Membrane-stabilizing, anti-inflammatory interactions of macrolides with human neutrophils

Effect of azithromycin treatment on endothelial function in patients with coronary artery disease and evidence of Chlamydia pneumoniae infection

BACKGROUND

It has been suggested that infection with Chlamydia pneumoniae(CPn) can trigger inflammatory mechanisms that may in turn impair vascular endothelial function. The aim of the present study was to assess whether treatment with the macrolide antibiotic azithromycin improves endothelial function in patients with coronary artery disease and antibodies positive to CPn.

METHODS AND RESULTS

We carried out a randomized, prospective, double-blind, placebo-controlled trial in 40 male patients (mean age, 55+/-9 years) with documented coronary artery disease and positive CPn-IgG antibody titers. After baseline evaluation, patients were randomized to receive either azithromycin or placebo for 5 weeks. Flow-mediated dilation (FMD) of the brachial artery and E-selectin, von Willebrand factor, and C-reactive protein (CRP) levels were assessed at study entry and at the end of the treatment period. Our results showed that patients who received azithromycin had a significant improvement in FMD (mean change, 2.1+/-1.1%; P<0.005). In contrast, FMD was not significantly changed in the placebo group (mean change, -0.02+/-0.2%, P=0.64). Azithromycin therapy also resulted in a significant decrease of E-selectin and von Willebrand factor levels. CRP levels were not significantly altered by treatment with either azithromycin or placebo. Beneficial effects of azithromycin treatment were independent from the presence of low (<1:32) or high (> or =1:32) CPn antibody titers.

CONCLUSIONS

Our findings indicate that treatment with azithromycin has a favorable effect on endothelial function in patients with documented coronary artery disease and evidence of CPn infection irrespective of antibody titer levels. Whether these favorable actions of antibiotic treatment will translate into a beneficial effect on atherogenesis and cardiac events needs further investigation.

Long-term clarithromycin decreases prednisone requirements in elderly patients with prednisone-dependent asthma

Prolonged use of prednisone is associated with serious side effects, such as osteoporosis, particularly among elderly individuals. Macrolide antibiotics exhibit anti-inflammatory effects that are distinct from their antimicrobial properties. Thus, the purpose of this case report is to describe the effects of prolonged treatment with clarithromycin, 500 mg bid, in reducing prednisone requirements in three elderly patients with prednisone-dependent asthma. Three patients (one woman and two men) aged 63 to 69 years, who had been treated with 5 to 10 mg prednisone daily for at least the last 12 months, were given clarithromycin, 500 mg bid. They were followed regularly for changes in daily prednisone dose, spirometry, quality of life, and adverse events. The prednisone dose was tapered in a stepwise fashion at each clinic visit. Within 3 to 6 months of initiation of treatment with clarithromycin, and throughout the 12-month follow-up, two of three patients discontinued prednisone therapy, while the third patient displayed increased spirometry readings and noted an increasingly better quality of life. Pulmonary function tests were stable or improved over this time period, with no reported adverse events, including increased rate of infections. One patient relapsed upon discontinuation of clarithromycin therapy but has since responded to re-initiation of treatment. Long-term oral clarithromycin may have a role in reducing prednisone requirements in elderly patients with prednisone-dependent asthma.

Interference of antibacterial agents with phagocyte functions: immunomodulation or "immuno-fairy tales"?

Professional phagocytes (polymorphonuclear neutrophils and monocytes/macrophages) are a main component of the immune system. These cells are involved in both host defenses and various pathological settings characterized by excessive inflammation. Accordingly, they are key targets for immunomodulatory drugs, among which antibacterial agents are promising candidates. The basic and historical concepts of immunomodulation will first be briefly reviewed. Phagocyte complexity will then be unravelled (at least in terms of what we know about the origin, subsets, ambivalent roles, functional capacities, and transductional pathways of this cell and how to explore them). The core subject of this review will be the many possible interactions between antibacterial agents and phagocytes, classified according to demonstrated or potential clinical relevance (e.g., neutropenia, intracellular accumulation, and modulation of bacterial virulence). A detailed review of direct in vitro effects will be provided for the various antibacterial drug families, followed by a discussion of the clinical relevance of these effects in two particular settings: immune deficiency and inflammatory diseases. The prophylactic and therapeutic use of immunomodulatory antibiotics will be considered before conclusions are drawn about the emerging (optimistic) vision of future therapeutic prospects to deal with largely unknown new diseases and new pathogens by using new agents, new techniques, and a better understanding of the phagocyte in particular and the immune system in general.

Interference of antibacterial agents with phagocyte functions: immunomodulation or "immuno-fairy tales"?

Professional phagocytes (polymorphonuclear neutrophils and monocytes/macrophages) are a main component of the immune system. These cells are involved in both host defenses and various pathological settings characterized by excessive inflammation. Accordingly, they are key targets for immunomodulatory drugs, among which antibacterial agents are promising candidates. The basic and historical concepts of immunomodulation will first be briefly reviewed. Phagocyte complexity will then be unravelled (at least in terms of what we know about the origin, subsets, ambivalent roles, functional capacities, and transductional pathways of this cell and how to explore them). The core subject of this review will be the many possible interactions between antibacterial agents and phagocytes, classified according to demonstrated or potential clinical relevance (e.g., neutropenia, intracellular accumulation, and modulation of bacterial virulence). A detailed review of direct in vitro effects will be provided for the various antibacterial drug families, followed by a discussion of the clinical relevance of these effects in two particular settings: immune deficiency and inflammatory diseases. The prophylactic and therapeutic use of immunomodulatory antibiotics will be considered before conclusions are drawn about the emerging (optimistic) vision of future therapeutic prospects to deal with largely unknown new diseases and new pathogens by using new agents, new techniques, and a better understanding of the phagocyte in particular and the immune system in general.

Antibiotics in the prevention and treatment of coronary heart disease

Seroepidemiology, pathology, and animal studies provide evidence for a possible association between Chlamydia pneumoniae infections and atherosclerosis, coronary heart disease, and myocardial infarction. If this association exists, then exposure to certain antibiotics may positively affect the clinical course after an acute ischemic cardiac event (secondary prevention) and affect the risk of developing a first-time myocardial infarction (primary prevention). Preliminary evidence from clinical trials suggests that treatment with new macrolide antibiotics may improve outcome after ischemic events, and evidence from a large case-control analysis indicates that exposure to tetracyclines or quinolones may reduce the risk of developing a first-time myocardial infarction. However, antibiotics for the treatment or prevention of ischemic heart disease must not be recommended yet. This review of published studies briefly summarizes the currently available literature on the effects of antibiotics on the risk of developing coronary heart disease and myocardial infarction.

The possible role of infections in acute myocardial infarction

Cardiovascular diseases, particularly coronary heart disease (CHD) and myocardial infarction (MI), are among the leading causes for morbidity and mortality in industrialized countries [2, 77]. During the past decades, various clinical or lifestyle risk factors for myocardial infarction such as hyperlipidemia, hypertension, obesity, lack of physical exercise and smoking have been identified. However, it is also recognized that these well-documented risk factors do not sufficiently account for all new cases of myocardial infarction [77]. Many patients with myocardial infarction have only a borderline risk profile or even lack known risk factors. The question arises: What additional risk factors may play a role in the etiology of atherosclerosis and ischemic heart disease?

The ketolide antimicrobial agent HMR-3004 inhibits neutrophil superoxide production by a membrane-stabilizing mechanism

We have investigated the membrane-stabilizing potential of the prototype ketolide antimicrobial agent, HMR-3004 (3.75-125 microM), as well as the effects of this agent on the production of superoxide by human neutrophils activated with FMLP, the calcium ionophore A23187, phorbol 12-myristate 13-acetate (PMA) or opsonized zymosan (OZ), each of which uses different transductional mechanisms to activate NADPH-oxidase. Membrane-stabilizing activity was investigated using a hemolytic procedure, while superoxide production was assayed by lucigenin-enhanced chemiluminescence. At concentrations of 3.75 microM and greater, HMR-3004 caused dose-related inhibition of superoxide production by neutrophils activated by all four stimuli of membrane-associated oxidative metabolism, which was not associated with cytotoxicity or superoxide-scavenging activity. At the same concentrations, HMR-3004 antagonized the hemolytic actions of the membrane-disruptive bioactive phospholipids, lysophosphatidylcholine (LPC), platelet-activating factor (PAF) and lyso-PAF. A mechanistic relationship between the membrane-stabilizing and the anti-oxidative properties of HMR-3004 was suggested by the observation that treatment of neutrophils with non-cytolytic concentrations of LPC antagonized the inhibitory effects of the ketolide on superoxide production by these cells. These membrane-stabilizing, anti-oxidative activities of HMR-3004 suggest that in addition to its antimicrobial properties, this agent possesses anti-inflammatory properties which are superior to those of the presently available macrolide and azalide agents.

Lack of association between first myocardial infarction and past use of erythromycin, tetracycline, or doxycycline

To evaluate the association of prior treatment with antibiotics active against Chlamydia pneumoniae with the risk for incident myocardial infarction, we conducted a population-based case-control study. We found that use of erythromycin, tetracycline, or doxycycline during the previous 5 years was not associated with risk for first myocardial infarction. These results suggest little or no association between the use of these antibiotics and the risk for first myocardial infarction in the primary prevention setting.

Sterically stabilized phospholipids attenuate human neutrophils chemotaxis in vitro

The purpose of this study was to determine whether sterically stabilized liposomes (SSL) and poly(ethylene glycol)-distearoylphosphatidylethanolamine (PEG-DSPE) attenuate polymorphonuclear neutrophils (PMNs) chemotaxis in vitro and, if so, whether incorporation of vasoactive intestinal peptide (VIP), a pleiotropic neuropeptide, on the surface of SSL amplifies SSL-induced responses. Using a modified blind-well chamber chemotaxis assay, we found that N-formyl-methionyl-leucyl-phenylalanine (FMLP; 0.1 microM) and zymosan opsonized with purified human complement (2 x 10(9) yeast wall particles/ml) elicit significant human PMNs chemotaxis (95+/-9 and 103+/-3 cells/high power field; p<0.05). These effects are significantly attenuated by SSL and PEG-DSPE (p<0.05). By contrast, aqueous VIP and VIP on SSL have no significant effects on FMLP- and zymosan-induced responses. We conclude that certain sterically stabilized liposomes and phospholipids attenuate human PMNs chemotaxis in vitro and that VIP does not modulate this response.

Azithromycin impact on neutrophil oxidative metabolism depends on exposure time

Several antimicrobial agents have already been investigated relating to their influence on neutrophil ROS generation. Azithromycin provides, a dose-related anti-oxidant effect, after 15 min incubation, with the stimulating agent FMLP, as well with PMA or S. aureus. This finding was however obtained with concentrations not considered in therapeutics. Since short incubation times are not representative of the physiological situation, and since azithromycin is characterized by prolonged high concentrations within phagocytes, the same experiments were performed over 2 and 4 h exposures. A time-dependent anti-oxidant effect was then reported. The maximum effect was obtained with PMA (IC50 were 856 and 30 micrograms/ml for 15 min and 4 h incubation times respectively). Time-dependent modifications of neutrophil oxidative metabolism seem to be correlated with intracellular concentrations. Depressed oxidative metabolism might be related neither to azithromycin cellular toxicity, nor to superoxide scavenging properties. By increasing exposure periods, therapeutic concentrations could therefore lead to an anti-inflammatory effect, potentially of clinical interest since associated with bacteriostatic activity.

Effect of dirithromycin on Haemophilus influenzae infection of the respiratory mucosa

Macrolides have properties other than their antibiotic action which may benefit patients with airway infections. We have investigated the effect of dirithromycin (0.125 to 8.0 microg/ml) on the interaction of Haemophilus influenzae with respiratory mucosa in vitro using human nasal epithelium, adenoid tissue, and bovine trachea. Dirithromycin did not affect the ciliary beat frequency of the nasal epithelium or the transport of mucus on bovine trachea, but dirithromycin (1 microg/ml) did reduce the slowing of the ciliary beat frequency and the damage to the nasal epithelium caused by H. influenzae broth culture filtrate. Amoxicillin (2 microg/ml) did not reduce the effects of the H. influenzae broth culture filtrate. H. influenzae infection of the organ cultures for 24 h caused mucosal damage and the loss of ciliated cells. Bacteria adhered to damaged epithelium and to a lesser extent to mucus and unciliated cells. Incubation of H. influenzae with dirithromycin at sub-MICs (0.125 and 0.5 microg/ml) prior to infection of the organ cultures did not reduce the mucosal damage caused by bacterial infection. By contrast, incubation of adenoid tissue with dirithromycin (0.125 to 1.0 microg/ml) for 4 h prior to assembling the organ culture reduced the mucosal damage caused by subsequent H. influenzae infection by as much as 50%. The number of bacteria adherent to the mucosa was reduced, although the tissue that had been incubated with dirithromycin (0.125 and 0.5 microg/ml) did not inhibit bacterial growth. This was achieved by a reduction in the amount of damaged epithelium to which H. influenzae adhered and a reduction in the density of bacteria adhering to mucus. We conclude that dirithromycin at concentrations achievable in vivo markedly reduces the mucosal damage caused by H. influenzae infection due to a cytoprotective effect.

Roxithromycin, clarithromycin, and azithromycin attenuate the injurious effects of bioactive phospholipids on human respiratory epithelium in vitro

The effects of the bioactive phospholipids (PL), platelet-activating factor (PAF), lyso-PAF, and lysophosphatidylcholine (LPC) on the beat frequency and structural integrity of human ciliated respiratory epithelium were studied in vitro, in the presence or absence of polymorphonuclear leukocytes (PMNL), the antimicrobial agents, roxithromycin, clarithromycin, and azithromycin and the antioxidative enzymes catalase and superoxide dismutase (SOD). All three PL caused dose-dependent slowing of ciliary beat frequency (CBF) and epithelial damage (ED) at concentrations > or = 1 microgram/ml, which were unaffected by inclusion of the antimicrobial agents and antioxidative enzymes. When epithelial strips were exposed to the combination of PMNL and PL, there was significant potentiation of ciliary dysfunction and ED, which was ameliorated by pretreatment of the PMNL with the antimicrobial agents or by inclusion of catalase, but not SOD. These results demonstrate that LPC, PAF, and lyso-PAF cause epithelial damage by direct mechanisms which are oxidant-independent, as well as by indirect mechanisms involving phagocyte-derived reactive oxidants. Macrolides and azalide antimicrobial agents may have beneficial effects on airway inflammation in asthma and microbial infections by protecting ciliated epithelium against oxidative damage inflicted by PL-sensitized phagocytes.