistry of myeloperoxidase, the oxidants that this enzyme generates, and the use of inhibitors to inhibit such damage.

Inhibition of lung fluid clearance and epithelial Na+ channels by chlorine, hypochlorous acid, and chloramines

We investigated the mechanisms by which chlorine (Cl(2)) and its reactive byproducts inhibit Na(+)-dependent alveolar fluid clearance (AFC) in vivo and the activity of amiloride-sensitive epithelial Na(+) channels (ENaC) by measuring AFC in mice exposed to Cl(2) (0-500 ppm for 30 min) and Na(+) and amiloride-sensitive currents (I(Na) and I(amil), respectively) across Xenopus oocytes expressing human alpha-, beta-, and gamma-ENaC incubated with HOCl (1-2000 microm). Both Cl(2) and HOCl-derived products decreased AFC in mice and whole cell and single channel I(Na) in a dose-dependent manner; these effects were counteracted by serine proteases. Mass spectrometry analysis of the oocyte recording medium identified organic chloramines formed by the interaction of HOCl with HEPES (used as an extracellular buffer). In addition, chloramines formed by the interaction of HOCl with taurine or glycine decreased I(Na) in a similar fashion. Preincubation of oocytes with serine proteases prevented the decrease of I(Na) by HOCl, whereas perfusion of oocytes with a synthetic 51-mer peptide corresponding to the putative furin and plasmin cleaving segment in the gamma-ENaC subunit restored the ability of HOCl to inhibit I(Na). Finally, I(Na) of oocytes expressing wild type alpha- and gamma-ENaC and a mutant form of beta ENaC (S520K), known to result in ENaC channels locked in the open position, were not altered by HOCl. We concluded that HOCl and its reactive intermediates (such as organic chloramines) inhibit ENaC by affecting channel gating, which could be relieved by proteases cleavage.

Hypochlorous acid-induced heme oxygenase-1 gene expression promotes human endothelial cell survival

Hypochlorous acid (HOCl) is a unique oxidant generated by the enzyme myeloperoxidase that contributes to endothelial cell dysfunction and death in atherosclerosis. Since myeloperoxidase localizes with heme oxygenase-1 (HO-1) in and around endothelial cells of atherosclerotic lesions, the present study investigated whether there was an interaction between these two enzymes in vascular endothelium. Treatment of human endothelial cells with the myeloperoxidase product HOCl stimulated a concentration- and time-dependent increase in HO-1 protein that resulted in a significant rise in carbon monoxide (CO) production. The induction of HO-1 protein was preceded by a prominent increase in HO-1 mRNA and total and nuclear factor-erythroid 2-related factor 2 (Nrf2). In addition, HOCl induced a significant rise in HO-1 promoter activity that was blocked by mutating the antioxidant response element (ARE) in the promoter or by overexpressing a dominant-negative mutant of Nrf2. The HOCl-mediated induction of Nrf2 or HO-1 was blocked by the glutathione donor N-acetyl-l-cysteine but was unaffected by ascorbic or uric acid. Finally, treatment of endothelial cells with HOCl stimulated mitochondrial dysfunction, caspase-3 activation, and cell death that was potentiated by the HO inhibitor, tin protoporphyrin-IX, or by the knockdown of HO-1, and reversed by the exogenous administration of biliverdin, bilirubin, or CO. These results demonstrate that HOCl induces HO-1 gene transcription via the activation of the Nrf2/ARE pathway to counteract HOCl-mediated mitochondrial dysfunction and cell death. The ability of HOCl to activate HO-1 gene expression may represent a critical adaptive response to maintain endothelial cell viability at sites of vascular inflammation and atherosclerosis.

Hormesis and adaptive cellular control systems

Hormetic dose response occurs for many endpoints associated with exposures of biological organisms to environmental stressors. Cell-based U- or inverted U-shaped responses may derive from common processes involved in activation of adaptive responses required to protect cells from stressful environments. These adaptive pathways extend the region of cellular homeostasis and are protective against ultimate cell, organ, and system toxicity. However, the activation of stress responses carries a significant energetic cost to the cell, leading to alterations of a variety of basal cellular functions in adapted or stressed cells. This tradeoff of resources between the unstressed and adapted states may lead to U-or inverted U-shaped dose response curves for some precursor endpoints. We examine this general hypothesis with chlorine, a prototype oxidative stressor, using a combination of cellular studies with gene expression analysis of response pathways and with computational modeling of activation of control networks. Discrete cellular states are expected as a function of exposure concentration and duration. These cellular states include normal functioning state, adaptive and stressed states at mild to intermediate exposures, and overt toxicity in the presence of an overwhelming concentration of stressors. These transitions can be used to refine default risk assessment practices that do not currently accommodate adaptive responses.

Glutathione protects Lactococcus lactis against acid stress

Previously we showed that glutathione (GSH) can protect Lactococcus lactis against oxidative stress (Y. Li et al., Appl. Environ. Microbiol. 69:5739-5745, 2003). In the present study, we show that the GSH imported by L. lactis subsp. cremoris SK11 or produced by engineered L. lactis subsp. cremoris NZ9000 can protect both strains against a long-term mild acid challenge (pH 4.0) and a short-term severe acid challenge (pH 2.5). This shows for the first time that GSH can protect a gram-positive bacterium against acid stress. During acid challenge, strain SK11 containing imported GSH and strain NZ9000 containing self-produced GSH exhibited significantly higher intracellular pHs than the control. Furthermore, strain SK11 containing imported GSH had a significantly higher activity of glyceraldehyde-3-phosphate dehydrogenase than the control. These results suggest that the acid stress resistance of starter culture can be improved by selecting L. lactis strains capable of producing or importing GSH.

Activated neutrophils inhibit nucleotide excision repair in human pulmonary epithelial cells: role of myeloperoxidase

Neutrophils are thought to affect pulmonary carcinogenesis by promoting the metabolism of inhaled chemical carcinogens, causing enhanced formation of promutagenic DNA adducts. We hypothesized that neutrophils interfere with the removal of such DNA adducts by inhibiting nucleotide excision repair (NER) in target cells. Human alveolar epithelial cells (A549) were cocultured with activated neutrophils, and we observed a significant reduction of NER in the A549 cells, which was abrogated by addition of the myeloperoxidase (MPO) inhibitor 4-aminobenzoic acid hydrazide. The inhibitory effect of neutrophils could be mimicked by the MPO product hypochlorous acid (HOCl), which caused an acute, dose-dependent inhibition of NER in A549 cells. This was independent of cytotoxicity or ATP loss and persisted up to 24 h. These data were supported by showing that HOCl caused a delayed removal of DNA adducts in benzo[a]pyrene-diolepoxide-exposed A549 cells. The acute HOCl-induced inhibition of NER can only partly be explained by oxidative modification of repair proteins. To explain the more persistent effects of HOCl, we analyzed the expression of NER genes and found that HOCl significantly reduced XPC expression. In conclusion, these data indicate that neutrophils are potent inhibitors of nucleotide excision repair. This may provide a further biological explanation for the association between inflammation and lung cancer development.

Effects of biological oxidants on the catalytic activity and structure of group VIA phospholipase A2

Group VIA phospholipase A(2) (iPLA(2)beta) is expressed in phagocytes, vascular cells, pancreatic islet beta-cells, neurons, and other cells and plays roles in transcriptional regulation, cell proliferation, apoptosis, secretion, and other events. A bromoenol lactone (BEL) suicide substrate used to study iPLA(2)beta functions inactivates iPLA(2)beta by alkylating Cys thiols. Because thiol redox reactions are important in signaling and some cells that express iPLA(2)beta produce biological oxidants, iPLA(2)beta might be subject to redox regulation. We report that biological concentrations of H(2)O(2), NO, and HOCl inactivate iPLA(2)beta, and this can be partially reversed by dithiothreitol (DTT). Oxidant-treated iPLA(2)beta modifications were studied by LC-MS/MS analyses of tryptic digests and included DTT-reversible events, e.g., formation of disulfide bonds and sulfenic acids, and others not so reversed, e.g., formation of sulfonic acids, Trp oxides, and Met sulfoxides. W(460) oxidation could cause irreversible inactivation because it is near the lipase consensus sequence ((463)GTSTG(467)), and site-directed mutagenesis of W(460) yields active mutant enzymes that exhibit no DTT-irreversible oxidative inactivation. Cys651-sulfenic acid formation could be one DTT-reversible inactivation event because Cys651 modification correlates closely with activity loss and its mutagenesis reduces sensitivity to inhibition. Intermolecular disulfide bond formation might also cause reversible inactivation because oxidant-treated iPLA(2)beta contains DTT-reducible oligomers, and oligomerization occurs with time- and temperature-dependent iPLA(2)beta inactivation that is attenuated by DTT or ATP. Subjecting insulinoma cells to oxidative stress induces iPLA(2)beta oligomerization, loss of activity, and subcellular redistribution and reduces the rate of release of arachidonate from phospholipids. These findings raise the possibility that redox reactions affect iPLA(2)beta functions.

IkappaB is a sensitive target for oxidation by cell-permeable chloramines: inhibition of NF-kappaB activity by glycine chloramine through methionine oxidation

Hypochlorous acid (HOCl) is produced by the neutrophil enzyme, myeloperoxidase, and reacts with amines to generate chloramines. These oxidants react readily with thiols and methionine and can affect cell-regulatory pathways. In the present study, we have investigated the ability of HOCl, glycine chloramine (Gly-Cl) and taurine chloramine (Tau-Cl) to oxidize IkappaBalpha, the inhibitor of NF-kappaB (nuclear factor kappaB), and to prevent activation of the NF-kappaB pathway in Jurkat cells. Glycine chloramine (Gly-Cl) and HOCl were permeable to the cells as determined by oxidation of intracellular GSH and inactivation of glyceraldehyde-3-phosphate dehydrogenase, whereas Tau-Cl showed no detectable cell permeability. Both Gly-Cl (20-200 muM) and HOCl (50 microM) caused oxidation of IkappaBalpha methionine, measured by a shift in electrophoretic mobility, when added to the cells in Hanks buffer. In contrast, a high concentration of Tau-Cl (1 mM) in Hanks buffer had no effect. However, Tau-Cl in full medium did modify IkappaBalpha. This we attribute to chlorine exchange with other amines in the medium to form more permeable chloramines. Oxidation by Gly-Cl prevented IkappaBalpha degradation in cells treated with TNFalpha (tumour necrosis factor alpha) and inhibited nuclear translocation of NF-kappaB. IkappaBalpha modification was reversed by methionine sulphoxide reductase, with both A and B forms required for complete reduction. Oxidized IkappaBalpha persisted intracellularly for up to 6 h. Reversion occurred in the presence of cycloheximide, but was prevented if thioredoxin reductase was inhibited, suggesting that it was due to endogenous methionine sulphoxide reductase activity. These results show that cell-permeable chloramines, either directly or when formed in medium, could regulate NF-kappaB activation via reversible IkappaBalpha oxidation.

Reaction of protein chloramines with DNA and nucleosides: evidence for the formation of radicals, protein-DNA cross-links and DNA fragmentation

Stimulated phagocyte cells produce the oxidant HOCl, via the release of the enzyme myeloperoxidase and hydrogen peroxide. HOCl is important in bacterial cell killing, but excessive or misplaced generation can damage the host tissue and may lead to the development of certain diseases such as cancer. The role of HOCl in the oxidation of isolated proteins, DNA and their components has been investigated extensively, but little work has been performed on the protein-DNA (nucleosome) complexes present in eukaryotic cell nuclei. Neither the selectivity of damage in such complexes nor the possibility of transfer of damage from the protein to DNA or vice versa, has been studied. In the present study, kinetic modelling has been employed to predict that reaction occurs predominantly with the protein and not with the DNA in the nucleosome, using molar HOCl excesses of up to 200-fold. With 50-200-fold excesses, 50-80% of the HOCl is predicted to react with histone lysine and histidine residues to yield chloramines. The yield and stability of such chloramines predicted by these modelling studies agrees well with experimental data. Decomposition of these species gives protein-derived, nitrogen-centred radicals, probably on the lysine side chains, as characterized by the EPR and spin-trapping experiments. It is shown that isolated lysine, histidine, peptide and protein chloramines can react with plasmid DNA to cause strand breaks. The protection against such damage afforded by the radical scavengers Trolox (a water-soluble alpha-tocopherol derivative) and 5,5-dimethyl-1-pyrroline-N-oxide suggests a radical-mediated process. The EPR experiments and product analyses have also provided evidence for the rapid addition of protein radicals, formed on chloramine decomposition, to pyrimidine nucleosides to give nucleobase radicals. Further evidence for the formation of such covalent cross-links has been obtained from experiments performed using (3)H-lysine and (14)C-histidine chloramines. These results are consistent with the predictions of the kinetic model and suggest that histones are major targets for HOCl in the nucleosome. Furthermore, the resulting protein chloramines and the radicals derived from them may act as contributing agents in HOCl-mediated DNA oxidation.