Diffuse Panbronchiolitis

Quorum-sensing antagonistic activities of azithromycin in Pseudomonas aeruginosa PAO1: a global approach

The administration of macrolides such as azithromycin for chronic pulmonary infection of cystic fibrosis patients has been reported to be of benefit. Although the mechanisms of action remain obscure, anti-inflammatory effects as well as interference of the macrolide with Pseudomonas aeruginosa virulence factor production have been suggested to contribute to an improved clinical outcome. In this study we used a systematic approach and analyzed the impact of azithromycin on the global transcriptional pattern and the protein expression profile of P. aeruginosa PAO1 cultures versus those in untreated controls. The most remarkable result of this study is the finding that azithromycin exhibited extensive quorum-sensing antagonistic activities. In accordance with the inhibition of the quorum-sensing systems, virulence factor production was diminished and the oxidative stress response was impaired, whereas the type III secretion system was strongly induced. Moreover, P. aeruginosa motility was reduced, which probably accounts for the previously observed impaired biofilm formation capabilities of azithromycin-treated cultures. The interference of azithromycin with quorum-sensing-dependent virulence factor production, biofilm formation, and oxidative stress resistance in P. aeruginosa holds great promise for macrolide therapy in cystic fibrosis. Clearly quorum-sensing antagonist macrolides should be paid more attention in the management of chronic P. aeruginosa infections, and as quorum-sensing antagonists, macrolides might gain vital importance for more general application against chronic infections.

Chlamydophila pneumoniae and Mycoplasma pneumoniae: a role in asthma pathogenesis?

The potential role of atypical bacterial infection in the pathogenesis of asthma is a subject of continuing debate. There is an increasing body of literature concerning the association between the atypical bacteria Chlamydophila pneumoniae and Mycoplasma pneumoniae and asthma pathogenesis; however, many studies investigating such a link have been uncontrolled and have provided conflicting evidence, in part due to the difficulty in accurately diagnosing infection with these atypical pathogens. This article reviews the evidence for an association between atypical bacterial respiratory pathogens and the pathogenesis of asthma, and discusses the biological mechanisms that could account for such a link. The possible role of antibacterial therapy in the management of asthma and the need for well-designed studies to investigate this is also discussed.

Clinical and immunological aspects of HLA class I deficiency

Human leukocyte antigen (HLA) class I deficiency is a rare disease with remarkable clinical and biological heterogeneity. The spectrum of possible manifestations extends from the complete absence of symptoms to life-threatening disease conditions. It is usually diagnosed when HLA class I serological typing is unsuccessful; flow cytometric studies then reveal a severe reduction in the cell surface expression of HLA class I molecules (90-99% reduction compared to normal cells). In most cases to date, this low expression is due to a homozygous inactivating mutation in one of the two subunits of the transporter associated with antigen processing (TAP), critically involved in the peptide loading of HLA class I molecules. Although asymptomatic cases have been described, TAP deficiencies are usually characterized by chronic bacterial infections of the upper and lower airways, evolving to bronchiectasis, and in half of the cases, also skin ulcers with features of a chronic granulomatous inflammation. Despite the defect in HLA class-I-mediated presentation of viral antigens to cytotoxic T cells, the patients do not suffer from severe viral infections, presumably because of other efficient antiviral defence mechanisms such as antibodies, non-HLA-class-I-restricted cytotoxic effector cells and CD8+ T-cell responses to TAP-independent antigens. Treatment is at present exclusively symptomatic, and should particularly focus on the prevention of bronchiectasis, which requires early detection.

Modulation of neutrophil and inflammation markers in chronic obstructive pulmonary disease by short-term azithromycin treatment

The anti-inflammatory potential of azithromycin in chronic obstructive pulmonary disease (COPD) patients was explored following a standard oral dosing regimen. Patients with moderate and severe COPD were treated with azithromycin (500 mg, n=16) or placebo (n=8) once daily for 3 days in a randomized, double blind design, to compare effects on inflammation markers with those seen in a previous study in healthy volunteers. A battery of tests was made on serum, blood neutrophils and sputum on days 1 (baseline), 3, 4, 11, 18 and 32. In comparison to placebo, azithromycin resulted in an early transient increase in serum nitrites plus nitrates (day 3), associated with a tendency towards an increase in the blood neutrophil oxidative burst to phorbol myristic acetate. Subsequently, prolonged decreases in blood leukocyte and platelet counts, serum acute phase protein (including C reactive protein) and soluble E-selectin and blood neutrophil lactoferrin concentrations and a transient decrease in serum interleukin-8 were observed. Blood neutrophil glutathione peroxidase activity showed a prolonged increase after azithromycin treatment. The biphasic facilitatory-then-inhibitory response to azithromycin seen in healthy volunteers is not so clearly detectable in COPD patients, only potential anti-inflammatory effects. Treatment for longer periods may give therapeutic anti-inflammatory benefit in these patients.

[Quorum sensing: the possibility of the new antibiotic target in bacterial infection]

Expression of many virulence factors in P. aeruginosa is regulated by a cell density dependent mechanism called quorum sensing. Quorum sensing allows P. aeruginosa to sense the density of the surrounding bacterial population and to coordinately regulate transcription of various virulence genes. Pseucomonas aeruginosa is a common pathogen infecting chronic respiratory infections, such as diffuse panbronchiolitis (DPB) patients. Although these patients are typically treated with multiple anti-pseudomonal antibiotics, the infection is rarely eradicated and often results in mortality. In the 1980s it was reported that long-term therapy with low doses of erythromycin improved the clinical symptoms of DPB patients colonized with P. qeruginosa. Recently it has been demonstrated that sub MIC concentrations of macrolides strongly inhibite Pseudomonas quorum sensing system. These data suggested a novel mechanism of quorum sensing regulation of antibiotic sensitivity.

Suppressive activity of macrolide antibiotics on nitric oxide production by lipopolysaccharide stimulation in mice

BACKGROUND: Low-dose and long-term administration of macrolide antibiotics into patients with chronic airway inflammatory diseases could favorably modify their clinical conditions. However, the therapeutic mode of action of macrolides is not well understood. Free oxygen radicals, including nitric oxide (NO), are well recognized as the important final effector molecules in the development and the maintenance of inflammatory diseases. PURPOSE: The influence of macrolide antibiotics on NO generation was examined in vivo. METHODS: Male ICR mice, 5 weeks of age, were orally administered with either roxithromycin, clarithromycin, azithromycin or josamycin once a day for 2-4 weeks. The mice were then injected intraperitoneally with 5.0 mg/kg lipopolysaccharide (LPS) and the plasma NO level was examined 6 h later. RESULTS: Although pre-treatment of mice with macrolide antibiotics for 2 weeks scarcely affected NO generation by LPS injection, the administration of macrolide antibiotics, except for josamycin, for 4 weeks significantly inhibited LPS-induced NO generation. The data in the present study also showed that pre-treatment of mice with macrolide antibiotics for 4 weeks significantly suppresses not only production of pro-inflammatory cytokines interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha, but also inducible nitric oxide synthase mRNA expressions, which are enhanced by LPS injection. CONCLUSION: These results strongly suggest that suppressive activity of macrolide antibiotics on NO generation in response to LPS stimulation in vivo may, in part, account for the clinical efficacy of macrolides on chronic inflammatory diseases.

Macrolides in cystic fibrosis: is there a role?

A spectrum of anti-inflammatory properties, evidence of anti-infective action against Pseudomonas aeruginosa at sub-inhibitory concentrations and positive clinical experience in patients with diffuse panbronchiolitis, a disease with features in common with cystic fibrosis (CF), has prompted research to evaluate the role of macrolide therapy in patients with CF. Newer macrolides such as azithromycin have the advantage of improved tolerability and a prolonged intracellular half-life requiring an infrequent dosing regimen. Results from initial studies suggest a benefit from several months of macrolide therapy in patients with CF. An improvement in lung function was initially shown in a small open study in children, while maintenance of lung function compared with placebo, reduced acute respiratory exacerbations, and reduced systemic markers of inflammation were demonstrated in a randomized, placebo-controlled study of macrolide therapy in adult patients with CF. Additional controlled studies are required to determine optimal drug, dosage, and duration of therapy, and long-term adverse effects of prolonged therapy with macrolides in patients with CF. The potential, with long-term use, to induce resistance against other bacteria colonizing the upper respiratory tract e.g. pneumococci has not been explored. Measurement of cytokines and inflammatory mediators from the sputum of patients with CF is technically difficult and does not correlate with disease activity. There is a need for easily measurable, reproducible and clinically meaningful end-points for evaluation of new therapies in CF. The choice of appropriate outcome measures, apart from lung function, to monitor disease activity needs careful consideration in clinical trials determining the efficacy of macrolides in patients with CF. Evidence-based recommendations for the use of macrolides in the treatment of CF are not expected for some years although macrolides are already being prescribed for long-term use in some centers. There is a need for further research into mechanisms of anti-inflammatory action of macrolides in the lungs of patients with CF and whether or not such therapy may be beneficial in the long term.

Suppressive activity of macrolide antibiotics on nitric oxide production from nasal polyp fibroblasts in vitro

The influence of macrolide antibiotics on nitric oxide (NO) generation was examined using human nasal polyp fibroblasts (NPFs) in vitro. Addition of roxithromycin (RXM) at a concentration of > 7.5 microg/ml to cell cultures was shown to suppress NO production in response to stimulation with 25.0 ng/ml tumor necrosis factor (TNF)-alpha. However, jyosamycin (JM) did not suppress NO production from NPFs induced by TNF-alpha stimulation in vitro, even when added to cell cultures at a concentration of 20.0 microg/ml. We then examined the influence of RXM on inducible nitric oxide synthase (iNOS) mRNA expression in NPFs. Addition of RXM at a dose of 7.5 microg/ml to cell cultures caused reduction of iNOS mRNA expression, which was enhanced by TNF-alpha stimulation in vitro.