Macrolide antibiotics inhibit nitric oxide generation by rat pulmonary alveolar macrophages

Azithromycin Exerts Bactericidal Activity and Enhances Innate Immune Mediated Killing of MDR Achromobacter xylosoxidans

Azithromycin (AZM), the most commonly prescribed antibiotic in the United States, is thought to have no activity against multidrug-resistant Gram-negative pathogens such as Achromobacter xylosoxidans (AX) per standard minimum inhibitory concentration testing in cation-adjusted Mueller Hinton Broth. Here we provide the first report of AZM bactericidal activity against carbapenem-resistant isolates of AX, with a multifold decrease in minimum inhibitory concentration across 12 clinical isolates when examined under physiologic testing conditions that better recapitulate the in vivo human environment. This pharmaceutical activity, evident in eukaryotic tissue culture media, is associated with enhanced AZM intracellular penetration and synergistic killing with human whole blood, serum, and neutrophils. Additionally, AZM monotherapy inhibited preformed AX biofilm growth in a dose-dependent manner together with a reduction in viable bacteria. In an illustrative case, AZM in combination with piperacillin-tazobactam exerted clear therapeutic effects in a patient with carbapenem-resistant AX mediastinitis, sternal osteomyelitis, and aortic graft infection. Our study reinforces how current antimicrobial testing practices fail to recapitulate the host environment or host-pathogen interactions and may misleadingly declare complete resistance to useful agents, adversely affecting patient outcomes. We conclude that AZM merits further exploration in the treatment of drug-resistant AX infections. Novel approaches to antimicrobial susceptibility testing that better recapitulate the host environment should be considered, especially as infections caused by multidrug-resistant Gram-negative bacterial pathogens are expanding globally with high morbidity and mortality.

Exploring the Role of CYP3A4 Mediated Drug Metabolism in the Pharmacological Modulation of Nitric Oxide Production

Nitric-oxide synthase, the enzyme responsible for mammalian nitric oxide generation, and cytochrome P450, the major enzymes involved in drug metabolism, share striking similarities. Therefore, it makes sense that cytochrome P450 drug mediated biotransformations might play an important role in the pharmacological modulation of nitric oxide synthase. In this work, we have undertaken an integrated in vitro assessment of the hepatic metabolism and nitric oxide modulation of previously described dual inhibitors (imidazoles and macrolides) of these enzymes in order assess the implication of CYP450 activities over production of nitric oxide. In vitro systems based in human liver microsomes and activated mouse macrophages were developed for these purposes. Additionally in vitro production the hepatic metabolites of dual inhibitor, roxithromycin, was investigated achieving the identification and isolation of main hepatic biotransformation products. Our results suggested that for some macrolide compounds, the cytochrome P450 3A4 derived drug metabolites have an important effect on nitric oxide production and might critically contribute to the pharmacological immunomodulatory activity observed.

An Interactive Macrophage Signal Transduction Map Facilitates Comparative Analyses of High-Throughput Data

Macrophages (Mϕs) are key players in the coordination of the lifesaving or detrimental immune response against infections. The mechanistic understanding of the functional modulation of Mϕs by pathogens and pharmaceutical interventions at the signal transduction level is still far from complete. The complexity of pathways and their cross-talk benefits from holistic computational approaches. In the present study, we reconstructed a comprehensive, validated, and annotated map of signal transduction pathways in inflammatory Mϕs based on the current literature. In a second step, we selectively expanded this curated map with database knowledge. We provide both versions to the scientific community via a Web platform that is designed to facilitate exploration and analysis of high-throughput data. The platform comes preloaded with logarithmic fold changes from 44 data sets on Mϕ stimulation. We exploited three of these data sets-human primary Mϕs infected with the common lung pathogens Streptococcus pneumoniae, Legionella pneumophila, or Mycobacterium tuberculosis-in a case study to show how our map can be customized with expression data to pinpoint regulated subnetworks and druggable molecules. From the three infection scenarios, we extracted a regulatory core of 41 factors, including TNF, CCL5, CXCL10, IL-18, and IL-12 p40, and identified 140 drugs targeting 16 of them. Our approach promotes a comprehensive systems biology strategy for the exploitation of high-throughput data in the context of Mϕ signal transduction. In conclusion, we provide a set of tools to help scientists unravel details of Mϕ signaling. The interactive version of our Mϕ signal transduction map is accessible online at https://vcells.net/macrophage.

Macrolide therapy in chronic inflammatory diseases

Macrolides are a group of antibiotics with a distinctive macrocyclic lactone ring combined with sugars (cladinose, desosamine). The action of macrolides is to block protein synthesis by binding to the subunit of 50S ribosome of bacteria. Prototype macrolide was erythromycin, which came into clinical practice in the 50s of the 20th century. Its antimicrobial spectrum covers the scope of the penicillins but is extended to the impact of atypical bacteria. In the 90s more drugs of this group were synthesized—they have less severe side effects than erythromycin, extended spectrum of Gram-negative bacteria. Macrolides are effective in treating mycobacterial infections especially in patients infected with HIV. It is now known that in addition to antibacterial abilities, macrolides have immunomodulatory effects—they inhibit the production of proinflammatory cytokines (TNF, IL1, 6, and 8) affect transcription factors (NF-κB) as well as costimulaton (CD 80) and adhesion molecules (ICAM). This review article focused not only on the their antimicrobial abilities but also on efficacy in the treatment of several inflammatory disorders independent of the infectious agent. Their wider use as immunomodulators requires further study, which can lead to an extension of indications for their administration.

Mechanisms of action and clinical application of macrolides as immunomodulatory medications

Macrolides have diverse biological activities and an ability to modulate inflammation and immunity in eukaryotes without affecting homeostatic immunity. These properties have led to their long-term use in treating neutrophil-dominated inflammation in diffuse panbronchiolitis, bronchiectasis, rhinosinusitis, and cystic fibrosis. These immunomodulatory activities appear to be polymodal, but evidence suggests that many of these effects are due to inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation and nuclear factor kappa B (NF-kappaB) activation. Macrolides accumulate within cells, suggesting that they may associate with receptors or carriers responsible for the regulation of cell cycle and immunity. A concern is that long-term use of macrolides increases the emergence of antimicrobial resistance. Nonantimicrobial macrolides are now in development as potential immunomodulatory therapies.

Macrolide antibiotics as immunomodulatory medications: proposed mechanisms of action

Macrolide antibiotics administered in sub-antimicrobial doses improve pulmonary function and decrease exacerbation frequency for persons with diffuse panbronchiolitis or cystic fibrosis. Data also suggest a beneficial effect of macrolide antibiotics in the treatment of steroid dependent asthma. Many potential immunomodulatory effects of macrolide antibiotics have been reported including the ability to down-regulate prolonged inflammation, decreasing airway mucus secretion, inhibiting bacterial biofilm, decreasing the production of reactive oxygen species, inhibiting neutrophil activation and mobilization, accelerating neutrophil apoptosis, and blocking the activation of nuclear transcription factors. Macrolides initially decrease, then increase, and have finally a sustained suppression of cytokine secretions from normal human bronchial epithelial cells through inhibition and activation of extracellular signal-regulated kinases (ERK) and then reversibly retard cell proliferation probably through ERK. Consistent with this, macrolide antibiotics possibly reduce mucin production as well as neutrophil migration by interfering with ERK signal transduction.

Inhibition of sulfur mustard-induced cytotoxicity and inflammation by the macrolide antibiotic roxithromycin in human respiratory epithelial cells

BACKGROUND

Sulfur mustard (SM) is a potent chemical vesicant warfare agent that remains a significant military and civilian threat. Inhalation of SM gas causes airway inflammation and injury. In recent years, there has been increasing evidence of the effectiveness of macrolide antibiotics in treating chronic airway inflammatory diseases. In this study, the anti-cytotoxic and anti-inflammatory effects of a representative macrolide antibiotic, roxithromycin, were tested in vitro using SM-exposed normal human small airway epithelial (SAE) cells and bronchial/tracheal epithelial (BTE) cells. Cell viability, expression of proinflammatory cytokines including interleukin (IL)-1beta, IL-6, IL-8 and tumor necrosis factor (TNF), and expression of inducible nitric oxide synthase (iNOS) were examined, since these proinflammatory cytokines/mediators are import indicators of tissue inflammatory responses. We suggest that the influence of roxithromycin on SM-induced inflammatory reaction could play an important therapeutic role in the cytotoxicity exerted by this toxicant.

RESULTS

MTS assay and Calcein AM/ethidium homodimer (EthD-1) fluorescence staining showed that roxithromycin decreased SM cytotoxicity in both SAE and BTE cells. Also, roxithromycin inhibited the SM-stimulated overproduction of the proinflammatory cytokines IL-1beta, IL-6, IL-8 and TNF at both the protein level and the mRNA level, as measured by either enzyme-linked immunosorbent assay (ELISA) or real-time RT-PCR. In addition, roxithromycin inhibited the SM-induced overexpression of iNOS, as revealed by immunocytochemical analysis using quantum dots as the fluorophore.

CONCLUSION

The present study demonstrates that roxithromycin has inhibitory effects on the cytotoxicity and inflammation provoked by SM in human respiratory epithelial cells. The decreased cytotoxicity in roxithromycin-treated cells likely depends on the ability of the macrolide to down-regulate the production of proinflammatory cytokines and/or mediators. The results obtained in this study suggest that macrolide antibiotics may serve as potential vesicant respiratory therapeutics through mechanisms independent of their antibacterial activity.

Effects of a short-course of amoxicillin/clavulanic acid on systemic and mucosal immunity in healthy adult humans

Although amoxicillin/clavulanic acid (AMC) is the most frequently administered antibiotic in France, its in vivo effects on immunity in healthy adults have never, to our knowledge, been described. Eighteen healthy adult male volunteers, 25+/-6 years old, were treated for 5 days with oral amoxicillin (1 g) /clavulanate potassium (125 mg), two times daily. Systemic and local intestinal immunity parameters were sequentially explored before, during and after the antibiotic treatment. No significant differences were obtained for transudation markers (albumin and alpha1-antitrypsin) in sera, feces and saliva, showing that AMC did not induce inflammatory reaction. Phagocytosis, peripheral blood cell subsets, intracellular interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha production by natural killer (NK) cells and cytotoxic T lymphocytes, intracellular TNF-alpha production by monocytes showed no significant differences throughout the trial. In fecal outputs, no significant differences were found in secretory immunoglobulin A (S-IgA), lactoferrin (Lf), lysozyme (Lz) and transforming growth factor (TGF)-beta1. In sera, concentrations of total IgA (T-IgA), S-IgA, IgM, Lf and Lz did not show any significant variations throughout the study, whereas concentrations of IgG were slightly but significantly reduced 15 days after AMC treatment. In saliva, concentrations of T-IgA were slightly but significantly higher, whereas S-IgA concentrations were unchanged. Our results showed that oral AMC intake did not induce any significant adverse effects on immunity in adult humans.

New perspectives on macrolide antibiotics

Macrolides are not used exclusively for the treatment of community-acquired respiratory tract infections. Their ability to penetrate cells makes them highly suitable for the treatment of diseases caused by intracellular pathogens, such as non-gonococcal urethritis and trachoma. Azithromycin is approved for these indications. Clinical studies have also been conducted, or are currently being carried out, to assess the use of macrolides in the treatment of atherosclerosis, eradication of Helicobacter pylori and the management of life-threatening gastrointestinal diseases, cystic fibrosis and malaria.

Inhibition of nuclear pre-mRNA splicing by antibiotics in vitro

A number of antibiotics have been reported to disturb the decoding process in prokaryotic translation and to inhibit the function of various natural ribozymes. We investigated the effect of several antibiotics on in vitro splicing of a eukaryotic nuclear pre-mRNA (beta-globin). Of the eight antibiotics studied, erythromycin, Cl-tetracycline and streptomycin were identified as splicing inhibitors in nuclear HeLa cell extract. The K(i) values were 160, 180 and 230 microm, respectively. Cl-tetracycline-mediated and streptomycin-mediated splicing inhibition were in the molar inhibition range for hammerhead and human hepatitis delta virus ribozyme self-cleavage (tetracycline), of group-I intron self-splicing (streptomycin) and inhibition of RNase P cleavage by some aminoglycosides. Cl-tetracycline and the aminocyclitol glycoside streptomycin were found to have an indirect effect on splicing by unspecific binding to the pre-mRNA, suggesting that the inhibition is the result of disturbance of the correct folding of the pre-mRNA into the splicing-compatible tertiary structure by the charged groups of these antibiotics. The macrolide, erythromycin, the strongest inhibitor, had only a slight effect on formation of the presplicing complexes A and B, but almost completely inhibited formation of the splicing-active C complex by binding to nuclear extract component(s). This results in direct inhibition of the second step of pre-mRNA splicing. To our knowledge, this is the first report on specific inhibition of nuclear splicing by an antibiotic. The functional groups involved in the interaction of erythromycin with snRNAs and/or splicing factors require further investigation.

Macrolide antibiotics and pulmonary inflammation

Many clinically effective therapeutic agents can exhibit localized and systemic effects that are manifestly different from their intended primary pharmacological mode of action. Macrolide antibiotics such as erythromycin and its derivatives are no exception. In addition to their antibacterial action, this class of antibiotics exhibits anti-inflammatory activity in a variety of airway diseases such as asthma and diffuse panbronchiolitis that is separate and distinct from a direct antibacterial action. A variety of erythromycin derivatives have been shown to be clinically beneficial in these airway diseases. The anti-inflammatory activities of these macrolide antibiotics are becoming a research topic of intense interest. Recent work in this field has led to the understanding of the various physiological, cellular and molecular processes of the inflammatory response that are inhibited or suppressed by these compounds. This review presents a brief summary of the fascinating recent work in this active research area.

Anti-inflammatory effects of macrolide antibiotics

Macrolides are widely used as antibacterial drugs. Clinical and experimental data, however, indicate that they also modulate inflammatory responses, both contributing to the treatment of infective diseases and opening new opportunities for the therapy of other inflammatory conditions. Considerable evidence, mainly from in vitro studies, suggests that leukocytes and neutrophils in particular, are important targets for modulatory effects of macrolides on host defense responses. This underlies the use of the 14-membered macrolide erythromycin for the therapy of diffuse panbronchiolitis. A variety of other inflammatory mediators and processes are also modulated by macrolides, suggesting that the therapeutic indications for these drugs may be extended significantly in future.

Evaluation of blood vessels and edema in the airways of asthma patients: regulation with clarithromycin treatment

BACKGROUND

Although airway angiogenesis and edema have been proposed to contribute to the airway remodeling process in patients with asthma, there are few studies looking at these structural components in the airway tissue of asthma patients. Mycoplasma infection may be associated with chronic asthma and has been shown to induce angiogenesis and edema in a murine model.

PARTICIPANTS AND MEASUREMENTS

We evaluated blood vessels and edema by immunohistochemistry in endobronchial biopsy samples from 10 normal control subjects and 15 patients with mild-to-moderate asthma before and after a 6-week treatment with clarithromycin (n = 8) or placebo (n = 7). Type IV collagen and alpha(2)-macroglobulin were used to identify blood vessels and edema in the tissue, respectively. Mycoplasma pneumoniae was evaluated by polymerase chain reaction.

SETTING

National Jewish Medical and Research Center.

RESULTS

At baseline, the vascularity, the number of blood vessels, and the edematous area in the airway tissue were not significantly different between asthmatic patients and normal control subjects. However, asthmatic patients demonstrated increased blood vessel size compared with normal control subjects (p = 0.03). After clarithromycin treatment in asthmatic patients, the number of blood vessels was increased (p = 0.02), while edema decreased (p = 0.049). Asthmatic patients who tested positive for M pneumoniae showed a significant increase in vascularity than asthmatic patients who tested negative for M pneumoniae (p = 0.02).

CONCLUSION

Our data suggest that angiogenesis and edema may not be significant features of airway remodeling in patients with chronic, mild-to-moderate asthma. Clarithromycin treatment in asthmatic patients could reduce the edematous area as identified by alpha(2)-macroglobulin staining, which may lead to airway tissue shrinkage and cause an artificial increase in the number of blood vessels.