Production of leukotriene B4 and 5-hydroxyeicosatetraenoic acid by human neutrophils is inhibited by Pseudomonas aeruginosa phenazine derivatives

A biomedical perspective of pyocyanin from Pseudomonas aeruginosa: its applications and challenges

Pyocyanin is a bioactive pigment produced by Pseudomonas aeruginosa. It is an important virulence factor that plays a critical role in P. aeruginosa infections as a redox-active secondary metabolite and a quorum sensing (QS) signaling molecule. Pyocyanin production from chorismic acid requires the involvement of two homologous operons, phz1 and phz2, which are activated by QS regulatory proteins. Pyocyanin inhibits the proliferation of bacterial, fungal, and mammalian cells by inducing oxidative stress due to which it acts as a potent antibacterial, antifungal, and anticancer agent. Its potential role as a neuroprotectant needs further exploration. However, pyocyanin exacerbates the damaging effects of nosocomial infections caused by P. aeruginosa in immunocompromised individuals. Further, cystic fibrosis (CF) patients are highly susceptible to persistent P. aeruginosa infections in the respiratory system. The bacterial cells form colonies and three interconnected QS networks-pqs, las, and rhl-get activated, thus stimulating the cells to produce pyocyanin which exacerbates pulmonary complications. As an opportunistic pathogen, P. aeruginosa produces pyocyanin to impede the recovery of injuries like burn wounds through its anti-proliferative activity. Moreover, pyocyanin plays a vital role in compounding P. aeruginosa infections by promoting biofilm formation. This review begins with a brief description of the characteristics of pyocyanin, its activity, and the different aspects of its production including its biosynthesis, the role of QS, and the effect of environmental factors. It then goes on to explore the potential applications of pyocyanin as a biotherapeutic molecule while also highlighting the biomedical challenges and limitations that it presents.

Mechanistic insights into 5-lipoxygenase inhibition by pyocyanin: a molecular docking and molecular dynamics study

Pyocyanin, a redox-active phenazine pigment produced by Pseudomonas aeruginosa, inhibits 5-lipoxygenase (5-LOX) activity. However, whether pyocyanin can directly block the enzymatic activity by binding at the active site still remains a question because of its ability to produce superoxide radicals and H₂O₂. With the objective of characterizing this mechanism, we carried out molecular docking and molecular dynamics simulations and performed Molecular Mechanics Poisson-Boltzmann surface area (MMPBSA) binding energy studies. The results of the study revealed that pyocyanin is dynamically stable at the active site of 5-LOX and its MMPBSA binding energy (-84.720 kJ/mol) is comparable to that of the 5-LOX standard inhibitor zileuton (-72.729 kJ/mol). Similar studies using three other phenazine derivatives - 1-hydroxyphenazine, phenazine-1-carboxylic acid and phenazine-1-carboxamide - also showed encouraging results. In light of this evidence, we postulate as a proof of concept that pyocyanin and these phenazine derivatives have the potential to inhibit 5-LOX activity by directly binding at the active site and blocking enzymatic catalysis of the substrate. Considering the potential of 5-LOX inhibitors in inflammatory diseases such as asthma and rheumatoid arthritis, the findings of this study open up the exploration of phenazine derivatives in structure-based drug design against 5-LOX. Communicated by Ramaswamy H. Sarma.

Chronic Infections: A Possible Scenario for Autophagy and Senescence Cross-Talk

Multiple tissues and systems in the organism undergo modifications during aging due to an accumulation of damaged proteins, lipids, and genetic material. To counteract this process, the cells are equipped with specific mechanisms, such as autophagy and senescence. Particularly, the immune system undergoes a process called immunosenescence, giving rise to a chronic inflammatory status of the organism, with a decreased ability to counteract antigens. The obvious result of this process is a reduced defence capacity. Currently, there is evidence that some pathogens are able to accelerate the immunosenescence process for their own benefit. Although to date numerous reports show the autophagy–senescence relationship, or the connection between pathogens with autophagy or senescence, the link between the three actors remains unexplored. In this review, we have summarized current knowledge about important issues related to aging, senescence, and autophagy.

Paradoxical Role of 3-Methyladenine in Pyocyanin-Induced Toxicity in 1321N1 Astrocytoma and SH-SY5Y Neuroblastoma Cells

The role of autophagy in pyocyanin (PCN)-induced toxicity in the central nervous system (CNS) remains unclear, with only evidence from our group identifying it as a mechanism underlying toxicity in 1321N1 astrocytoma cells. Therefore, the aim of this study was to further examine the role of autophagy in PCN-induced toxicity in the CNS. To achieve this, we exposed 1321N1 astrocytoma and SH-SY5Y neuroblastoma cells to PCN (0-100 μmol/L) and tested the contribution of autophagy by measuring the impact of the autophagy inhibitor 3-methyladenine (3-MA) using a series of biochemical and molecular markers. Pretreatment of 1321N1 astrocytoma cells with 3-MA (5 mmol/L) decreased the PCN-induced acidic vesicular organelle and autophagosome formation as measured using acridine orange and green fluorescent protein-LC3 -LC3 fluorescence, respectively. Furthermore, 3-MA (5 mmol/L) significantly protected 1321N1 astrocytoma cells against PCN-induced toxicity. In contrast pretreatment with 3-MA (5 mmol/L) increased PCN-induced toxicity in SH-SY5Y neuroblastoma cells. Given the influence of autophagy in inflammatory responses, we investigated whether the observed effects in this study involved inflammatory mediators. The PCN (100 μmol/L) significantly increased the production of interleukin-8 (IL-8), prostaglandin E2 (PGE2), and leukotriene B4 (LTB4) in both cell lines. Consistent with its paradoxical role in modulating PCN-induced toxicity, 3-MA (5 mmol/L) significantly reduced the PCN-induced production of IL-8, PGE2, and LTB4 in 1321N1 astrocytoma cells but augmented their production in SH-SY5Y neuroblastoma cells. In conclusion, we show here for the first time the paradoxical role of autophagy in mediating PCN-induced toxicity in 1321N1 astrocytoma and SH-SY5Y neuroblastoma cells and provide novel evidence that these actions may be mediated by effects on IL-8, PGE2, and LTB4 production.

Redox warfare between airway epithelial cells and Pseudomonas: dual oxidase versus pyocyanin

The importance of reactive oxygen species-dependent microbial killing by the phagocytic cell NADPH oxidase has been appreciated for some time, although only recently has an appreciation developed for the partnership of lactoperoxidase with related dual oxidases (Duox) within secretions of the airway surface layer. This system produces mild oxidants designed for extracellular killing that are effective against several airway pathogens, including Staphylococcus aureus, Burkholderia cepacia, and Pseudomonas aeruginosa. Establishment of chronic pseudomonas infections involves adaptations to resist oxidant-dependent killing by expression of a redox-active virulence factor, pyocyanin, that competitively inhibits epithelial Duox activity by consuming intracellular NADPH and producing superoxide, thereby inflicting oxidative stress on the host.

Pseudomonas pyocyanin inhibits wound repair by inducing premature cellular senescence: role for p38 mitogen-activated protein kinase

Pseudomonas aeruginosa is an important nosocomial pathogen of burn wounds. Pyocyanin, a virulence factor produced by the bacterium, induces persistent intracellular oxidative stress and premature senescence in mammalian cells. Our aims were to evaluate pyocyanin levels in infected wound dressings and the potential of the toxin to influence wound repair. Surgical dressings from infected burn patients were examined for pyocyanin and normal primary human diploid fibroblasts (HDFs) were treated with comparable concentrations and their replicative ability examined. Pyocyanin was detected in the exudate of infected wound dressings in amounts up to 5.3 microg/g (mean: 2.0+/-2.3 microg/g). HDFs exposed to pyocyanin (1-50 microM; 0.2-10.5 microg/ml) underwent growth arrest at all concentrations and developed morphological characteristics associated with cellular senescence, including expression of senescence-associated beta-galactosidase. Using an in vitro wound repair model, a single exposure to pyocyanin inhibited wound repair in a concentration-dependent manner. Prior treatment with a specific p38(MAPK) inhibitor allowed cells to maintain their replicative ability and pre-senescent morphology indicating pyocyanin operates through the Erk/p38(MAPK) senescence pathway. These data support the hypothesis that bacterial virulence factors capable of inducing persistent low-level oxidative stress play a pivotal role in modulating the tissue repair response to infection by inducing premature cellular senescence.

Premature cellular senescence induced by pyocyanin, a redox-active Pseudomonas aeruginosa toxin

Pseudomonas aeruginosa is an important nosocomial pathogen that can cause acute and chronic infection, particularly of the respiratory system. Pyocyanin is a major P. aeruginosa virulence factor that displays redox activity and induces oxidative stress in cellular systems. The effect of pyocyanin on replicating human pulmonary epithelial (A549) cells was investigated. Cells were exposed to pyocyanin for 24 h and their subsequent growth and development were followed for 7 days. Pyocyanin (5-10 microM) arrested cell growth and resulted in the development of a morphological phenotype consistent with cellular senescence, that is, an enlarged and flattened appearance. The senescent nature of these cells was supported by positive staining for increased lysosomal content and senescence-associated beta-galactosidase activity. All cells treated with pyocyanin (10 microM) converted to the senescent phenotype, which remained stable for up to 7 days. Exposure to pyocyanin at 25 microM or greater resulted in cell death due to apoptosis. A549 cells exposed to pyocyanin generated hydrogen peroxide in a dose-dependent manner and the senescence-inducing effect of pyocyanin was inhibited by the antioxidant, glutathione, suggesting the involvement of reactive oxygen species. The induction of premature cellular senescence by redox-active bacterial toxins may be a hitherto unrecognized aspect of infection pathology and a limiting factor in the tissue repair response to infection.

Pyocyanin induces oxidative stress in human endothelial cells and modulates the glutathione redox cycle

Pyocyanin is a redox active virulence factor produced by the human pathogen Pseudomonas aeruginosa. Treatment of endothelial cells with pyocyanin (1-50 microM) resulted in the dose-dependent formation of hydrogen peroxide that was detected in the extracellular medium. Total intracellular glutathione levels decreased in response to pyocyanin in a dose-dependent manner from a control value of 19.9 +/- 2.7 nmol/mg protein to 10.0 +/- 2.4 nmol/mg protein. Prior treatment of cells with catalase afforded complete protection against loss of glutathione. Total intracellular soluble thiols decreased from 95.0 +/- 6.2 nmol/mg protein to 78.6 +/- 2.3 nmol/mg protein at the highest test dose. Intracellular levels of NADPH increased up to 2.4-fold in response to pyocyanin exposure. It is concluded that pyocyanin exposes endothelial cells to oxidative stress by the generation of hydrogen peroxide, which subsequently depletes intracellular glutathione and increases intracellular levels of mixed disulfides.

Short-term regulation of basolateral organic anion uptake in proximal tubular OK cells: EGF acts via MAPK, PLA(2), and COX1

The organic anion transport system of the kidney is of major importance for the excretion of a variety of endogenous compounds, drugs, and potentially toxic substances. The basolateral uptake into proximal tubular cells is mediated by a tertiary active transport system. Epidermal growth factor (EGF) leads to an increase in the basolateral uptake rate of the model substrate para-aminohippuric acid (PAH) in opossum kidney (OK) cells. This stimulation is mediated by successive activation of the mitogen-activated protein kinases,mitogen-activated/extracellular signal-regulated kinase kinase (MEK) and extracellular regulated kinase isoforms 1 and 2 (ERK1/2). This study investigates the regulatory network of EGF action on PAH uptake downstream ERK1/2 in more detail. EGF stimulation of the basolateral uptake rate of [(14)C]PAH was abolished by the phospholipase A(2) inhibitor AACOCF3.[(14)C]PAH uptake was enhanced by arachidonic acid. Furthermore, EGF led to an increase in arachidonic acid release and to the generation of prostaglandins. AACOCF3 did not influence EGF-induced ERK1/2 activation, indicating that ERK1/2 is upstream of PLA(2). In addition, EGF stimulated the influx of extracellular Ca(2+). However, Ca(2+)-influx was not required for the stimulatory action of EGF on [(14)C]PAH uptake. Inhibitors of COX and lipoxygenases reduced [(14)C]PAH uptake dose-dependently, whereas inhibition of cytochrome P450 did not. In the presence of indomethacin, EGF had no stimulatory effect on [(14)C]PAH uptake. The inhibitory effect of indomethacin was not due to competitive action on PAH uptake. Furthermore, prostaglandin E(2) (PGE(2)) increased basolateral [(14)C]PAH uptake rate dose-dependently, and this increase was also observed in the presence of indomethacin. Selective inhibition of COX2 by indomethacin amid or indomethacin n-heptyl ester did not inhibit [(14)C]PAH uptake, whereas selective inhibition of COX1 dose-dependently inhibited [(14)C]PAH uptake. This and previous data lead to the conclusion that EGF successively activates MEK, ERK1/2, and PLA(2), leading to an increased release of arachidonic acid. Subsequently, arachidonic acid is metabolized to prostaglandins via COX1, which then mediate EGF-induced stimulation of basolateral organic anion uptake rate.

Modulation of neutrophil superoxide response and intracellular diacylglyceride levels by the bacterial pigment pyocyanin

Low concentrations of pyocyanin are reported to enhance superoxide production by human neutrophils exposed to various stimuli, yet the mechanism remains unknown. Using lucigenin-enhanced chemiluminescence, we examined the kinetics of the neutrophil superoxide response in the presence of pyocyanin. At all concentrations (12.5 to 200 microM), pyocyanin decreased the peak superoxide response while prolonging the duration of the response. The prolonged response may be associated with an observed increase in intracellular diacylglyceride levels due to pyocyanin exposure.

Role of oxidants in microbial pathophysiology

Reactive oxidant species (superoxide, hydrogen peroxide, hydroxyl radical, hypohalous acid, and nitric oxide) are involved in many of the complex interactions between the invading microorganism and its host. Regardless of the source of these compounds or whether they are produced under normal conditions or those of oxidative stress, these oxidants exhibit a broad range of toxic effects to biomolecules that are essential for cell survival. Production of these oxidants by microorganisms enables them to have a survival advantage in their environment. Host oxidant production, especially by phagocytes, is a counteractive mechanism aimed at microbial killing. However, this mechanism may be contribute to a deleterious consequence of oxidant exposure, i.e., inflammatory tissue injury. Both the host and the microorganism have evolved complex adaptive mechanisms to deflect oxidant-mediated damage, including enzymatic and nonenzymatic oxidant-scavenging systems. This review discusses the formation of reactive oxidant species in vivo and how they mediate many of the processes involved in the complex interplay between microbial invasion and host defense.

Scavenging of neutrophil-derived superoxide anion by 1-hydroxyphenazine, a phenazine derivative associated with chronic Pseudomonas aeruginosa infection: relevance to cystic fibrosis

The airways of cystic fibrosis patients colonised by Pseudomonas aeruginosa contain the redox active phenazine derivative, 1-hydroxyphenazine (OHP). As the presence of reactive oxygen species is of importance to tissue damage in cystic fibrosis, OHP was investigated for its ability to reduce molecular oxygen to superoxide. In the presence of NADPH, OHP reduced cytochrome c in a dose-dependent manner. This effect was not inhibited by superoxide dismutase and demonstrates an electron transport role for OHP. The OHP/NADPH system was unable to reduce molecular oxygen to superoxide as judged by an inability to oxidase epinephrine to adrenochrome. However, using lucigenin-enhanced chemiluminescence to detect superoxide, it was found that pathophysiologically relevant concentrations of OHP (5-25 microM) effectively scavenged superoxide from a xanthine/xanthine oxidase system. Similarly, in the presence of OHP, superoxide availability from contact-activated neutrophils was substantially reduced. It is concluded that OHP is an efficient scavenger of superoxide and that electron transfer from superoxide to OHP represents a major mechanism for reduction of OHP in vivo. Reduced OHP has the potential to alter cellular function by participating in the reduction of iron-containing proteins and in this manner contribute to the pathogenesis of P. aeruginosa infection in cystic fibrosis.

Inhibition of the human platelet cyclooxygenase response by the naturally occurring phenazine derivative, 1-hydroxyphenazine

The phenazine derivative, 1-hydroxyphenazine (OHP), is produced in vivo by Pseudomonas aeruginosa, an organism that colonises the airways of patients with cystic fibrosis. While known to inhibit leukotriene production by human neutrophils, the effects of OHP on cyclooxygenase pathways have not previously been reported. We used [3H] arachidonic acid (AA) under conditions of concurrent labelling-stimulation or pre-labelling for one hour followed by stimulation to determine the effects of OHP on the production of cyclooxygenase metabolites by human platelets stimulated with the calcium ionophore, A23187. Thromboxane B2 (TxB2) and 12-hydroxyheptadecatrienoic acid (HHT) production was inhibited in a dose-dependent manner by OHP using either pre-labelled or concurrently labelled platelets. However, production of 12-hydroxyeicosatetraenoic acid (12-HETE) was not diminished. Determination of the amount of total free label (AA+non-esterified AA metabolites) after stimulation of pre-labelled platelets indicated a dose-dependent inhibition of the release of AA from phospholipid by OHP. This was reflected in a corresponding increase in phospholipid AA content. These data indicate that phenazine derivatives of bacterial origin exhibit complex interactions with pathways of arachidonic acid metabolism in host cells. These effects may prove to be of pharmacological importance.

Interaction of the Pseudomonas aeruginosa secretory products pyocyanin and pyochelin generates hydroxyl radical and causes synergistic damage to endothelial cells. Implications for Pseudomonas-associated tissue injury

Pyocyanin, a secretory product of Pseudomonas aeruginosa, has the capacity to undergo redox cycling under aerobic conditions with resulting generation of superoxide and hydrogen peroxide. By using spin trapping techniques in conjunction with electron paramagnetic resonance spectrometry (EPR), superoxide was detected during the aerobic reduction of pyocyanin by NADH or porcine endothelial cells. No evidence of hydroxyl radical formation was detected. Chromium oxalate eliminated the EPR spectrum of the superoxide-derived spin adduct resulting from endothelial cell exposure to pyocyanin, suggesting superoxide formation close to the endothelial cell plasma membrane. We have previously reported that iron bound to the P. aeruginosa siderophore pyochelin (ferripyochelin) catalyzes the formation of hydroxyl free radical from superoxide and hydrogen peroxide via the Haber-Weiss reaction. In the present study, spin trap evidence of hydroxyl radical formation was detected when NADH and pyocyanin were allowed to react in the presence of ferripyochelin. Similarly, endothelial cell exposure to pyocyanin and ferripyochelin also resulted in hydroxyl radical production which appeared to occur in close proximity to the cell surface. As assessed by 51Cr release, endothelial cells which were treated with pyocyanin or ferripyochelin alone demonstrated minimal injury. However, endothelial cell exposure to the combination of pyochelin and pyocyanin resulted in 55% specific 51Cr release. Injury was not observed with the substitution of iron-free pyochelin and was diminished by the presence of catalase or dimethyl thiourea. These data suggest the possibility that the P. aeruginosa secretory products pyocyanin and pyochelin may act synergistically via the generation of hydroxyl radical to damage local tissues at sites of pseudomonas infection.

Leukotriene B4 omega-oxidation by human polymorphonuclear leukocytes is inhibited by pyocyanin, a phenazine derivative produced by Pseudomonas aeruginosa

Human polymorphonuclear leukocytes (PMNL) metabolize the potent chemotaxin leukotriene B4 (LTB4) by omega-oxidation to 20-hydroxyl-LTB4 and 20-carboxy-LTB4. The ability of unstimulated human PMNL to metabolize exogenous LTB4 was found to be inhibited by pyocyanin, a phenazine derivative produced by Pseudomonas aeruginosa, in a dose-dependent manner. 1-Hydroxyphenazine (1-OHP), a metabolite of pyocyanin, was not inhibitory under identical conditions. The initial enzymic step in the conversion of LTB4 is catalyzed by an NADPH-dependent cytochrome, P-450. Reduction of the phenazine derivatives by NADPH was measured spectrophotometrically. Pyocyanin was reduced by NADPH in vitro in a pH-dependent manner, while 1-OHP was poorly or negligibly reduced under similar conditions. Formation of NADP+ was 20.3 +/- 1.8 nmol min-1 for pyocyanin (10 microM) at pH 5.5, compared with 0.6 +/- 0.2 nmol min-1 for 1-OHP (10 microM), while at pH 7.5 a value of 2.2 +/- 1.3 nmol min-1 was obtained for pyocyanin, with no detectable activity for 1-OHP. This indicates that inhibition of LTB4 omega-hydroxylase activity by pyocyanin might be achieved by competition for NADPH. Incorporation of exogenous 5-hydroxyeicosatetraenoic acid by PMNL into lipid pools was not affected by either phenazine derivative. The ability of bacterial pyocyanin to limit the omega-oxidation of LTB4 may have important implications for PMNL LTB4 receptor status and chemotaxis in vivo.

Bacterial metabolism of human polymorphonuclear leukocyte-derived arachidonic acid

Evidence for transcellular bacterial metabolism of phagocyte-derived arachidonic acid was sought by exposing human blood polymorphonuclear leukocytes, prelabelled with [3H]arachidonic acid, to opsonized, stationary-phase Pseudomonas aeruginosa (bacteria-to-phagocyte ratio of 50:1) for 90 min at 37 degrees C. Control leukocytes were stimulated with the calcium ionophore A23187 (5 microM) for 5 min. Radiochromatograms of arachidonic acid metabolites, extracted from A23187-stimulated cultures and then separated by reverse-phase high-performance liquid chromatography, revealed leukotriene B4, its omega-oxidation products, and 5-hydroxy-eicosatetraenoic acid. In contrast, two major metabolite peaks, distinct from known polymorphonuclear leukocyte arachidonic acid products by high-performance liquid chromatography or by thin-layer chromatography, were identified in cultures of P. aeruginosa with [3H]arachidonic acid-labelled polymorphonuclear leukocytes. Respective chromatographic characteristics of these novel products were identical to those of two major metabolite peaks produced by incubation of stationary-phase P. aeruginosa with [3H]arachidonic acid. Production of the metabolites was dependent upon pseudomonal viability. UV spectral data were consistent with a conjugated diene structure. Metabolism of arachidonic acid by P. aeruginosa was not influenced by the presence of catalase, superoxide dismutase, nordihydroguaiaretic acid, ethanol, dimethyl sulfoxide, or ferrous ions but was inhibited by carbon monoxide, ketoconazole, and 1,2-epoxy-3,3,3-trichloropropane. Our data suggest that pseudomonal metabolism of polymorphonuclear leukocyte-derived arachidonic acid occurs during phagocytosis, probably by enzymatic epoxidation and hydroxylation via an oxygenase. By this means, potential proinflammatory effects of arachidonic acid or its metabolites may be modulated by P. aeruginosa at sites of infection in vivo.