Human polymorphonuclear neutrophils (PMN), reactive oxygen species (ROS) and inflammatory reactions are closely interrelated, and increasing attention is being given to the search for new synthetic or natural antioxidant agents, capable of reducing ROS and consequent inflammation. It has been claimed that bisabolol (a monocyclic sesquiterpene alcohol) has an antioxidant/anti-inflammatory activity, but this has almost exclusively been investigated using chemical or biochemical tests. We studied the ability of bisabolol to interfere with ROS production (luminol-amplified chemiluminescence, LACL) during human PMN respiratory bursts induced by both corpusculate(Candida albicans)and soluble stimulants (N-formyl-methionyl-leucyl-phenylalanine, fMLP). LACL was also used to test cell-free systems (SIN-1 and H2O2/HOCl– systems) in order to investigate the presence of scavenging activity. After C. albicans stimulation, significant concentration-dependent LACL inhibition was observed at bisabolol concentrations ranging from 7.7 to 31 μg/ml; after the fMLP stimulus, significant LACL inhibition was observed at bisabolol concentrations ranging from 3.8 to 31 μg/ml. A similar effect was observed in the SIN-1 and H2O2/HOCl– systems. These findings draw the attention to the possible medical use of bisabolol as a means of improving the antioxidant network and restoring the redox balance by antagonising oxidative stress.
Reactive oxygen species released by activated polymorphonuclear leukocytes as an expression of their defensive function are considered to be a major source of the cytotoxic oxidant stress, that triggers a self-sustaining phlogogenic loop in the respiratory system. N-Acetylcysteine (CAS 616-91-1, NAC), a known mucolytic drug, possesses also antioxidant properties, but it undergoes a rapid and extensive first-pass metabolism resulting in low tissue availability. Thus to further improve the NAC bioavailability a single oral administration of 1200 mg NAC has been recently proposed. This study has been performed to investigate in vitro by means of luminol amplified chemiluminescence the ability of the concentration of 35 mumol/l NAC available after single oral administration of 1200 NAC to interfere with human neutrophil oxidative burst evoked by both corpuscolate and soluble stimulants, in comparison with 16 mumol/l NAC, the serum concentration obtainable after single oral administration of 600 mg NAC. At concentrations of 16 and 35 mumol/l, NAC significantly reduced in a concentration-dependent manner the activation of polymorphonuclear neutrophils (PMNs) oxidative bursts induced by all of the stimulants (C. albicans, formyl-methionyl-leucyl-phenylalanine (fMLP), phorbol myristate acetate (PMA)). This effect was also present in cell-free systems, thus confirming the scavenger activity of these two concentrations of NAC. The fact that no effects were seen on PMN phagocytosis and bacterial killing indicates that NAC has no negative influence on other PMN functions such as antimicrobial activity.
Activated neutrophils can release superoxide anion and nitric oxide (NO), which subsequently combine with each other to yield peroxynitrite anions, powerful and harmful oxidants that preferentially mediate the oxidation of the thiol groups in proteins and non-protein molecules. These oxidants play a direct role in the inflammatory process in chronic obstructive pulmonary disease and asthma by increasing the number of neutrophils and macrophages that induce a self-sustaining phlogogenic loop. Budesonide (BUD) and erdosteine (a muco-active drug which, after metabolization, produces an active metabolite (Met I) with a sulfhydryl group) are both active in reducing the release of superoxide anion, NO and peroxynitrite, and can be administered to patients with respiratory diseases. The aim of this study was to investigate the possible synergistic in vitro effect of BUD and Met I on chemiluminescence generation during fMLP-stimulated respiratory bursts of human neutrophils with the NO donor L-arginine, added to the incubating medium. The investigated BUD concentrations ranged from 6 × 10–8 to 1 × 10–6 mol/l in logarithmic scale and a significant and progressive reduction in luminol-amplified chemiluminescence (LACL) was observed at concentrations ranging from 2.5 × 10–7 to 1 × 10–6 mol/l. The investigated concentrations of Met I varied from 0.62 to 10 µg/ml. No significant changes were observed at 0.62, 1.25, and 2.5 µg/ml, but a significant decrease in LACL was observed at 5 and 10 µg/ml. When the two drugs were combined, there was a greater significant decrease in LACL versus the single drugs with the combinations of BUD 1 × 10–6 mol/l plus Met I 10 µg/ml, BUD 5 × 10–7 mol/l plus Met I 5 µg/ml, BUD 2.5 × 10–7 mol/l plus Met I 2.5 µg/ml, and BUD 1.25 × 10–7 mol/l plus Met I 1.25 µg/ml. A further interesting finding was that the combination of BUD 2.5 × 10–7 mol/l plus Met I 2.5 µg/ml and BUD 1.25 × 10–7 mol/l plus Met I 1.25 µg/ml significantly decreased LACL, whereas the single concentrations had no significant effect, thus indicating the possibility of extending the duration of the effect. Our findings indicate a synergistic antioxidant effect when BUD and Met I are given together, which is of interest for counteracting the airway phlogosis involved in many respiratory diseases.
Polymorphonuclear neutrophils (PMNs) can generate superoxide anions and nitric oxide (NO), which is not only an important mediator of various cellular activities, but can also react with superoxide anions to produce peroxynitrite anions (ONOO–). Peroxynitrite is a potent and potentially toxic oxidant that damages various types of biomolecules. It preferentially mediates the oxidation of thiolic groups in protein and non-protein molecules, thus altering their functions. The aim of this study was to examine whether, in addition to its ability to reduce the respiratory bursts of human PMNs, the SH metabolite I (Met I) of erdosteine, can interfere with NO and NO-derived peroxynitrite production, thus extending its antioxidant activity. This was done by means of the luminol amplified chemiluminescence (LACL), which has been widely used to detect the production of reactive oxidant species (ROS) by PMNs under various conditions. At 5 and 10 µg/ml, Met I significantly reduced LACL after fMLP and PMA stimulation. When L-Arg was added to the reaction medium, as a NO donor, the chemiluminescence of fMLP increased by up to 67% and that of PMA by up to 132%, but was once again significantly reduced by 5 and 10 µg/ml of Met I. In a cell-free system, the use of linsidomine (SIN-1) makes it possible to investigate the behavior of LACL induced by peroxynitrite release, which was significantly reduced by Met I concentrations ranging from 1.25 to 10 µg/ml. Our findings indicate that Met I, a molecule with a SH group, reacts with ROS, NO and NO-derived peroxynitrite, and has both antioxidant and scavenging activity. This is of interest for the strategy of protecting against damage induced by radical species in the pulmonary cell environment, in which they can induce a phlogogenic loop, and suggests that adding exogenous thiols may be useful in antagonizing the toxic effects of reactive molecules on endogenous thiols.
The entry of an antibiotic into phagocytes is a prerequisite for its intracellular bioactivity against susceptible facultative or obligatory intracellular microorganisms. Brodimoprim is a dimethoxybenzylpyrimidine that has recently entered into clinical use, and its uptake into and elimination from human polymorphonuclear neutrophils (PMNs), together with its effects on normal phagocytic and antimicrobial mechanisms, have been investigated. Brodimoprim uptake by PMNs was determined by a velocity-gradient centrifugation technique under various experimental conditions and was expressed as the ratio of the intracellular to the extracellular drug concentration (C/E) in comparison with the C/E of trimethoprim, which was used as a control drug. After incubation with 7.5 micrograms of brodimoprim per ml, PMNs accumulated brodimoprim (C/E, 74.43 +/- 12.35 at 30 min) more avidly than trimethoprim (C/E, 20.97 +/- 6.61 at 30 min). The cellular uptake of brodimoprim was not affected by temperature, 2,4-dinitrophenol, or potassium fluoride and was increased with an increase in the pH of the medium. It was reduced in formaldehyde-killed PMNs. The efflux of brodimoprim was very rapid (46% after 5 min). The liposolubility of brodimoprim was about three times that of trimethoprim, as was the uptake. Therefore, a possible passive transmembrane diffusion mechanism might be proposed. Brodimoprim did not decrease either phagocytosis or phagocyte-mediated bactericidal activity, nor did it affect oxidative burst activity, as investigated by luminol-amplified chemiluminescence. On the basis of the pharmacokinetic data for brodimoprim, the concentration of 7.5 micrograms/ml was chosen as the highest concentration attainable in serum by oral therapy, and at this concentration of brodimoprim, the amount of drug that penetrated into PMNs was able to maintain its antimicrobial activity without interfering with the functions of the PMNs.
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