Cytoprotection against neutrophil-delivered oxidant attack by antibiotics

[Modulatory effect of antimicrobial agents or aminoacids on the oxidative burst of polymorphonuclear neutrophils triggered by formylmethionyl-leucyl-phenylalanine (fMLP)]

We have compared the interplay of several antimicrobial agents and aminoacids on the neutrophil respiratory burst in response to formylmethionyl-leucyl-phenylalanine (fMLP), a chemoattractant. Mainly, an inhibitory effect has been observed in the penicillin family of agents and an enhancing effect in the cephalosporin family of agents. The molecules in which the sulfur numbered 1 in the 6-APA or 7-ACA nucleus was replaced by a carbon or an oxygen, had a different effect as compared with the other members of the family. The modulatory effects of ampicillin and cephalothine were not significant at a concentration lower than 10 mg/l and the effect of cephalothine looked maximum at 20-40 mg/l. If studies in cell-free systems demonstrated that the inhibitory effect of some antimicrobials could be due to a direct oxidant-scavenger activity mainly of HOCl, only hypotheses are proposed to explain the enhancing activity of the others. It could be in relation with (i) a synergistic effect upon fMLP receptor leading to an increase in H(2)O(2)/HOCl production or (ii) the generation of new oxydant products originating in cephalosporin lysis under HOCl attack, which would be able to react with luminol. The interplay of antimicrobial agents with the respiratory burst measured outside the cells probably has no therapeutic consequences because the bactericidal activity of neutrophils is achieved inside phagosomes where few agents are known to come into and where chemical conditions are different. On the opposite, in clinical use, this interplay could be interesting to study for a prevention of side effects.

In vitro inhibition of human neutrophil histotoxicity by ambroxol: evidence for a multistep mechanism

Neutrophils are major culprits for the protease/antiprotease imbalance during various lung diseases, that is, chronic obstructive pulmonary disease, cystic fibrosis, idiopathic pulmonary fibrosis and adult respiratory distress syndrome. Thus, these cells are presently considered an ideal target for the pharmacologic control of tissue injury during these diseases. This study was planned in order to investigate if ambroxol and its precursor bromhexine are actually capable of preventing alpha-1-antitrypsin (A1AT) inactivation by stimulated neutrophils and possibly to look into the mechanisms underlying this event. Ambroxol inhibited the production of superoxide anion by activated neutrophils, whereas bromhexine had no inhibitory effect. Ambroxol decreased the production of hypochlorous acid (HOCl) from activated neutrophils with high efficiency, whereas bromhexine had a modest activity. Ambroxol and bromhexine were capable of limiting the chlorination of monochlorodimedon by HOCl, displaying the capacity of directly scavenging the oxidant. Ambroxol decreased the release of elastase and myeloperoxidase from activated neutrophils, whereas bromhexine was ineffective. Ambroxol prevented the A1AT inactivation by neutrophils, whereas bromhexine was completely ineffective. Among drugs currently available for in vivo use in humans, ambroxol is unique by virtue of its ability to prevent neutrophil-mediated A1AT inactivation via inhibition of HOCl production as well as HOCl scavenging. Also taking into account its capacity for curbing elastase release, the drug displays the potential to lessen the burden of oxidants/proteases and to increase the antiprotease shield at the site of inflammation. Thus, ambroxol appears to be a good candidate for raising attempts to develop new therapeutic histoprotective approaches to inflammatory bronchopulmonary diseases.

Endotoxin neutralization and anti-inflammatory effects of tobramycin and ceftazidime in porcine endotoxin shock

Introduction

Antibiotics used for treatment of severe bacterial infections have been shown to exert effects on the inflammatory response in addition to their antibacterial effects. The aim of the present study was to investigate whether the biological effects of endotoxin in a porcine model could be neutralized by tobramycin, and whether tobramycin or ceftazidime was able to modulate the inflammatory response.

Method

Thirteen piglets were subjected to endotoxin infusion at an initial rate of 4 μg/kg per hour, which was reduced to 1 μg/kg per hour after 30 min. Before endotoxin infusion, the animals received saline (n = 4), ceftazidime (n = 5), or tobramycin (n = 4) at clinically relevant doses. Physiological parameters were measured and blood samples were taken hourly for 6 hours for analysis of tumour necrosis factor-α, IL-6 and endotoxin concentrations.

Results

All of the animals exhibited physiological signs of severe sepsis without major differences between the groups. Plasma endotoxin concentration was stable after 1 hour. There were no differences in endotoxin concentration or initial tumour necrosis factor-α and IL-6 concentrations between the groups. At 6 hours the IL-6 concentration was significantly lower in the ceftazidime group than in the saline group (P < 0.05), and in both the ceftazidime and the tobramycin groups there were significantly greater reductions from peak values (P < 0.05).

Conclusion

There was no neutralization of the biological effects of endotoxin in this porcine model. However, our data indicate a possible anti-inflammatory effect exerted by both ceftazidime and tobramycin, which manifested as a significantly greater reduction in IL-6 in comparison with the untreated group.

Oxygen consumption and electron spin resonance studies of free radical production by alveolar cells exposed to anoxia: inhibiting effects of the antibiotic ceftazidime

By EPR spectroscopy, we investigated free radical production by cultured human alveolar cells subjected to anoxia/re-oxygenation (A/R), and tested the effects of ceftazidime, an antibiotic previously demonstrated to possess antioxidant properties. Two A/R models were performed on type II pneumocytes (A549 cell line), either on cells attached to culture dishes (monolayer A/R model; 3.5 h of anoxia, 30 min of re-oxygenation) or after cell detachment (suspension A/R model; 1 h of anoxia, 10 min of re-oxygenation). Ceftazidime and selective inhibitors (SOD, Tiron, L-NMMA) were added before anoxia. Free radical production was assessed by the EPR spin trapping technique. Oxygen consumption was monitored, in parallel with EPR studies, in the suspension A/R model. The production of free radical species was demonstrated by the generation of PBN-radical adducts: (a(N) = 15.2 G) in the monolayer A/R model and a six-line EPR spectrum (a(N) = 15.7 G and a(H) = 2.7 G) in the suspension A/R model. A kinetic study performed by oximetry, in parallel with EPR spectroscopy, demonstrated marked alterations of the cell respiratory function and that the free radical production started during anoxia and increased during re-oxygenation. In the suspension A/R model, the amplitude of EPR spectra were decreased upon the addition of 200 U/ml SOD (37% inhibition), 0.1 mM Tiron (67% inhibition) and 1 mM L-NMMA (43% inhibition). Addition of 1 mM ceftazidime decreased the amplitude of EPR spectra (37% inhibition) in both A/R models. Complementary in vitro EPR studies demonstrated that CAZ scavenged the hydroxyl radical (produced by the Fenton reaction). The protective effect of ceftazidime in the cell model could thus be linked to its ability to scavenge superoxide anions, nitrogen-derived species and hydroxyl radicals.

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.

Cefoperazone prevents the inactivation of alpha(1)-antitrypsin by activated neutrophils

At sites of neutrophilic inflammation, tissue injury by neutrophil elastase is favored by phagocyte-induced hypochlorous acid-dependent inactivation of the natural elastase inhibitor alpha(1)-antitrypsin. In the present study, cefoperazone prevented alpha(1)-antitrypsin inactivation by neutrophils and reduced the recovery of hypochlorous acid from these cells. Moreover, the antibiotic reduced the free elastase activity in a neutrophil suspension supplemented with alpha(1)-antitrypsin without affecting the cells' ability to release elastase. These data suggest that the drug inactivates hypochlorous acid before its reaction with alpha(1)-antitrypsin, thereby permitting the antiprotease-mediated blockade of released elastase. In conclusion, cefoperazone appears to have the potential for limiting elastase-antielastase imbalances, attenuating the related tissue injury at sites of inflammation.

Antibacterial agents--phagocytes: new concepts for old in immunomodulation

The possibility that antibacterial agents, primarily directed against microorganisms, also modify host functions is widely recognized. While a knowledge of these non-antimicrobial effects of antibiotics, sometimes considered as 'side-effects', is necessary to prevent antibiotic-associated toxicity, the development of drugs derived from antibacterial agents for use in non-infectious diseases (e.g. motilins and antidiabetic drugs) is a new field of therapeutic research. Interactions between antibacterial drugs and the immune system may contribute to therapeutic efficacy in infectious diseases [1,2]. The immune system itself is a complex pyramid of redundant cellular factors/humoral effectors/mediators, whose fine regulation is just beginning to be unraveled. Phagocytes, ubiquitous and multifaceted cells are key components of cellular immunity, being involved both in immediate defences against non-self targets (pathogens, tumour cells, exogenous molecules, etc.) and in the regulation and triggering of specific immune responses. They are thus, prime targets of immune response modifiers. This review reconsiders the widely explored problem of interactions between antibacterial agents and phagocytes, focusing on future prospects in both infectious and non-infectious diseases.

Oxidant-scavenging activities of beta-lactam agents

The relative antioxidant effect of ampicillin, ceftazidime, ceftriaxone, and cefuroxime on oxygen-reactive species was examined in vitro using stimulated human polymorphonuclear neutrophils. There was no evidence that any of the beta-lactam agents tested had an effect on superoxide or H2O2 generation. In contrast, all of the beta-lactam agents prevented hypochlorous acid (HOCI) chlorination of 1,1-dimethyl-4-chloro-3,5-cyclo-hexanedione in a cell-free system at concentrations of < 10 microg/ml. Furthermore, all antibiotics provided dose-dependent protection against HOCI cytotoxicity to 16HBE140 bronchial epithelial cells. Taken together, these data indicate a possible therapeutic role for beta-lactam agents in protecting host tissues from HOCI-induced oxidative damage.

Immunomodulating effects of antibiotics: literature review

Antibiotics can interact directly with the immune system. This is a review of the immunomodulating effects of antibiotics. The Medline database on CD-ROM was searched for the years 1987 to 1994 using the following search string: "thesaurus explode antibiotics/all AND (thesaurus explode immune-system/drug effects OR thesaurus immune-tolerance/drug effects)." Aspects of the immune system studied were aspects of phagocyte functions: phagocytosis and killing, and chemotaxis and aspects of lymphocyte functions: lymphocyte proliferation, cytokine production, antibody production, delayed hypersensitivity and natural killer-cell activity. In order to quantify and to compare immunomodulatory properties of antibiotics we calculated an "immune index," defined as: number of positive statements--number of negative statements/total number of statements. Concerning phagocytosis, positive effects were observed for cefodizime, imipenem, cefoxitin, amphotericin B and clindamycin and negative effects for erythromycin, roxithromycin, cefotaxime, tetracycline, ampicillin and gentamicin. Clindamycin, cefoxition and imipenem induce enhancement of chemotaxis, whereas cefotazime, rifampicin and teicoplanin decrease chemotaxis. Regarding lymphocyte proliferation, cefodizime has the strongest stimulating effect, whereas tetracycline has the strongest negative effect. Except for erythromycin and amphotericin B the number of statements reported is too small to be conclusive for the interpretation of effects on cytokine production. Erythromycin and amphotericin B appear to stimulate cytokine production. As to antibody production, cefodizime has the strongest positive effect, whereas josamycin, rifampicin and tetracycline have marked negative effects. For delayed hypersensitivity and the natural killer-cell activity the number of statements is too small for any single antibiotic to be conclusive. There are three markedly immuno-enhancing antibiotics (imipenem, cefodizime and clindamycin) and eight markedly immuno-depressing antibiotics (erythromycin, roxithromycin, cefotaxime, tetracycline, rifampicin, gentamicin, teicoplanin and ampicillin).

Is there an unidentified defence mechanism against infection in human plasma?

The total peroxyl radical scavenging capacity (TRAP) of human plasma was measured from pneumonia patients and controls. TRAP and its main components, ascorbic acid, alpha-tocopherol, uric acid or protein thiol groups, were unaltered, but the concentration of unidentified antioxidants in pneumonia patients was significantly reduced. Our results indicate that human plasma may contain so far unidentified antioxidants depleted in infection.

Treatment of pregnant mice with antibiotics modulates the humoral response of the offspring: role of prenatal and postnatal factors

This study was designed to determine the role of prenatal and postnatal factors underlying altered humoral response of the offspring of mice treated with antibiotics during pregnancy. Pregnant random-bred NMRI mice were administered i.p. from the 11th to 15th day of pregnancy with a mixture of ampicillin and cloxacillin (2:1) in a daily dose of 21 mg/kg body weight. The litters of experimental and control mothers were cross-fostered at birth and the offspring were immunized on the 23rd or 24th postnatal day with SRBC. The primary humoral response was assayed using spectrophotometric determination of SRBC lysis mediated by anti-SRBC IgM antibodies produced by spleen cells. The offspring born of saline-treated mothers and transferred to mothers treated with antibiotics, as well as the offspring born to mothers treated with antibiotics and transferred to mothers treated with saline, produced significantly higher amounts of spleen anti-SRBC IgM than the control offspring. The results suggest that the immune response of the offspring was modulated by both the prenatally and postnatally acting factors, the latter being mediated by effects of antibiotics on the maternal organism.

Evaluation of the role of reactive oxygen species in the interactive toxicity of carbide-cobalt mixtures on macrophages in culture

The lung toxicity of a carbide-cobalt mixture is more important than that of each individual component; the mechanism of this interaction is not understood. The capacity of cobalt metal particles alone and mixed with different carbides to generate hydroxyl radicals was examined with the deoxyribose assay. In a chemical system, cobalt ions and cobalt metal particles (Co) were found to catalyse the degradation of deoxyribose in the presence of hydrogen peroxide. Carbides were able to directly oxidize deoxyribose, but their respective activities did not support such a mechanism to explain the carbide-cobalt interactive toxicity, since there was no direct relationship between deoxyribose degradation ability and cytotoxicity toward macrophages. Tungsten, niobium, titanium and chromium carbides (interactive carbides) were only weak oxidants and conversely molybdenum, vanadium and silicon carbides (non-interactive carbides) were the most potent ones. The ability of cobalt metal to produce hydroxyl radicals in the presence of hydrogen peroxide was not increased by tungsten carbide. The role of reactive radical formation in the toxicity of these particles was further assessed in a macrophage culture model. Catalase (4000 U/ml), superoxide dismutase (300 U/ml), sodium azide (1 mM), sodium benzoate, mannitol, taurine and methionine (all 20 mM) were all unable to protect against the cytotoxic effects of cobalt ions and cobalt metal alone or mixed with tungsten carbide. In conclusion, no evidence was found that production of reactive oxygen species contributes to the elective toxicity of carbide-cobalt mixtures.