Oxidation of thiols and modification of redox-sensitive signaling in human lung epithelial cells exposed to Pseudomonas pyocyanin

Homogeneously catalytic oxidation of phenanthrene by the reaction of extracellular secretions of pyocyanin and Nicotinamide Adenine Dinucleotide

Application of biological methods on polycyclic aromatic hydrocarbons (PAHs) treatment is always limited by its low degradation efficiency. In this work, a catalytic oxidation pathway of phenanthrene resulted by extracellular secretions of P. aeruginosa NY3 was proposed. Results of the in vitro experiments showed that, the extracellular secretions of Pyocyanin (Pyo) and Nicotinamide Adenine Dinucleotide (NADH) acted as homogeneous catalysts because which produced H₂O₂, hydroxyl free radical and superoxide anion radical continuously under aerobic conditions. These produced reactive oxygen species oxidized the phenanthrene in aqueous solution, leading to the cleavage of the phenanthrene ring and the formation of phthalates products and low molecular weight metabolites (such as alkanoic acids). The ratio of BOD₅/COD of phenanthrene-containing wastewaters was greatly improved after treating with Pyo and NADH. Results of the in vivo experiments showed that, pre-degradation of phenanthrene by extracellular fluid simultaneously containing Pyo and NADH, promoted cell growth of P. aeruginosa NY3, which confirmed the improvement of bioavalability of phenanthrene-containing wastewaters by the catalytic oxidation of Pyo and NADH. Further details of the free radical detection indicated that, the increase in secretion of Pyo by a bacterium was favorable to the production of H₂O₂ in the extracellular fluid.

N-acetylcysteine prevents glutathione decrease and does not interfere with paracetamol antinociceptive effect at therapeutic dosage: a randomized double-blind controlled trial in healthy subjects

Paracetamol (APAP) may lead to hepatic changes even at therapeutic dosages. Glutathione (GSH) plays a pivotal role in APAP metabolism as it allows the detoxification of a toxic metabolite. N-Acetylcysteine (NAC) is APAP antidote, is also largely used as a mucoactive drug and is often associated with APAP. This study aims at evaluating if 1- NAC modifies APAP pain efficacy and 2- NAC prevents glutathione depletion with APAP at therapeutic doses. This double-blind randomized controlled study (NCT02206178) was carried out in 24 healthy volunteers. APAP was given for 4 days (1 g ×4 daily) with NAC or with placebo. Thermal pain tests, whole blood GSH, and hepatic enzymes (ASAT, ALAT) were measured before (D0) and after (D4) oral APAP-NAC or APAP-placebo intake. anova for repeated measures adapted to cross-overdesign was performed and a two-tailed type I error was fixed at 5%. The primary endpoint was the area under the curve (0-240 min) of pain intensity (Numerical Scale) after thermal pain stimulation using Pathway-Medoc^® . APAP antinociceptive effect was similar in both groups. GSH was maintained to its baseline value in the APAP/NAC group but diminished in the APAP/placebo group (P = 0.033). This study shows for the first time that APAP antinociceptive effectiveness is not influenced by NAC. It also shows that the effect of APAP at therapeutic dosage on GSH may be counteracted by NAC. These issues are particularly important for patients as APAP is often prescribed for years as a first-line pain treatment and further trials in patients are now warranted.

Evidences of extracellular abiotic degradation of hexadecane through free radical mechanism induced by the secreted phenazine compounds of P. aeruginosa NY3

The aim of this work was to investigate the effects of secreted extracellular phenazine compounds (PHCs) on the degradation efficiency of alkanes by P. aeruginosa NY3. Under aerobic conditions, the PHCs secreted by P. aeruginosa NY3 initiate the oxidation of alkanes outside cells, in coupling with some reducing agents, such as β-Nicotinamide adenine dinucleotide, reduced disodium salt (NADH) or reduced glutathione (GSH). This reaction might be via free radical reactions similar to Fenton Oxidation Reaction (FOR). P. aeruginosa NY3 secretes pyocyanin (Pyo), 1-hydroxyphenazine (HPE), phenazine-1-carboxylic acid (PCA), and phenazine-1-amide (PCN) simultaneously. The cell-free extracellular fluid containing these four PHCs degrades hexadecane effectively. The observation of Electron Spin Resonance (EPR) signals of superoxide anion radical (O₂^-), hydroxyl radical (OH) and/or carbon free radicals (R) both in vivo and in vitro suggested the degradation of hexadecane could be via a free radical pathway. Secretion of PHCs has been found to be characteristic of Pseudomonas which is often involved in or related to the degradation of organic pollutants. Our work suggested that certain organic contaminants may be oxidized through ubiquitously extracellular abiotic degradation by the free radicals produced during bio-remediation and bio-treatment.

The bacterial pigment pyocyanin inhibits the NLRP3 inflammasome through intracellular reactive oxygen and nitrogen species

Inflammasomes are cytosolic complexes that mature and secrete the inflammatory cytokines interleukin 1β (IL-1β) and IL-18 and induce pyroptosis. The NLRP3 (NACHT, LRR, and PYD domains–containing protein 3) inflammasome detects many pathogen- and danger-associated molecular patterns, and reactive oxygen species (ROS)/reactive nitrogen species (RNS) have been implicated in its activation. The phenazine pyocyanin (PCN) is a virulence factor of Pseudomonas aeruginosa and generates superoxide in cells. Here we report that PCN inhibits IL-1β and IL-18 release and pyroptosis upon NLRP3 inflammasome activation in macrophages by preventing speck formation and Caspase-1 maturation. Of note, PCN did not regulate the AIM2 (absent in melanoma 2) or NLRC4 inflammasomes or tumor necrosis factor (TNF) secretion. Imaging of the fluorescent glutathione redox potential sensor Grx1-roGFP2 indicated that PCN provokes cytosolic and nuclear but not mitochondrial redox changes. PCN-induced intracellular ROS/RNS inhibited the NLRP3 inflammasome posttranslationally, and hydrogen peroxide or peroxynitrite alone were sufficient to block its activation. We propose that cytosolic ROS/RNS inhibit the NLRP3 inflammasome and that PCN's anti-inflammatory activity may help P. aeruginosa evade immune recognition.

Human oxygen sensing may have origins in prokaryotic elongation factor Tu prolyl-hydroxylation

The roles of 2-oxoglutarate (2OG)-dependent prolyl-hydroxylases in eukaryotes include collagen stabilization, hypoxia sensing, and translational regulation. The hypoxia-inducible factor (HIF) sensing system is conserved in animals, but not in other organisms. However, bioinformatics imply that 2OG-dependent prolyl-hydroxylases (PHDs) homologous to those acting as sensing components for the HIF system in animals occur in prokaryotes. We report cellular, biochemical, and crystallographic analyses revealing that Pseudomonas prolyl-hydroxylase domain containing protein (PPHD) contain a 2OG oxygenase related in structure and function to the animal PHDs. A Pseudomonas aeruginosa PPHD knockout mutant displays impaired growth in the presence of iron chelators and increased production of the virulence factor pyocyanin. We identify elongation factor Tu (EF-Tu) as a PPHD substrate, which undergoes prolyl-4-hydroxylation on its switch I loop. A crystal structure of PPHD reveals striking similarity to human PHD2 and a Chlamydomonas reinhardtii prolyl-4-hydroxylase. A crystal structure of PPHD complexed with intact EF-Tu reveals that major conformational changes occur in both PPHD and EF-Tu, including a >20-Å movement of the EF-Tu switch I loop. Comparison of the PPHD structures with those of HIF and collagen PHDs reveals conservation in substrate recognition despite diverse biological roles and origins. The observed changes will be useful in designing new types of 2OG oxygenase inhibitors based on various conformational states, rather than active site iron chelators, which make up most reported 2OG oxygenase inhibitors. Structurally informed phylogenetic analyses suggest that the role of prolyl-hydroxylation in human hypoxia sensing has ancient origins.

Properties of capsaicinoids for the control of fungi and oomycetes pathogenic to pepper

Capsaicinoids are pungent compounds found in pepper (Capsicum spp.) fruits. Capsaicin showed antimicrobial activity in plate assays against seven isolates of five species of fungi and nine isolates of two species of oomycetes. The general trend was that oomycetes were more inhibited than fungi. Assays of capsaicin biosynthetic precursors suggest that the lateral chain of capsaicinoids has more inhibitory activity than the phenolic part. In planta tests of capsaicinoids (capsaicin and N-vanillylnonanamide) applied to the roots demonstrated that these compounds conferred protection against the pathogenic fungus Verticillium dahliae and induced both chitinase activity and expression of several defence-related genes, such as CASC1, CACHI2 and CABGLU. N-Vanillylnonanamide infiltrated into cotyledons confers systemic protection to the upper leaves of pepper against the fungal pathogen Botrytis cinerea. In wild-type tomato plants such cotyledon infiltration has no protective effect, but is effective in the Never-ripe tomato mutant impaired in ethylene response. A similar effect was observed in tomato after salicylic acid infiltration.

Cigarette smoke enhances chemotaxis via acetylation of proline-glycine-proline

Several chronic lung diseases have been linked to cigarette smoking (Chronic Obstructive Pulmonary Disease (COPD), and cancer are associated with increased tobacco use). We recently described a collagen fragment, proline-glycine-proline (PGP), chemotactic for neutrophils, that appears to play a role in COPD, cystic fibrosis, and bronchiolitis obliterans syndrome. PGP can exist in either its native or acetylated form (NAcPGP), although the mechanism of N-terminal-acetylation remains unknown. This work investigates the possibility that cigarette smoke (CS) and its components acetylate PGP, describing a possible mechanism for some of the chronic inflammation seen in tobacco-associated disease. CSE and CSC (3.56 and 12.38 ng/ml NAcPGP respectively, p less than 0.01) and its components (acrolein, acetaldehyde, and methyl glyoxal) acetylated PGP (0.51, 1.03, and 0.23 ng/ml NAcPGP, p less than 0.01). Both N-acetyl-cysteine and carbocysteine (scavengers of reactive aldehydes) blocked chemical acetylation of PGP by CS (100 percent and 97 percent inhibition, respectively, p less than 0.01). NAcPGP is more chemoattractive to neutrophils, and less susceptible to degradation by Leukotriene-A4-Hydrolase (detected in the lung). These experiments propose a mechanism for the increased neutrophil recruitment seen in smoking-associated lung diseases.

Acetaminophen metabolism after major surgery: a greater challenge with increasing age

Patients undergoing major surgery represent a good model for the study of the hepatic metabolism of acetaminophen (APAP) after surgery and for the evaluation of how the detoxification process is influenced by aging. Thirty patients received intravenous APAP (1 g/6 h) for 4 days (D1-D4). Daily 24-h urinary metabolites-cysteine-APAP, mercapturate-APAP, APAP, and glucuronide and sulfate conjugates-as well as blood glutathione levels were compared with repeated-measures analysis of variance (significance, P<0.05). Between D1 and D4, cysteine-APAP increased (308±308 mg vs. 570±512 mg, P=0.005), and sulfate and glucuronide conjugates decreased (1,365±1,084 mg vs. 694±600 mg, P<0.0001 and 2,418±817 mg vs. 1,513±1,076 mg, P=0.011, respectively). Blood glutathione decreased (790±125 vs. 623±132 µmol/l, P<0.0001. These changes increased with aging. APAP disposition after major surgery shifts toward the oxidative pathways of metabolism, and this is enhanced with aging. Supplementation with sulfur-containing amino acids should be investigated further as it might minimize the effect on antioxidant defenses, especially in older persons undergoing more extensive surgical procedures.

Glutathione modulates the toxicity of, but is not a biologically relevant reductant for, the Pseudomonas aeruginosa redox toxin pyocyanin

Pyocyanin is an important redox toxin produced by the common human pathogen Pseudomonas aeruginosa. It generates reactive oxygen species (ROS) that alter intracellular redox status and cell function. Reducing equivalents for pyocyanin are provided by intracellular NAD(P)H and, it has been reported, glutathione (GSH). Cellular GSH levels are at least 1-2 orders of magnitude greater than NAD(P)H; therefore GSH should represent the major reductant for pyocyanin and potentiate its toxicity. Paradoxically, GSH has been found to inhibit pyocyanin toxicity in cellular models. This study was undertaken to evaluate the potential of GSH as a biologically relevant reductant for pyocyanin. As observed using spectrophotometry, under aerobic conditions pyocyanin readily oxidized NADPH, whereas oxidation of GSH could not be detected. Under anaerobic conditions pyocyanin was reduced by NADPH, but reduction by GSH could not be detected. Reduction of molecular oxygen and the formation of ROS readily proceeded in the presence of pyocyanin and NADPH, whereas GSH was without effect. Finally, exposure of normal human dermal fibroblasts to subcytotoxic concentrations of pyocyanin did not lead to depletion of endogenous GSH, but exogenous GSH provided protection against the senescence-inducing effects of the toxin. In summary, GSH does not reduce pyocyanin under physiologically relevant conditions or contribute to pyocyanin toxicity. However, GSH does provide protection against the deleterious effects of this important bacterial toxin on mammalian cells.