Biomedical subjects

M T Labro

Publications and source records attributed to M T Labro.

At least 19 recordsLinked to original sources

PubMed2000

Effect of proinflammatory cytokines on the interplay between roxithromycin, HMR 3647, or HMR 3004 and human polymorphonuclear neutrophils.

Cytokines, the hallmarks of infectious and inflammatory diseases, modify phagocyte activities and thus may interfere with the immunomodulating properties of antibacterial agents. We have investigated whether various proinflammatory cytokines (interleukin 1 [IL-1], IL-6, IL-8, gamma interferon, tumor necrosis factor alpha [TNF-alpha], and granulocyte-macrophage colony-stimulating factor [GM-CSF]) modify two macrolide properties, i.e., inhibition of oxidant production by polymorphonuclear neutrophils (PMN) and cellular uptake. Roxithromycin and two ketolides, HMR 3647 and HMR 3004, were chosen as the test agents. TNF-alpha and GM-CSF (but not the other cytokines) decreased the inhibitory effect of HMR 3647 only on oxidant production by PMN. Fifty percent inhibitory concentrations were, however, in the same range in control and cytokine-treated cells (about 60 to 70 microgram/ml), suggesting that HMR 3647 acts downstream of the priming effect of cytokines. In contrast, the impairment of oxidant production by roxithromycin and HMR 3004 was unchanged (or increased) in cytokine-treated cells. This result suggests that HMR 3004 (the strongest inhibitory drug, likely owing to its quinoline side chain) and roxithromycin act on a cellular target upstream of cytokine action. In addition, TNF-alpha and GM-CSF significantly (albeit moderately) impaired (by about 20%) the uptake of the three molecules by PMN. The inhibitory effect of these two cytokines seems to be related to activation of the p38 mitogen-activated protein kinase. Our data also illuminate the mechanism underlying macrolide uptake: protein kinase A- and tyrosine kinase-dependent phosphorylation seems to be necessary for optimal uptake, while protein kinase C activation impairs it. The relevance of our data to the clinical setting requires further investigations, owing to the complexity of the cytokine cascade during infection and inflammation.

Anti-Bacterial Agents↗

PubMed2000

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.

Adjuvants, Immunologic↗

PubMed1999

Mechanism underlying levofloxacin uptake by human polymorphonuclear neutrophils.

The mechanism of radiolabeled levofloxacin ([3H]levofloxacin) uptake by human polymorphonuclear neutrophils (PMNs) was investigated by a classical velocity centrifugation technique. PMNs were incubated with levofloxacin for 5 to 180 min under various conditions before centrifugation through an oil cushion. Radioactivity was measured in the cell pellet to determine the amount of cell-associated drug. The uptake of levofloxacin was moderate with a cellular concentration/extracellular concentration ratio of about 4 to 6. Levofloxacin accumulated in PMNs parallel to the extracellular concentration, without saturation, over the range of 2.5 to 200 mg/liter (linear regression analysis: r = 0.92; P < 0.001). The activation energy was low (36 +/- 7.2 kJ/mol). Levofloxacin uptake was increased in Ca(2+)-depleted, EGTA-containing medium by approximately 33% (P = 0.022), while Ni2+, a Ca2+ channel inhibitor, inhibited it in a concentration-dependent manner, with the concentration that inhibited 50% of control uptake being approximately 2.65 mM. Verapamil (an L-type Ca2+ channel inhibitor) and other pharmacologic agents which modify Ca2+ homeostasis did not modify levofloxacin uptake. Interestingly, Ca2+ and Mg2+ inhibited levofloxacin uptake in a concentration-dependent manner. EGTA, Ni2+, and verapamil did not modify levofloxacin efflux; thapsigargin, a Ca2+ pool-releasing agent, modestly increased the intracellular retention of levofloxacin. In addition, contrary to other fluoroquinolones, probenecid at 1 to 10 mM did not modify either levofloxacin uptake or efflux. These data are consistent with a mechanism of passive accumulation of levofloxacin in PMNs. Extracellular Ca2+ and Mg2+ may influence the structural conformation of levofloxacin or the lipophilicity of PMN membranes, thus explaining their effect on levofloxacin uptake.

Anti-Infective Agents↗

PubMed1998

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.

Anti-Bacterial Agents↗

PubMed1998

Anti-inflammatory activity of macrolides: a new therapeutic potential?

The important role played by macrolides in the chemotherapy of infectious diseases is well established, but there is still much speculation about their anti-inflammatory potential. A review of in-vitro and ex-vivo studies reported in the literature shows that macrolides have potentially relevant immunomodulatory effects. In-vitro data suggest that erythromycin A derivatives have a direct effect on neutrophil function and the production of cytokines involved in the inflammation cascade. The ex-vivo results indicate that short-term administration of macrolides may enhance the immune response while long-term administration results in immunosuppression. Further research is required to improve our understanding of the therapeutic activity of macrolides.

Adjuvants, Immunologic↗

PubMed1998

Interactions between HMR 3647, a new ketolide, and human polymorphonuclear neutrophils.

HMR 3647, a new ketolide, is active upon intracellular pathogens. We previously demonstrated that HMR 3004 (RU 64004), another ketolide, is highly concentrated by human polymorphonuclear neutrophils (PMNs). This prompted us to evaluate whether the presence of a 3-keto group instead of an L-cladinose, a neutral sugar characteristic of erythromycin A derivatives, confers peculiar pharmacokinetic properties with regard to cellular accumulation and efflux. After incubation with the radiolabelled drug, HMR 3647 uptake was determined by a velocity gradient centrifugation technique. HMR 3647 was avidly concentrated by PMNs, without saturation, over a 3-h incubation period, with cellular-to-extracellular concentration ratios of 31 +/- 4.2 at 5 min and up to 348 +/- 27.1 at 180 min. About 60% of HMR 3647 was located in the granular compartment; less than 6% was associated with the membranes. HMR 3647 gradually egressed from loaded cells placed in drug-free medium. Uptake was dependent on environmental temperature (activation energy, 128 +/- 9. 4 kJ/mol) but not on extracellular pH. HMR 3647 displayed Michaelis-Menten saturation kinetics with a mean Vmax of 2315 ng/2.5 x 10(6) PMNs/5 min and a mean Km of 117 mg/liter (144 microM). As already observed with erythromycin A-derived macrolides, extracellular Ca2+ was necessary for optimal uptake of HMR 3647. Interestingly, verapamil increased the uptake of HMR 3647 at 5 min, but this was followed by gradual inhibition at later incubation times, a phenomenon probably related to stimulation of drug efflux. The impact of intracellular accumulation of HMR 3647 on PMN functions was also investigated. In contrast to other erythromycin A derivatives, HMR 3647 only weakly triggered granule exocytosis, but it inhibited superoxide anion production in a time- and concentration-dependent manner, with concentrations which inhibited 50% of control response of 55 (67 microM) (5 min) and 30 (36 microM) (30 min) mg/liter for formyl-methionyl-leucyl-phenylalanine stimulation and 117 (143 microM) (5 min) and 44 (54 microM) (30 min) mg/liter for phorbol myristate acetate stimulation.

Anti-Bacterial Agents↗

PubMed1997

Erythromycin A-derived macrolides modify the functional activities of human neutrophils by altering the phospholipase D-phosphatidate phosphohydrolase transduction pathway: L-cladinose is involved both in alterations of neutrophil functions and modulation of this transductional pathway.

All erythromycin A derivatives, irrespective of the size of the lactone ring and the nature of the substituent, inhibit oxidant production by neutrophils and promote their degranulation. We demonstrate in this study that the L-cladinose at position 3 of the lactone ring is a key structure in the modulation of these two neutrophil functions, suggesting that this sugar (alone or combined with a lactone structure) interferes with cell target(s) involved in both oxidant production and exocytosis. Taking roxithromycin as an example of erythromycin A derivatives, we also found that these molecules interfered with the phospholipase D (PLD)-phosphatidate phosphohydrolase pathway in two ways. In nonstimulated neutrophils, roxithromycin and all L-cladinose-bearing molecules activated PLD, as reflected by 1-O-[3H]alkyl-2-acyl-phosphatidyl-ethanol production. In addition, these drugs induced an accumulation of 1-O-[3H]alkyl-2-acyl-phosphatidic acid (PA), but not 1-O-[3H]alkyl-2-acylglycerol. PA accumulation seems to be involved in the induction of exocytosis by macrolides, as the roxithromycin-induced release of granular enzymes was impaired strongly in the presence of ethanol. By contrast, in stimulated neutrophils, roxithromycin inhibited PLD activity and totally impaired 1-O-[3H]alkyl-2-acylglycerol production. The inhibition of diglyceride production by roxithromycin (not its descladinosyl derivative) could explain its inhibitory effect on oxidant production. The relevance of our data to the clinical situation, particularly the anti-inflammatory activity of these drugs, requires further investigation.

Diglycerides↗

PubMed1997

Cellular accumulation of the new ketolide RU 64004 by human neutrophils: comparison with that of azithromycin and roxithromycin.

We analyzed the uptake of RU 64004 by human neutrophils (polymorphonuclear leukocytes [PMNs]) relative to those of azithromycin and roxithromycin. RU 64004 was strongly and rapidly accumulated by PMNs, with a cellular concentration/extracellular concentration ratio (C/E) of greater than 200 in the first 5 min, and this was followed by a plateau at 120 to 180 min, with a C/E of 461 +/- 14.8 (10 experiments) at 180 min. RU 64004 uptake was moderately sensitive to external pH, and activation energy was also moderate (63 +/- 3.8 kJ/mol). RU 64004 was mainly located in PMN granules (about 70%) and egressed slowly from loaded cells, owing to avid reuptake. The possibility that PMN uptake of RU 64004 and other macrolides occurs through a carrier-mediated system was suggested by three key results. First, there existed a strong interindividual variability in uptake kinetics, suggesting variability in the numbers or activity of a transport protein. Second, macrolide uptake displayed saturation kinetics characteristic of that of a carrier-mediated transport system: RU 64004 had the highest Vmax value (3,846 ng/2.5 x 10(6) PMNs/5 min) and the lowest Km value (about 28 microM), indicating a high affinity for the transporter. Third, as observed previously with other erythromycin A derivatives, Ni2+ (a blocker of the Na+/Ca2+ exchanger which mediates Ca2+ influx in resting neutrophils) impaired RU 64004 uptake by PMNs, with a 50% inhibitory concentration of about 3.5 mM. In addition, we found that an active process is also involved in macrolide efflux, because verapamil significantly potentiated the release of all three macrolides tested. This effect of verapamil does not seem to be related to an inhibition of Ca2+ influx, because neither EGTA [ethylene glycol-bis (beta-aminoethyl ether)-N,N',N'-tetraacetic acid] nor Ni2+ modified macrolide efflux. The nature and characteristics of the entry- and efflux-mediating carrier systems are under investigation.

Anti-Bacterial Agents↗

PubMed1997

[Intracellular penetration of macrolides].

CELL PENETRATION: One of the main features of macrolides is their capacity to penetrate host cells. This property is the basis of their action against intercellular microorganisms and can explain characteristic pharmacokinetics as well as interference with cell metabolism. INTRACELLULAR CONCENTRATION: Erythromycin A derivatives with a single base group (roxithromycin) accumulate rapidly to a saturation point both the cytoplasm and in granulations. Intracellular concentrations of derivatives with two base groups do not reach saturation due to slow exflux. THERAPEUTIC ACTION: Because of their intracellular concentration, macrolides are indicated for the treatment of cell-associated pathogens. Exflux allows possible selective transfer into infected tissues. Macrolides also have an effect on functional activity of the host cells.

Animals↗

PubMed1997

The prohost effect of antimicrobial agents as a predictor of clinical outcome.

Apart from their direct antimicrobial activity, some antimicrobial agents may interfere in the complex host-microorganism interplay by modulating the natural response to invading pathogens. The three main aspects of this non-antibiotic effect (alteration of bacterial virulence, synergism with/impairment of the natural host response, impact on effector cell progenitors) will be briefly reviewed here, along with their potential incidence in the clinical outcome of infectious diseases.

Anti-Bacterial Agents↗

PubMed1996

Comparison of various macrolides on stimulation of human neutrophil degranulation in vitro.

Macrolide antibiotics are taken up and concentrated by host cells, particularly phagocytes, and are likely candidates to modify cell functions. In this study, we extended our previous work concerning the effect of three 14-membered-ring macrolides (dirithromycin, erythromycin and erythromycylamine) on human neutrophil exocytosis, and found that three other erythromycin A derivatives (roxithromycin, clarithromycin and the azalide, azithromycin) also triggered neutrophil degranulation in a time- and concentration-dependent manner. After 30 min of incubation, the correlation coefficients for concentration-dependence for roxithromycin were 0.885, 0.739 and 0.750 (P < 0.005) and for clarithromycin were 0.795, 0.599, 0.733 (P < 0.02), respectively, for lysozyme, beta-glucuronidase and lactoferrin release. Although the underlying mechanism was not elucidated, these and previous data suggest that intracellular accumulation is a prerequisite. Furthermore, comparison of the characteristics of macrolide-induced exocytosis with those of exocytosis triggered by the synthetic chemotactic stimulus FMLP suggested that different mechanisms are involved. In keeping with this possibility, we showed that combined treatment (macrolides plus FMLP) resulted in totally additive exocytosis of azurophilic but not specific granules. The clinical relevance of our data remains to be ascertained.

Analysis of Variance↗

PubMed1995

[Interaction between anti-infective agents and phagocytes].

Metchnikoff was one of the first to suggest the need for cooperation between phagocytes and therapeutic agents for the benefit of health. After the hopes raised by the discovery and the tremendous development of antimicrobials, there is now a creeping pessimism faced with the parallel evolution of resistance strategies in the microbial world. Interest has now turned to the use of immunomodulatory drugs, alone or combined with anti-infectious agents. Another tendency is based on the possibility that antimicrobials directly interfere with the host-microbe interplay. This review is aimed at summarizing our knowledge of the interactions between antimicrobial agents and the phagocyte, still a cornerstone in the natural defence system. Despite the problems inherent in the analysis and clinical relevance of effects observed in the test tube this developing area of research could provide new therapeutic solutions beyond the year 2000.

Anti-Infective Agents↗

PubMed1995

Role of extracellular calcium in in vitro uptake and intraphagocytic location of macrolides.

We compared the uptakes and intracellular locations of four 14-membered-ring macrolides (roxithromycin, dirithromycin, erythromycin, and erythromycylamine) in human polymorphonuclear neutrophils (PMNs) in vitro. Intracellular location was assessed by cell fractionation and uptake kinetics in cytoplasts (granule-poor PMNs). Trapping of dirithromycin within PMN granules (up to 80% at 30 min) was significantly more marked than the intracellular trapping of the other drugs (erythromycylamine, 45% +/- 5.1%; erythromycin, 42% +/- 3.7%; roxithromycin, 35% +/- 3.0%). A new finding was that, in the absence of extracellular calcium, the uptakes of all of the macrolides by PMNs and cytoplasts were significantly impaired, by about 50% (PMN) and 90% (cytoplasts). Furthermore, inorganic Ca2+ channel blockers inhibited macrolide uptake in a concentration-dependent manner, with 50% inhibitory concentrations of 1.6 to 2.0 mM and 29 to 35 microM, respectively, for Ni2+ and La3+. The intracellular distributions of the drugs were unchanged in the presence of Ni2+ and La3+ and in Ca(2+)-free medium supplemented with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. The organic Ca2+ channel blocker nifedipine had no effect on macrolide uptake, whereas verapamil inhibited it in a time- and concentration-dependent manner. These data show the importance of extracellular Ca2+ in macrolide uptake by phagocytes and suggest a link with Ca2+ channels or a Ca2+ channel-operated mechanism.

Anti-Bacterial Agents↗

PubMed1994

[Macrolides. New therapeutic prospects].

The aim of the development of semisynthetic derivatives was to overcome the problem of chemical stability of erythromycin A in acid medium, with less variability in gastro-intestinal absorption and leading to renewed interest in macrolides. The new macrolides have the same antibacterial spectrum as erythromycin A including Gram-positive and Gram-negative cocci, intracellular bacteria, mycoplasma, Campylobacter sp., Helicobacter pylori, mycobacteria spp., Gram-negative bacilli including Haemophilus influenzae, Bordetella pertussis, Pasteurella multocida, Gram-positive bacilli including Corynebacterium diphtheriae and anaerobic species. In vitro activity against Haemophilus influenzae is still a controversial subject. Macrolides are among the best tolerated antibacterial agents. Theoretically, macrolides could be given to a large range of patients even those suffering from underlying diseases. The new macrolides, roxithromycin, azithromycin, clarithromycin, dirithromycin, rokitamycin and miokamycin, are indicated for the treatment of upper respiratory tract infections and lower respiratory tract infections due to intracellular bacteria or Mycoplasma pneumoniae. Macrolides could be used as first line therapy for non-gonococcal urethritis, especially those due to Chlamydia trachomatis or Ureaplasma urealyticum. In pelvic inflammatory infections in which Chlamydia trachomatis is involved macrolides could also be used. Other non-conventional indications under discussion are H. pylori and Lyme's disease. Macrolides in combination with other antibacterials could be an alternative for Mycobacterium avium-intracellulare infections. The antiparasite effect of erythromycin has been known since the 1950s. Extensive experimental work is currently underway to determine the potential use of these drugs in this setting. Research during the 80s in the macrolide field, led to enhanced pharmacokinetic properties. Current research is focused on expanding the antibacterial spectrum and to overcome cross-resistance among 14-membered-ring macrolides.

Animals↗

PubMed1994

Cefdinir (CI-983), a new oral amino-2-thiazolyl cephalosporin, inhibits human neutrophil myeloperoxidase in the extracellular medium but not the phagolysosome.

Cefdinir, a new oral 2-amino-5-thiazolyl cephalosporin, inhibited the luminol-amplified chemiluminescence (LACL) response of human neutrophils stimulated by PMA but not opsonized zymosan, in a concentration-dependent but not time-dependent manner. The LACL response to opsonized zymosan in cytochalasin B-treated neutrophils was, however, inhibited by cefdinir. Various cephalosporins, regardless of the presence of a 2-amino-5-thiazolyl moiety, did not significantly alter the neutrophil LACL response triggered by PMA and zymosan. The LACL response induced by the calcium ionophore A23187 and FMLP was also impaired by cefdinir, and this impairment was increased in cytochalasin B-treated neutrophils. Superoxide anion generation by neutrophils, measured in terms of lucigenin-amplified chemiluminescence and cytochrome c reduction, was not altered. Spontaneous and FMLP-induced neutrophil degranulation, assessed by lysozyme and beta-glucuronidase release, were not modified by cefdinir. Furthermore, cefdinir inhibited LACL generation in cell-free systems consisting of H2O2, NaI, and either horseradish peroxidase or a myeloperoxidase-containing neutrophil extract. Orthodianisidine oxidation in these two acellular systems was inhibited by cefdinir. Cefdinir did not alter neutrophil bacterial killing at concentrations that inhibited myeloperoxidase-containing neutrophil extract-dependent reactions induced by soluble stimuli. Taken together, these data strongly suggest that cefdinir directly inhibits the activity of myeloperoxidase-containing neutrophil extract released into the extracellular medium during neutrophil stimulation by soluble mediators, but has no effect on that released into the phagolysosome during phagocytosis. This unusual property of a member of the beta-lactam family could be of interest in modulating the exaggerated inflammatory process often associated with infectious diseases.

Blood Bactericidal Activity↗

PubMed1994

Resolution of major protein kinase substrates in neutrophil cytosol in response to DAG/PS and arachidonic acid stimulation and the selective action of various protein kinase inhibitors.

Stimulation of human neutrophils induces phosphorylation of several cellular proteins. Human neutrophils possess calcium-dependent protein kinase C (PKC) alpha and beta isoforms and calcium-independent n isoforms. Little is known, however, of the physiological substrates of each isoform. In this study, we characterized the substrates of calcium-dependent and -independent PKC isoforms and the substrate of PKC activated by arachidonic acid. Furthermore, we found that the PKC inhibitor H-7 failed to inhibit phosphorylation of endogenous substrates of calcium-independent PKC activity. These results may help to understand the role of PKC in neutrophil activation and shed light on the different responses elicited by H-7 in intact cells.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1994

Investigation of dirithromycin and erythromycylamine uptake by human neutrophils in vitro.

Dirithromycin, a new semisynthetic 14-membered-ring macrolide was avidly concentrated by human neutrophils in a time- but not concentration-dependent manner with mean cellular/extracellular, concentration ratios (C/E) of 9 within the first 5 min and up to 47 at 120 min. Erythromycylamine, the hydrolysis product of dirithromycin, was concentrated significantly less by neutrophils, reaching C/E values of 4 and 19 (at 5 and 120 min). A point of interest was the interindividual variability in the antibiotic uptake kinetics; in particular, 7 out of 47 neutrophil samples from different healthy volunteers displayed very slow uptake of both drugs (C/E values at 30 min: dirithromycin, 5.8; erythromycylamine, 4.6). The reason(s) for this is unknown. The uptake of both drugs was decreased at acidic pH and increased at basic pH. Chloroquine, an antimalarial drug which is concentrated in and alkalinizes azurophilic granules, reduced uptake by half. Metabolic inhibitors (2-4 dinitrophenol, sodium fluoride, potassium cyanide and sodium azide) did not impair the uptake of either drug but, interestingly, ouabain, an inhibitor of membrane Na+/K+ ATPase activity, impaired uptake by about 30%. Competitive inhibitors of some transport systems identified on neutrophil membrane (nucleosides, D-glucose and various aminoacids) did not alter the uptake of either drug. Dirithromycin and to a lesser extent, erythromycylamine, reached intracellular concentrations much higher than those required to inhibit the growth of sensitive microorganisms. Although the mechanism of uptake is not clear, one interesting hypothesis involves trapping by protonation into acidic compartments of neutrophils.

Anti-Bacterial Agents↗

PubMed1994

Effects of dirithromycin and erythromycylamine on human neutrophil degranulation.

Dirithromycin and, to a lesser extent, erythromycylamine and erythromycin directly induced the release of three intragranular enzymes (lysozyme, lactoferrin, and beta-glucuronidase) from unstimulated human neutrophils. Macrolide-induced enzyme release was dependent upon the incubation time (30 to 180 min) and drug concentration. Dirithromycin was the most effective. At 120 min, release of lysozyme, beta-glucuronidase, and lactoferrin by macrolide (100 micrograms/ml)-treated cells, expressed as a percentage of total enzyme content, was, respectively, 58% +/- 8.3%, 52% +/- 10.7%, and 35% +/- 5.1% (dirithromycin); 42% +/- 3.9%, 28% +/- 5.8%, and 10% +/- 2.2% (erythromycylamine); and 35% +/- 4.0%, 19% +/- 4.3%, and 10% +/- 5.2% (erythromycin) (mean +/- standard error of the mean of three to eight experiments). The lowest macrolide concentrations which induced significant enzyme release were 10, 100, and 25 micrograms/ml, respectively, for dirithromycin, erythromycylamine, and erythromycin. Furthermore, we obtained evidence of a link between the prodegranulation effects of dirithromycin and erythromycylamine and the intragranular location of these drugs. Indeed, cell-associated drug levels increased for up to 60 min and then plateaued and declined substantially. Increasing the pH from 7 to 9 resulted in a parallel increase in drug uptake and the prodegranulation effect. Finally, when macrolide-treated neutrophils were disrupted by sonication and centrifuged, a correlation was found between lysozyme and beta-glucuronidase activities (both granule markers) and pellet-associated macrolide levels. Taken together, our results suggest that dirithromycin and erythromycylamine concentrate within neutrophil granules and then induce degranulation.

Anti-Bacterial Agents↗