Induction of inflammatory mediators (histamine and leukotrienes) from rat peritoneal mast cells and human granulocytes by Pseudomonas aeruginosa strains from burn patients

Histone derived antimicrobial peptides identified from Mytilus coruscus serum by peptidomics

Histones and their N-terminal or C-terminal derived peptides have been studied in vertebrates and presented as potential antimicrobial agents playing important roles in the innate immune defenses. Although histones and their derived peptides had been reported as components of innate immunity in invertebrates, the knowledge about the histone derived antimicrobial peptides (HDAPs) in invertebrates are still limited. Using a peptidomic technique, a set of peptide fragments derived from the histones was identified in this study from the serum of microbes challenged Mytilus coruscus. Among the 85 identified histone-derived-peptides with high confidence, 5 HDAPs were chemically synthesized and the antimicrobial activities were verified, showing strong growth inhibition against Gram-positive bacteria, Gram-negative bacteria, and fungus. The gene expression level of the precursor histones matched by representative HDAPs were further tested using q-PCR, and the results showed a significant upregulation of the histone gene expression levels in hemocytes, gill, and mantle of the mussel after immune stress. In addition, three identified HDAPs were selected for preparation of specific antibodies, and the corresponding histones and their derived C-terminal fragments were detected by Western blotting in the blood cell and serum of immune challenged mussel, respectively, indicating the existence of HDAPs in M. coruscus. Our findings revealed the immune function of histones in Mytilus, and confirmed the existence of HDAPs in the mussel. The identified Mytilus HDAPs represent a new source of immune effector with antimicrobial function in the innate immune system, and thus provide promising candidates for the treatment of microbial infections in aquaculture and medicine.

GATR-3, a Peptide That Eradicates Preformed Biofilms of Multidrug-Resistant Acinetobacter baumannii

Acinetobacter baumannii is a gram-negative bacterium that causes hospital-acquired and opportunistic infections, resulting in pneumonia, sepsis, and severe wound infections that can be difficult to treat due to antimicrobial resistance and the formation of biofilms. There is an urgent need to develop novel antimicrobials to tackle the rapid increase in antimicrobial resistance, and antimicrobial peptides (AMPs) represent an additional class of potential agents with direct antimicrobial and/or host-defense activating activities. In this study, we present GATR-3, a synthetic, designed AMP that was modified from a cryptic peptide discovered in American alligator, as our lead peptide to target multidrug-resistant (MDR) A. baumannii. Antimicrobial susceptibility testing and antibiofilm assays were performed to assess GATR-3 against a panel of 8 MDR A. baumannii strains, including AB5075 and some clinical strains. The GATR-3 mechanism of action was determined to be via loss of membrane integrity as measured by DiSC3(5) and ethidium bromide assays. GATR-3 exhibited potent antimicrobial activity against all tested multidrug-resistant A. baumannii strains with rapid killing. Biofilms are difficult to treat and eradicate. Excitingly, GATR-3 inhibited biofilm formation and, more importantly, eradicated preformed biofilms of MDR A. baumannii AB5075, as evidenced by MBEC assays and scanning electron micrographs. GATR3 did not induce resistance in MDR A. baumannii, unlike colistin. Additionally, the toxicity of GATR-3 was evaluated using human red blood cells, HepG2 cells, and waxworms using hemolysis and MTT assays. GATR-3 demonstrated little to no cytotoxicity against HepG2 and red blood cells, even at 100 μg/mL. GATR-3 injection showed little toxicity in the waxworm model, resulting in a 90% survival rate. The therapeutic index of GATR-3 was estimated (based on the HC50/MIC against human RBCs) to be 1250. Overall, GATR-3 is a promising candidate to advance to preclinical testing to potentially treat MDR A. baumannii infections.

An Organ System-Based Synopsis of Pseudomonas aeruginosa Virulence

Driven in part by its metabolic versatility, high intrinsic antibiotic resistance, and a large repertoire of virulence factors, Pseudomonas aeruginosa is expertly adapted to thrive in a wide variety of environments, and in the process, making it a notorious opportunistic pathogen. Apart from the extensively studied chronic infection in the lungs of people with cystic fibrosis (CF), P. aeruginosa also causes multiple serious infections encompassing essentially all organs of the human body, among others, lung infection in patients with chronic obstructive pulmonary disease, primary ciliary dyskinesia and ventilator-associated pneumonia; bacteremia and sepsis; soft tissue infection in burns, open wounds and postsurgery patients; urinary tract infection; diabetic foot ulcers; chronic suppurative otitis media and otitis externa; and keratitis associated with extended contact lens use. Although well characterized in the context of CF, pathogenic processes mediated by various P. aeruginosa virulence factors in other organ systems remain poorly understood. In this review, we use an organ system-based approach to provide a synopsis of disease mechanisms exerted by P. aeruginosa virulence determinants that contribute to its success as a versatile pathogen.

Histamine activates HinK to promote the virulence of Pseudomonas aeruginosa

During infections, bacteria stimulate host cells to produce and release histamine, which is a key mediator of vital cellular processes in animals. However, the mechanisms underlying the bacterial cell's ability to sense and respond to histamine are poorly understood. Herein, we show that HinK, a LysR-type transcriptional regulator, is required to evoke responses to histamine in Pseudomonas aeruginosa, an important human pathogen. HinK directly binds to and activates the promoter of genes involved in histamine uptake and metabolism, iron acquisition, and Pseudomonas quinolone signal (PQS) biosynthesis. The transcriptional regulatory activity of HinK is induced when histamine is present, and it occurs when HinK binds with imidazole-4-acetic acid (ImAA), a histamine metabolite whose production in P. aeruginosa depends on the HinK-activated histamine uptake and utilization operon hinDAC-pa0222. Importantly, the inactivation of HinK inhibits diverse pathogenic phenotypes of P. aeruginosa. These results suggest that histamine acts as an interkingdom signal and provide insights into the mechanism used by pathogenic bacteria to exploit host regulatory signals to promote virulence.

Rhamnolipid the Glycolipid Biosurfactant: Emerging trends and promising strategies in the field of biotechnology and biomedicine

Rhamnolipids (RLs) are surface-active compounds and belong to the class of glycolipid biosurfactants, mainly produced from Pseudomonas aeruginosa. Due to their non-toxicity, high biodegradability, low surface tension and minimum inhibitory concentration values, they have gained attention in various sectors like food, healthcare, pharmaceutical and petrochemicals. The ecofriendly biological properties of rhamnolipids make them potent materials to be used in therapeutic applications. RLs are also known to induce apoptosis and thus, able to inhibit proliferation of cancer cells. RLs can also act as immunomodulators to regulate the humoral and cellular immune systems. Regarding their antimicrobial property, they lower the surface hydrophobicity, destruct the cytoplasmic membrane and lower the critical micelle concentration to kill the bacterial cells either alone or in combination with nisin possibly due to their role in modulating outer membrane protein. RLs are also involved in the synthesis of nanoparticles for in vivo drug delivery. In relation to economic benefits, the post-harvest decay of food can be decreased by RLs because they prevent the mycelium growth, spore germination of fungi and inhibit the emergence of biofilm formation on food. The present review focuses on the potential uses of RLs in cosmetic, pharmaceutical, food and health-care industries as the potent therapeutic agents.

Targeting cystic fibrosis inflammation in the age of CFTR modulators: focus on macrophages

Cystic fibrosis (CF) is a life-shortening, multi-organ, autosomal recessive disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The most prominent clinical manifestation in CF is the development of progressive lung disease characterised by an intense, chronic inflammatory airway response that culminates in respiratory failure and, ultimately, death. In recent years, a new class of therapeutics that have the potential to correct the underlying defect in CF, known as CFTR modulators, have revolutionised the field. Despite the exciting success of these drugs, their impact on airway inflammation, and its long-term consequences, remains undetermined. In addition, studies querying the absolute requirement for infection as a driver of CF inflammation have challenged the traditional consensus on CF pathogenesis, and also emphasise the need to prioritise complementary anti-inflammatory treatments in CF. Macrophages, often overlooked in CF research despite their integral role in other chronic inflammatory pathologies, have increasingly become recognised as key players in the initiation, perpetuation and resolution of CF lung inflammation, perhaps as a direct result of CFTR dysfunction. These findings suggest that macrophages may be an important target for novel anti-inflammatory interventional strategies to effectively treat CF lung function decline. This review will consider evidence for the efficacy of anti-inflammatory drugs in the treatment of CF, the potential role of macrophages, and the significance of targeting these pathways at a time when rectifying the basic defect in CF, through use of novel CFTR modulator therapies, is becoming increasingly viable.

In vitro study of virulence potential of Acinetobacter baumannii outer membrane vesicles

Acinetobacter baumannii has emerged as an important opportunistic pathogen mostly causing nosocomial infections. The virulence factors of this important pathogen are largely unknown. Outer membrane vesicles (OMV) are naturally secreted by many gram negative and gram positive bacteria. These vesicles contain outer membrane proteins, lipids, periplasmic proteins, DNA and RNA. Their role in intracellular and intercellular signaling, transfer of virulence factors and eliciting immune response in host cells has been established in many pathogens. In this study, we investigated OMVs from three multi-drug resistant (MDR) clinical isolates and a non-MDR reference strain of A. baumannii for virulence potential. A. baumannii OMVs showed phospholipase C, hemolytic and leukotoxic activities. We found large variations in virulence potential between OMVs of MDR clinical isolates and non-MDR reference strain. These effector molecules were concentrated in OMVs than whole cell bacterial culture and cell-free supernatant. OMV-mediated phospholipase, hemolytic and leucotoxic activities may have a key role in pathogenicity of A. baumannii infection and may be future targets for therapeutic and preventive strategies. This is, to the best of our knowledge, the first report showing virulence potential of A. baumannii OMVs.

A randomized double blind, placebo controlled phase 2 trial of BIIL 284 BS (an LTB4 receptor antagonist) for the treatment of lung disease in children and adults with cystic fibrosis

BACKGROUND

Airway inflammation, mediated in part by LTB4, contributes to lung destruction in patients with cystic fibrosis (CF). LTB(4)-receptor inhibition may reduce airway inflammation. We report the results of a randomized, double-blind, placebo-controlled study of the efficacy and safety of the leukotriene B(4) (LTB(4))-receptor antagonist BIIL 284 BS in CF patients.

METHODS

CF patients aged ≥6 years with mild to moderate lung disease were randomized to oral BIIL 284 BS or placebo once daily for 24 weeks. Co-primary endpoints were change in FEV(1) and incidence of pulmonary exacerbation.

RESULTS

After 420 (155 children, 265 adults) of the planned 600 patients were randomized, the trial was terminated after a planned interim analysis revealed a significant increase in pulmonary related serious adverse events (SAEs) in adults receiving BIIL 284 BS. Final analysis revealed SAEs in 36.1% of adults receiving BIIL 284 BS vs. 21.2% receiving placebo (p = 0.007), and in 29.6% of children receiving BIIL 284 BS vs. 22.9% receiving placebo (p = 0.348). In adults, the incidence of protocol-defined pulmonary exacerbation was greater in those receiving BIIL 284 BS than in those receiving placebo (33.1% vs. 18.2% respectively; p = 0.005). In children, the incidence of protocol-defined pulmonary exacerbation was 19.8% in the BIIL 284 BS arm, and 25.7% in the placebo arm (p = 0.38).

CONCLUSIONS

While the cause of increased SAEs and exacerbations due to BIIL 284 BS is unknown, the outcome of this trial provides a cautionary tale for the administration of potent anti-inflammatory compounds to individuals with chronic infections, as the potential to significantly suppress the inflammatory response may increase the risk of infection-related adverse events.

Transcranial magnetic stimulation can diagnose electrical burn-induced myelopathy

INTRODUCTION

We conducted motor- and sensory-evoked potential analyses and investigated their diagnostic value in differentiating between electrical burns without evidence of neurologic injury and those with clinical evidence of myelopathy.

METHODS

We studied high-voltage electrical burn injury patients with lower extremity weakness and evidence of myelopathy and those without any evidence of neurological complications. Motor-evoked potentials (MEPs), somatosensory-evoked potentials (SEPs), and MRI studies of the spinal cord, as well as transcranial magnetic stimulations, were performed. The central motor conduction time (CMCT) was also calculated.

RESULTS

The upper limb MEP and upper and lower limb SEP variables did not statistically differ between the 2 groups. The CMCT and total motor conduction time recorded in the lower limb were delayed in the burn myelopathy group. MRI revealed no abnormal signal changes in myelopathy patients.

CONCLUSION

Our study demonstrates that MEP is useful in identifying myelopathy in patients who have sustained high-voltage electrical burns.

The mast cell in innate and adaptive immunity

Mast cells (MCs) were once considered only as effector cells in pathogenic IgE- and IgG-mediated responses such as allergy. However, developments over the last 15 years have suggested that MCs have evolved in vertebrates as beneficial effector cells that are involved in the very first inflammatory responses generated during infection. This pro-inflammatory environment has been demonstrated to be important for initiating innate responses in many different models of infection and more recently, in the development of adaptive immunity as well. Interestingly this latter finding has led to the discovery that small MC-activating compounds can behave as adjuvants in vaccine formulations. Thus, our continued understanding of the MC in the context of infectious disease is likely to not only expand our scope of the MC in the normal processes of immunity, but provide new therapeutic targets to combat disease.

A new class of human mast cell and peripheral blood basophil stabilizers that differentially control allergic mediator release

Treatments for allergic disease block the effects of mediators released from activated mast cells and blood basophils. A panel of fullerene derivatives was synthesized and tested for their ability to preempt the release of allergic mediators in vitro and in vivo. The fullerene C(70)-tetraglycolic acid significantly inhibited degranulation and cytokine production from mast cells and basophils, while C(70)-tetrainositol blocked only cytokine production in mast cells and degranulation and cytokine production in basophils. The early phase of FcepsilonRI inhibition was dependent on the blunted release of intracellular calcium stores, elevations in reactive oxygen species, and several signaling molecules. Gene microarray studies further showed the two fullerene derivatives inhibited late phase responses in very different ways. C(70)-tetraglycolic acid was able to block mast cell-driven anaphylaxis in vivo, while C(70)-tetrainositol did not. No toxicity was observed with either compound. These findings demonstrate the biological effects of fullerenes critically depends on the moieties added to the carbon cage and suggest they act on different FcepsilonRI-specific molecules in mast cells and basophils. These next generation fullerene derivatives represent a new class of compounds that interfere with FcepsilonRI signaling pathways to stabilize mast cells and basophils. Thus, fullerene-based therapies may be a new approach for treating allergic diseases.

Rhamnolipids: diversity of structures, microbial origins and roles

Rhamnolipids are glycolipidic biosurfactants produced by various bacterial species. They were initially found as exoproducts of the opportunistic pathogen Pseudomonas aeruginosa and described as a mixture of four congeners: alpha-L-rhamnopyranosyl-alpha-L-rhamnopyranosyl-beta-hydroxydecanoyl-beta-hydroxydecanoate (Rha-Rha-C(10)-C(10)), alpha-L-rhamnopyranosyl-alpha-L-rhamnopyranosyl-beta-hydroxydecanoate (Rha-Rha-C(10)), as well as their mono-rhamnolipid congeners Rha-C(10)-C(10) and Rha-C(10). The development of more sensitive analytical techniques has lead to the further discovery of a wide diversity of rhamnolipid congeners and homologues (about 60) that are produced at different concentrations by various Pseudomonas species and by bacteria belonging to other families, classes, or even phyla. For example, various Burkholderia species have been shown to produce rhamnolipids that have longer alkyl chains than those produced by P. aeruginosa. In P. aeruginosa, three genes, carried on two distinct operons, code for the enzymes responsible for the final steps of rhamnolipid synthesis: one operon carries the rhlAB genes and the other rhlC. Genes highly similar to rhlA, rhlB, and rhlC have also been found in various Burkholderia species but grouped within one putative operon, and they have been shown to be required for rhamnolipid production as well. The exact physiological function of these secondary metabolites is still unclear. Most identified activities are derived from the surface activity, wetting ability, detergency, and other amphipathic-related properties of these molecules. Indeed, rhamnolipids promote the uptake and biodegradation of poorly soluble substrates, act as immune modulators and virulence factors, have antimicrobial activities, and are involved in surface motility and in bacterial biofilm development.

Selective early production of CCL20, or macrophage inflammatory protein 3alpha, by human mast cells in response to Pseudomonas aeruginosa

Mast cells are important as sentinel cells in host defense against bacterial infection. Much of their effectiveness depends upon recruiting other immune cells; however, little is known about the mechanisms of this response. CCL20, also known as macrophage inflammatory protein-3alpha (MIP-3alpha), Exodus, and LARC, is a chemokine known to be a potent chemoattractant for immature dendritic cells and T cells. In this study, we examined the human mast cell production of both CCL20 and granulocyte-macrophage colony-stimulating factor (GM-CSF), a critical cytokine for innate immune responses in the lung, in response to Pseudomonas aeruginosa. Reverse transcription-PCR and Western blot analysis demonstrated that the human mast cells (HMC-1) express CCL20 mRNA and are able to produce a significant amount (32.4 ng/ml) of CCL20 protein following stimulation by calcium ionophore and phorbol myristate acetate. Importantly, P. aeruginosa potently stimulated CCL20 production in human cord blood-derived mast cells (CBMC), with production peaking at 6 h after stimulation. This time course of expression was distinct from that of GM-CSF, which peaked after 24 to 48 h. Significant CCL20 production did not occur following immunoglobulin E-mediated activation of CBMC under conditions which induced a substantial GM-CSF response. Interestingly, the CCL20 response of mast cells to P. aeruginosa was relatively resistant to inhibition by the corticosteroid dexamethasone, interleukin-10, or cyclosporine, while GM-CSF production was potently inhibited. However, P. aeruginosa-induced CCL20 production was blocked by the protein kinase C (PKC) inhibitor Ro 31-8220 and a PKC pseudosubstrate. These results support a role for human mast cells in the initiation of immune responses to P. aeruginosa infection.

Pseudomonas aeruginosa activates human mast cells to induce neutrophil transendothelial migration via mast cell-derived IL-1 alpha and beta

The mechanisms of neutrophil (PMN) recruitment to Pseudomonas aeruginosa infection remain incompletely defined. Mast cells (MC) involvement in this process has not been studied previously. In this study, we demonstrate that human cord blood-derived MC phagocytose P. aeruginosa and release mediators that activate HUVEC monolayers for supporting PMN transmigration. Pretreatment of supernatants from P. aeruginosa-MC cocultures with neutralizing anti-IL-1alpha plus anti-IL-1beta Abs, or IL-1R antagonist before addition to HUVEC for stimulation completely abrogated MC-induced PMN transmigration, while anti-TNF-alpha treatment had no effect. The expression of E-selectin and ICAM-1 on HUVEC, the latter a ligand for PMN CD11/CD18, was significantly up-regulated by P. aeruginosa-induced MC mediators. Pretreatment of human PMN with anti-CD18 mAb or pretreatment of HUVEC with a combination of three mAbs (against ICAM-1, ICAM-2, and E-selectin) inhibited by 85% the MC-dependent PMN transmigration. Moreover, P. aeruginosa-induced production of IL-1alpha and IL-1beta was down-regulated by IL-10 and dexamethasone. This study demonstrates for the first time that MC may mediate P. aeruginosa-induced PMN recruitment via production of IL-1alpha and beta. These findings have important implications for diseases involving P. aeruginosa infection and suggest novel targets for modulating P. aeruginosa-induced inflammation.

Protein phosphatase 2A and protein kinase Calpha are physically associated and are involved in Pseudomonas aeruginosa-induced interleukin 6 production by mast cells

Pulmonary infection with Pseudomonas aeruginosa is characterized by massive airway inflammation, which comprises significant cytokine production. Although mast cells are abundant in the lung and are potent sources of various cytokines, a role of mast cells in P. aeruginosa infection remains undefined, and P. aeruginosa-induced signaling mechanisms in mast cells have not been studied previously. Here we demonstrate that human cord blood-derived mast cells, mouse bone marrow-derived mast cells, and the mouse mast cell line MC/9 produce significant amounts of interleukin 6 (IL-6) in response to P. aeruginosa. This response was accompanied by a stimulation of protein kinase Calpha (PKCalpha) phosphorylation and PKC activity and was significantly blocked by the PKC inhibitors Ro 31-8220 and PKCalpha pseudosubstrate. Interestingly, mast cells treated with P. aeruginosa had reduced protein levels of phosphatase 2A catalytic unit (PP2Ac), which prompted us to determine whether a direct association between PKCalpha and PP2A occurs in mast cells. In mouse bone marrow-derived mast cells and MC/9 cells, as well as in the human mast cell line HMC-1, PP2A coimmunoprecipitated with PKCalpha either using PKCalpha- or PP2Ac-specific antibodies, suggesting that PKCalpha and PP2Ac are physically associated in mast cells. The PP2A inhibitor okadaic acid induced P. aeruginosa-like responses in mast cells including increased PKCalpha phosphorylation, stimulated PKC activity, and augmented IL-6 production, the last being blocked by the PKC inhibitor Ro 31-8220. Finally, okadaic acid potentiated the P. aeruginosa-induced IL-6 production. Collectively, these data provide, to our knowledge, the first evidence of both a direct physical association of PP2A and PKCalpha in mammalian cells and their coinvolvement in regulating mast cell activation in response to P. aeruginosa.

Periplasm, periplasmic spaces, and their relation to bacterial wall structure: novel secretion of selected periplasmic proteins from Pseudomonas aeruginosa

A brief overview of thin sections of cryopreserved walls from select eubacteria will be presented to suggest that all bacteria have functional periplasms, but that these are not necessarily confined to a periplasmic space such as found in typical gram-negative bacteria. Pseudomonas aeruginosa contains many components in its periplasmic space, some of which are required for infection. Throughout its growth cycle, P. aeruginosa blebs-off membrane vesicles that can possess DNA, endotoxin, phospholipase, protease, hemolysin, alkaline phosphatase, and autolysin, each of which must have a molecular phase that resides in the periplasm. These membrane packets make good delivery systems to convey these components to other bacteria and, possibly, tissue. Aminoglycoside antibiotics, such as gentamicin, produce a serious perturbation on the bacterium's surface (separate from the ribosomal effect), which contributes to the killing of the microorganism. Antibiotics such as this increase the size and number of the membrane blebs, which could contribute to septic shock of patients under drug therapy.

Bacterial phospholipases and pathogenesis

Phospholipases are produced from a diverse group of bacterial pathogens causing very different diseases. In some cases, secreted phospholipases appear to be the major cause of pathophysiological effects. Yet in other cases, phospholipases are key virulence factors, contributing to bacterial survival or dissemination without causing tissue destruction. Perhaps the most intriguing aspect of phospholipases as virulence factors is their potential to interfere with cellular signaling cascades and to modulate the host immune response.

Inability of histamine to regulate TNF-alpha production by human alveolar macrophages

Tumor necrosis factor alpha (TNF-alpha), a major product of alveolar macrophages (AM), has been implicated in many pulmonary diseases. Histamine, a mediator important in pulmonary inflammation, has been demonstrated to regulate the production of TNF-alpha by monocytes. In this study, we show that human AM and monocytes differ in their responses to histamine. Whereas histamine suppressed lipopolysaccharide (LPS)-stimulated TNF-alpha production by monocytes through a cAMP-dependent mechanism, it had no effect on either cAMP levels or TNF-alpha production by AM. In contrast, both PGE2 and IL-10 suppressed LPS-stimulated TNF-alpha production by AM and monocytes. The lack of response of AM to histamine appears unique, as histamine suppressed LPS-stimulated TNF-alpha production by mononuclear cells isolated from sites of acute and chronic inflammation, as well as from noninflammatory tissues, and by macrophages differentiated in vitro. In the presence of the phosphodiesterase (PDE) inhibitor 3-isobutyl-1-methylxanthine, histamine increased cAMP levels in AM. Freshly isolated monocytes and AM did not differ in PDE activity. However, PDE activity in AM, but not in monocytes, was increased 15 min after culture with histamine and may, in part, be responsible for the inability of histamine to suppress TNF-alpha production by AM. However, this increase was small and we hypothesize that additional mechanisms may contribute to the unresponsiveness of AM to histamine. We suggest that the lack of response of AM to histamine may be important in the host defense function of AM in the distal lung.

Role of Pseudomonas aeruginosa lipase in inflammatory mediator release from human inflammatory effector cells (platelets, granulocytes, and monocytes

Previously, we have shown that Pseudomonas aeruginosa lipase and phospholipase C (PLC), two extracellular lipolytic enzymes, interact with each other during 12-hydroxyeicosatetraenoic acid (HETE) generation from human platelets. In this regard. the addition of purified P. aeruginosa lipase to PLC-containing crude P. aeruginosa culture supernatants enhances the generation of the chemotactically active 12-HETE from human platelets. Therefore, we analyzed the interaction of purified P. aeruginosa lipase and purified hemolytic P. aeruginosa PLC with regard to inflammatory mediator release from human platelets, neutrophilic and basophilic granulocytes, and monocytes. Purified P. aeruginosa PLC, but not purified lipase by itself, induced 12-HETE generation from human platelets, the generation of leukotriene B4 (LTB4) and oxygen metabolites, enzyme release from human neutrophils, and histamine release from basophils but diminished interleukin-8 (IL-8) release from human monocytes in a dose-dependent manner. The addition of purified lipase enhanced PLC-induced 12-HETE and LTB4 generation, did not influence enzyme, histamine, or IL-8 release, but diminished the PLC-induced chemiluminescent response. Similar results were obtained when the hemolytic PLC from Clostridium perfringens was used instead of P. aeruginosa PLC. For further comparison, we used the well-defined calcium ionophore A23187 and phorbol-12-myristate-13-acetate (PMA) as stimuli. Lipase enhanced calcium ionophore-induced LTB4 generation and beta-glucuronidase release but reduced calcium ionophore-induced and PMA-induced chemiluminescence. In parallel, we analyzed the role of lipase in a crude P. aeruginosa culture supernatant containing PLC and lipase. Lipase activity in the P. aeruginosa culture supernatant was inhibited by treatment with the lipase-specific inhibitor hexadecylsulfonyl fluoride, leaving the activity of PLC unaffected. The capacity of "lipase-inactivated culture supernatant" to induce 12-HETE and LTB4 generation was diminished by 50 to 100%. Our results suggest that the simultaneous secretion of lipase and PLC by P. aeruginosa residing in an infected host may result in severe pathological effects which cannot be explained by the sole action of the individual virulence factor on inflammatory effector cells.

Eicosanoids, fatty acids and neutrophils: their relevance to the pathophysiology of disease

PUFA and their eicosanoid metabolites are potent biological modifiers. They have beneficial effects in a number of diseases, which may result in part from their direct actions on neutrophils as well as from their ability to modulate eicosanoid biosynthesis. A consideration of their interactions with other cell types, e.g. lymphocytes and macrophages, is beyond the scope of this review. Small alterations in structure can result in large changes in the neutrophil response. This will have important implications for the further development and use of fatty acids for therapeutic purposes.

Virulence factors are released from Pseudomonas aeruginosa in association with membrane vesicles during normal growth and exposure to gentamicin: a novel mechanism of enzyme secretion

Pseudomonas aeruginosa blebs-off membrane vesicles (MVs) into culture medium during normal growth. Release of these vesicles increased approximately threefold after exposure of the organism to four times the MIC of gentamicin. Natural and gentamicin-induced membrane vesicles (n-MVs and g-MVs and g-MVs, respectively) were isolated by filtration and differential centrifugation, and several of their biological activities were characterized. Electron microscopy of both n-MVs and g-MVs revealed that they were spherical bilayer MVs with a diameter of 50 to 150 nm. Immunoelectron microscopy and Western blot (immunoblot) analysis of the vesicles demonstrated the presence of B-band lipopolysaccharide (LPS), with a slightly higher proportion of B-band LPS in g-MVs than in n-MVs. A-band LPS was occasionally detected in g-MVs but not in n-MVs. In addition to LPS, several enzymes, such as phospholipase C, protease, hemolysin, and alkaline phosphatase, which are known to contribute to the pathogenicity of Pseudomonas infections were found to be present in both vesicle types. Both types of vesicles contained DNA, with a significantly higher content in g-MVs. These vesicles could thus play an important role in genetic transformation and disease by serving as a transport vehicle for DNA and virulence factors and are presumably involved in septic shock.

Eicosapentaenoic acid modulates neutrophil leukotriene B4 receptor expression in cystic fibrosis

In patients with cystic fibrosis (CF), high intrapulmonary concentrations of the neutrophil chemotaxin leukotriene B4 (LTB4) are associated with specific reduction of LTB4-induced chemotaxis of circulating neutrophils. The chemotactic abnormality is partially corrected by dietary supplementation with eicosapentaenoic acid (EPA). LTB4-induced neutrophil chemotaxis is mediated by specific, high-affinity, cell surface LTB4 receptors. The hypotheses that neutrophil LTB4 receptors are down-regulated in CF, and that EPA normalizes receptor expression, were tested by measuring the number (Rmax) and affinity (Kd) of LTB4 receptors on neutrophils from eight CF patients before and after EPA (6 weeks of 2.7 g/day), and from nine normal individuals. High-affinity receptor Rmax was depressed in CF patients (0.6 +/- 0.2 x 10(4)/cell (mean +/- s.d.) versus 1.8 +/- 0.7 x 10(4)/cell in normals), but corrected to normal (2.0 +/- 1.9 x 10(4)/cell) after EPA. High-affinity receptor Kd was depressed in CF patients (0.4 +/- 0.3 nM versus 1.4 +/- 0.5 nM in normals), and also corrected to normal with EPA (1.4 +/- 1.2 nM). Low-affinity receptors were depressed, but did not change significantly with EPA. These results indicate that neutrophil responses in chronic inflammatory lung disease can be influenced directly by LTB4 receptor modulation, and that this effect of EPA predominates over alterations in neutrophil signal transduction in situations of chronic exposure to LTB4.

Characteristics of Pseudomonas aeruginosa strains isolated from urinary tract infections

Thirty-three uropathogenic strains of Pseudomonas aeruginosa were investigated for hemolytic activity in both bacterial broth culture filtrates and isolate lyzates, resistance to bactericidal activity of fresh human serum, resistance to six antibiotics and plasmid DNA profile. Twenty-four of the 33 (73%) bacterial filtrates showed lysis of rabbit erythrocytes, as did the three after guinea-pig erythrocyte treatment. Twelve of 33 isolate lysates showed in parallel lysis of both types of erythrocytes used. Serum resistance was found in 17 (52%) isolates, intermediate resistance in 15 (45 %) isolates and only one isolate showed serum sensitivity. Resistance to antibiotics was detected as follows (in %): tetracycline 94, kanamycin 79, chloramphenicol 76, septrin 73, ampicillin 64, streptomycin 45, gentamicin 18. None of the isolates investigated showed resistance to colistine. With the exception of one isolate, plasmid DNA was detected in all P. aeruginosa strains.

Eicosapentaenoic acid in cystic fibrosis: evidence of a pathogenetic role for leukotriene B4

Much of the lung damage that limits the life of young adults with cystic fibrosis is due to proteases and oxygen metabolites generated by neutrophils, which are recruited into the airway by the interaction between Pseudomonas aeruginosa and pulmonary macrophages. Leukotriene B4 (LTB4) has been proposed as a local mediator of this process; its production is susceptible to specific modulation with dietary eicosapentaenoic acid (EPA). We carried out a placebo-controlled trial of EPA (2.7 g daily for 6 weeks) to assess its effects on markers of clinical state, peripheral neutrophil function, and lung inflammation in sixteen patients with cystic fibrosis colonised with P aeruginosa. EPA was well tolerated and resulted in a significant reduction in sputum volume (median change with EPA -10 mL/day, placebo 0; p = 0.015), and improvements in Schwachman score (EPA 5%, placebo 0; p = 0.034), forced expiratory volume in 1 s (EPA 0.25 L, placebo -0.1 L; p = 0.006), and vital capacity (EPA 0.6 L, placebo 0; p = 0.011). Relative chemotaxis of circulating neutrophils to LTB4 increased from a subnormal baseline of 4 (median; range 0-10) microns/30 min before treatment, to a near normal value of 11 (5-18) microns/30 min after EPA. Relative chemotaxis to LTB4 of patients taking placebo did not change: the difference in response was highly significant (p = 0.001). Specific reduction of neutrophil chemotaxis to LTB4 is a sensitive assay of chronic in-vivo exposure to LTB4. Our results suggest that LTB4 has a pathogenetic role in the lung damage of cystic fibrosis. Longer-term clinical trials of EPA are warranted in a larger number of cystic fibrosis patients.

Modulation of leukotriene generation by invasive bacteria

The effect of invasive bacteria on the release of proinflammatory mediators (oxygen radicals, leukotriene release) from human polymorphonuclear neutrophils was studied. Bacterial stimuli were used including genetically cloned invasive Yersinia enterocolitica strains 108-P (bearing the phagocytosis-resistance plasmid) and 108-C (plasmidless variant), Listeria monocytogenes [SLCC 5779 (inv-) and NCTC 7973 (inv+)] as well as an Escherichia coli K 12 strain (pRI 203) in which the inv gene of Y. pseudotuberculosis was cloned. When human polymorphonuclear granulocytes were studied as target cells the inv+ as well as the inv- strains were phagocytosed to a comparable amount with the exception of the L. monocytogenes strain (inv+). Among the invasive strains E. coli HB 101 (pRI 203) was the most active to trigger polymorphonuclear leucocytes (PMN) for oxygen radical production. Preincubation of the cells with bacteria and subsequent stimulation with the Ca ionophore A23187 or opsonized zymosan suppressed the chemiluminescence response to a different degree. The various bacterial strains did not induce leukotriene release from endogenous arachidonic acid. Subsequent stimulation of the infected cells with Ca ionophore or opsonized zymosan led to an altered pattern of the combined amounts of leukotriene B4 (LTB4), 20-OH- and 20-COOH-LTB4 as well as the ratio of LTB4 versus 20-OH and 20-COOH-LTB4. Infection of the cells also reduced strain dependently the number of LTB4-receptor sites. Our data suggest that bacterial uptake modulates the inflammatory response of granulocytes (e.g. chemiluminescence response, leukotriene generation).

Decreased polymorphonuclear leucocyte chemotactic response to leukotriene B4 in cystic fibrosis

Evidence that leukotriene B4 (LTB4) is a significant inflammatory mediator in chronic pseudomonal respiratory disease was sought in adolescents and young adults with cystic fibrosis. Specific chemotaxis of peripheral blood polymorphonuclear leucocytes (PMN) was used as an indirect measure of remote in vivo exposure to LTB4. PMN from 17 patients showed a significant decrease in chemotaxis to 10(-7)-10(-9) M LTB4, but normal responses to 10(-8) M n-formyl-methionyl-leucyl-phenylalanine and 4 mg/ml casein, when compared with 17 healthy age- and sex-matched controls. This result is consistent with chronic production of LTB4, and specific deactivation of circulating PMN receptors for LTB4 in patients with cystic fibrosis. Pharmacologic inhibition of LTB4 production in vivo may help elucidate its role in the pathogenesis of lung damage in cystic fibrosis.

Induction of inflammatory mediator release (serotonin and 12-hydroxyeicosatetraenoic acid) from human platelets by Pseudomonas aeruginosa glycolipid

Purified glycolipid from Pseudomonas aeruginosa induced the generation of significant amounts of 12-hydroxyeicosatetraenoic acid (12-HETE) and serotonin release from human platelets. The release of serotonin was first observed 2 min after addition of the glycolipid and increased with time. Significant serotonin release was obtained at glycolipid concentrations above 5 micrograms/ml and increased dose-dependently up to 100% at glycolipid concentrations above 40 micrograms/ml. Glycolipid induced 12-HETE in a time- and dose-dependent manner. 12-HETE formation was first measured after 10 min of incubation and increased with time. Optimal 12-HETE formation was obtained at a glycolipid concentration of 50 micrograms/ml; higher concentrations of glycolipid led to a decrease in 12-HETE formation, indicating a cytotoxic effect. Stimulation of platelets with glycolipid (12-HETE formation and serotonin release) was accompanied by calcium influx, translocation of protein kinase C, activation of guanylylimidodiphosphate binding, and increased GTPase activity in platelet membranes within the same concentration range.

Effects of mucoid and non-mucoid Pseudomonas aeruginosa isolates from cystic fibrosis patients on inflammatory mediator release from human polymorphonuclear granulocytes and rat mast cells

Mucoid Pseudomonas aeruginosa causing chronic bronchopulmonary infection in cystic fibrosis (CF) patients may interfere with host defence mechanisms. We investigated 13 P. aeruginosa strains isolated from sputa of CF patients with regard to the induction or modulation of inflammatory mediator release from human neutrophils (PMN) and rat mast cells. The effects of mucoid as compared to non-mucoid bacteria were studied using a mucoid strain and its non-mucoid revertant. The release of leukotrienes (LT) and histamine in response to the majority of the CF strains was insignificant. However, preincubation of PMN with P. aeruginosa caused a dose-dependent decrease (50-95%) of LTB4 and LTC4 generation and LTB4 metabolism induced by the Ca(2+)-ionophore A23187 or opsonized zymosan (ZX) (P less than 0.001). The mucoid strains caused a three- to 10-fold higher impairment of LTB4 release (P less than 0.05) and a concomitant down-regulation of LTB4 receptors on neutrophils. Inhibitory effects were also obtained for mucoid and non-mucoid bacteria when the phorbol-ester or the Ca(2+)-ionophore induced luminol enhanced chemiluminescence response (P less than 0.001) or the histamine release from rat peritoneal mast cells (P less than 0.01) was studied. The bacteria-cell contact with non-mucoid strains was associated with an increased Ca2+ influx into PMN, whereas mucoid bacteria had no effect. In addition, a protein kinase C-dependent decrease of the C3bi receptor was suppressed by the mucoid--and less effectively--by the non-mucoid strain. The results suggest that the impairment of the phagocytic and inflammatory system may contribute to the pathogenesis and persistence of mucoid P. aeruginosa infection in CF.

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.

Arachidonic acid metabolites in middle ear effusions of children

Middle ear effusions (MEEs) from 78 children (98 ears) with otitis media were examined for products of arachidonic acid (AA) metabolism, including leukotrienes B4, C4, D4, and E4 and prostaglandins D2 and E2, by high-performance liquid chromatography. Leukotrienes B4 and D4 were recovered most frequently: 59% and 54%, respectively. Leukotriene B4 was found in highest concentration, 1.29 +/- 3.46 ng/0.1 mL. The concentrations of leukotrienes B4 (p less than .03), (4 (p less than .01), and E4 (p less than .02) were significantly higher in culture-positive than in culture-negative MEEs. Neither the concentration nor the type of AA metabolite correlated with bacterial species isolated, chronicity of effusion, age of subject, or consistency of MEE. These data suggest that the AA metabolites are synthesized relatively frequently during otitis media of childhood. Leukotriene B4 is the most frequently detected AA metabolite in MEEs and is highly associated with the presence of viable bacteria.

Elevated urinary leukotriene E4 excretion in patients with ARDS and severe burns

Increased synthesis of peptidoleukotrienes may occur in a variety of inflammatory diseases. To test this theory, hospitalized patients with a variety of diseases were studied and urine LTE4 quantitated as an index of total body peptidoleukotriene synthesis. 10 patients with ARDS, 7 of which had additional organ involvement, and 5 patients suffering from severe burn injuries were studied. Patients with uncomplicated ARDS excreted approximately 6-fold higher amounts of LTE4 in urine compared to healthy subjects. When ARDS was complicated by multiple organ failure (MOF), urine LTE4 levels were 2- to 150-fold higher than in healthy volunteers. Patients with severe burn injuries had peak urine LTE4 levels which were approximately 20-fold higher than in healthy volunteers. As additional controls, patients with cardiac arrhythmias (absence of inflammatory disease) and patients with uncomplicated pneumonia (localized inflammation) showed normal or mildly elevated urinary LTE4 levels. The urinary LTE4 levels in ARDS patients did not correlate with serum creatinine, bilirubin, or LDH levels, or with the WBC, nor did renal or liver failure by itself predict extremely elevated urinary LTE4 levels. In conclusion, patients with ARDS or ARDS/MOF and patients with severe injuries and sepsis syndrome excrete higher levels of urinary LTE4 than patients healthy volunteers or patients with limited inflammatory disease. In certain situations, urinary LTE4 levels may be useful as a marker of the degree of inflammation.

Characterization of phospholipase C from Pseudomonas aeruginosa as a potent inflammatory agent

Phospholipase C (PLC) from Pseudomonas aeruginosa induced a marked inflammatory response when injected intraperitoneally in C3H/HeJ mice. This inflammation was characterized by the accumulation of inflammatory cells and plasma protein and the release of arachidonic acid metabolites (6-trans-12-epi-leukotriene B4 [LTB4], 6-trans-LTB4, LTB4, 5-HETE (5-hydroxyeicosatetraenoic acid), LTC4, LTD4, LTE4, prostaglandin E2 [PGE2], PGF2-alpha, and thromboxane B2 [TxB2]) in the peritoneal cavity of the mice. Heat-inactivated PLC did not evoke any of these effects, suggesting that enzyme activity is necessary for PLC-induced inflammation. When human granulocytes were incubated with PLC in vitro, 6-trans-12-epi-LTB4, 6-trans-LTB4, LTB4, 5-HETE, and PGE2 were generated. Mouse peritoneal cells stimulated with PLC released 6-trans-LTB4, LTB4, PGE2, PGF2-alpha, and TxB2. Both human granulocytes and mouse peritoneal cells stimulated with PLC generated significantly increased levels of arachidonic acid metabolites as compared with cells incubated with heat-inactivated PLC. Leukotriene production by both populations of cells was inhibited when the cells were preincubated with nordihydroguaiaretic acid and subsequently stimulated with PLC. Similarly, both cell types released significantly lower amounts of cyclooxygenase pathway products when they were preincubated with indomethacin and subsequently stimulated with PLC.