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Objectives: The aim was to compare the in vitro effects of amoxicillin and ampicillin on the oxidative metabolism of polymorphonuclear neutrophils (PMNs)., Methods: Superoxide radical anion production by PMNs, stimulated or not by various exogenous stimulants and in contact with increasing antibiotic concentrations, was measured using spectrophotometric methods., Results: Whereas a pro-oxidative action of amoxicillin on PMNs was obtained without exogenous stimulation or with opsonized zymosan (OZ), the O(2)(-) production by PMNs incubated with ampicillin did not increase significantly., Conclusions: This amoxicillin pro-oxidative effect could be due to the activation of the PMN NADPH oxidase, to its induction by a membrane effect or via the OZ pathway. It probably reinforces amoxicillin intrinsic bactericidal action and might partly explain the severe rashes sometimes occurring with amoxicillin treatment.

The beta-adrenoreceptor blocker labetalol has demonstrated important antioxidant properties in vitro that inhibit superoxide anion production during normal leukocyte oxidative metabolism. This study investigated the in vitro and ex vivo effects of labetalol on respiratory burst in rabbit neutrophils. The production of superoxide anions was examined in activated purified rabbit neutrophils after intravenous administration of labetalol (4.0 mg/kg of body weight). At a concentration up to 200 mg/L, labetalol did not demonstrate any cytotoxic effects on neutrophils, as determined by enzyme lactate dehydrogenase activity. In the cell-free system, labetalol demonstrated no significant activity, but in formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated rabbit neutrophils, labetalol demonstrated concentration-dependent antioxidant activity. The in vitro 50% inhibitory concentration (IC50) with the fMLP stimulus was 16.5+/-0.21 mg/L in the rabbit neutrophils and 13.2+/-0.16 mg/L in the human neutrophils. In the fMLP-stimulated rabbit polymorphonuclear leukocytes, labetalol demonstrated its peak inhibitory activity (47%) 3 hours after administration. The mechanism by which labetalol acts in the treatment of hypertension may occur from an interaction in the signaling pathway of protein kinase C activation. The antioxidant properties demonstrated in this mechanism contribute to the drug's antihypertensive action and thus, may reduce the risk of injuries inflicted by reactive oxygen species involved in the pathogenesis of hypertension.

Respiratory burst leads polymorphonuclear neutrophils (PMN) to produce reactive oxygen species (ROS) such as superoxide anions (O(2)(o-)), hypochlorous acid (HOCl) and hydrogen peroxide (H(2)O(2)) which may possess deleterious effects for the organism. Rosa canina fruits are well known to contain a large amount of vitamin C which is antioxidant. This study was focused on the polyphenolics contained in rose hips to evaluate their antioxidative properties. We prepared a rose hip extract deprived of vitamin C. The extract contained mainly phenolics such as proanthocyanidins and flavonoids. We investigated its effects directly against (O(2)(o-)), HOCl and H(2)O(2) and investigated its effects on isolated PMN. For that, in vitro inflammatory conditions were reproduced by stimulating PMN with stimuli having different transductional pathways, in order to determine a possible mechanism of action. The results showed that the extract can inhibit ROS tested in acellular and cellular systems. The IC(50) obtained were 5.73 mg/L, 1.33 mg/L and 2.34 mg/L respectively for (O(2)(o-)), HOCl and H(2)O(2) in acellular experiments. For cellular experiments, the IC(50) were quite similar. Thus, the extract did not present an effect on PMN metabolism. Therefore, the antioxidative effects of Rosa canina are due not only to vitamin C but also to polyphenolics., (Copyright 2002 John Wiley & Sons, Ltd.)

Dirithromycin is a 14-membered macrolide antibiotic, well known to yield high intragranulocytic levels after several hour exposure. We chose therefore to investigate oxidative metabolism after prolonged incubation periods with neutrophils. Neutrophil generation of reactive oxygen species, represented by superoxide anion, was assessed after fMLP or Staphylococcus aureus-induced activation of the respiratory burst. Cellular uptake of the drug was assessed concurrently, in order to attempt a correlation with time-dependent modifications of the cellular oxidative status. For 1 hour exposure time, a pro-oxidant effect was reported for lower concentrations, achievable during therapeutic administration, whereas the highest ones promoted a potent anti-oxidant effect. After prolonged incubation times, the anti-oxidant effect alone was reported, with time-dependent modifications of IC50 values. These values could be correlated with intracellular accumulation of the drug. The anti-inflammatory activity reported here for high dirithromycin concentrations, could be nevertheless clinically relevant, since dirithromycin cellular uptake extends beyond 4 hours.

In response to phagocytosis of microbes or chemical stimuli, neutrophils generate reactive oxygen species which represent the major bactericidal mechanism of these cells. We have investigated the influence of aminoglycosides (amikacin, gentamicin, netilmicin and tobramycin), antibiotics with a marked concentration-dependent killing effect, on the human neutrophil oxidative burst represented by the release of hydrogen peroxide. This study was performed using time-dependent cellular experiments and a cell-free system. In the cellular model, 2-h incubation with amikacin (ranging from 10 mg/l to 1 g/l), enhanced hydrogen peroxide release by stimulated human neutrophils. At higher concentrations (1 to 5 g/l), hydrogen peroxide production was decreased. No significant effects were observed with the other aminoglycosides at concentrations ranging from 10 mg/l to 2.5 g/l. The pro-oxidant activity of amikacin may be due to a cellular mechanism through oxidative metabolism of human neutrophils as demonstrated in the cell washing experiment, whereas the antioxidant activity observed for higher concentrations may be a result of a scavenging effect as demonstrated in the cell-free system. The enhanced of hydrogen peroxide production observed for therapeutic concentrations of amikacin could be a beneficial effect for neutrophil bactericidal functions.

Some proteases (particularly elastase) and metabolites of very reactive oxygen species (superoxide anion, hydrogen peroxide, hypochlorous acid and hydroxyl radicals) are generated by polymorphonuclear neutrophils (PMNs) during inflammatory disorders. Divalent cations, especially calcium (Ca2+) play an important regulatory role in the different PMNs functions. The aim of this study is to determine the role of extracellular calcium during the liberation of elastase and of reactive oxygen species production by human PMNs. Consequently, in order to stimulate PMNs, phorbolmyristate acetate (PMA), formyl-methionyl-leucyl-phenylalanine (fMLP) and opsonized zymosan (OZ) have been used. PMNs stimulated by OZ did not release elastase to reverse the PMA and fMLP systems. The production of elastase by PMNs stimulated by PMA to reverse the fMLP system is independent from the extracellular calcium, between 0.0 and 1.5 mM. With various higher concentrations of calcium, varying from 1.5 to 4.0 mM, the release of elastase by PMNs stimulated by PMA is extracellular calcium-dependent to reverse the fMLP system. The superoxide anion (O2-) generated by PMNs activated by fMLP is dependent from the extracellular calcium in the medium, whereas O2- production by PMA or OZ stimulated neutrophils was extracellular calcium-independent. These observations suggest that an influx of calcium may play an important role in the production of elastase and in the capacity of PMNs stimulated by fMLP to produce O2- to reverse the PMA and OZ systems.

1. The effects of bisindolylmaleimide GF 109 203X, reported to be a potent and highly selective inhibitor of protein kinase C (PKC), have been investigated on some human neutrophil functions. 2. GF 109 203X prevented O.2- production by NADPH-oxidase whatever the stimulus used for polymorphonuclear neutrophil (PMN) activation: directs PKC activators like phorbol myristate acetate (PMA) and dioctanoylglycerol, calcium ionophore (A23187), or receptor agonists like fMet-Leu-Phe (fMLP) and opsonized zymosan. 3. The effect of GF 109 203X was also examined on elastase exocytosis by neutrophils. PMA-mediated release was prevented by GF 109 203X. However, GF 109 203X had no effect on exocytosis induced by A23187 and the effect of this compound on the fMLP response changed according to its concentration. 4. These data suggest that PKC might be essential for stimulus-mediated O.2- production and also that PKC plays only a minor role in elastase secretion as compared to the role of the cytosolic calcium level.