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M T Labro

Publications and source records attributed to M T Labro.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1994

[Experimental evaluation of antibiotics as immunomodulators].

Since the pioneer work by Metchnikoff, the goal of cooperation between therapeutics and the host defence system (HDS) has been sought after. This area of research received less attention after the introduction of antibiotics. Although, the predictive efficacy of antibacterial agents (ABA) is still evaluated in terms of MICs, MBCs, and pharmacokinetics, much evidence derived from clinical studies underlines the need for synergy between HDS and these drugs to obtain optimal therapeutic efficacy. The analysis of the immunomodifying properties of ABA has come under intense study. The majority of ABA does not substantially affect the functioning of the immune system at least in vivo, despite in-vitro observations of enhancement/inhibition of various immune parameters by some cephalosporins, macrolides, cyclins, aminoglycosides, etc. By contrast, chloramphenicol, sulphonamides and various beta-lactams may be responsible for drug-induced neutropenia whereas macrolides and quinolones, due to their high phagocytic uptake, synergize with phagocytes to destroy intracellular pathogens. Recently, the concept of Biological Response Modifier (BRM)-antibiotics has come under the limelight with the introduction of cefodizime, a new parenteral cephalosporin, which seems to be endowed with immunomodulating properties. This latter aspect has been demonstrated in vitro (potentiation of the phagocyte antimicrobial activity), ex vivo in immunocompromised animals and humans (restoration of various immune parameters) and in vivo (infection models using both sensitive and resistant species). Although the underlying mechanism has not been elucitated, the chemical structure responsible for this BRM activity has been recognized as the thio-thiazolyl moiety at C3 position of the cephem nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)

Adjuvants, Immunologic↗
PubMed1993

Modulation of human polymorphonuclear neutrophil function by macrolides: preliminary data concerning dirithromycin.

Polymorphonuclear neutrophils (PMN) play a prominent role in the host response to infectious diseases. One major bactericidal mechanism used by these cells is the production of reactive oxygen species during what is referred to as the oxidative burst. However, excessive oxidant generation can also be involved in cell and tissue damage associated with severe inflammatory reactions. Macrolide antibiotics are able to penetrate and concentrate within phagocytes and have been successfully used to treat infections due to facultative intracellular pathogens. However, intracellular accumulation of macrolides with possible alkalinization of cellular compartments may interfere with normal cell function. In-vitro and ex-vivo data suggest that macrolides affect various phagocytic functions. This paper presents an overview of the published data concerning the modulation of neutrophil function by macrolides. Preliminary data concerning the in-vitro modulation of the neutrophil oxidative burst by dirithromycin and its metabolite, erythromycylamine, are also discussed.

Anti-Bacterial Agents↗
PubMed1992

Inhibition of human neutrophil protein kinase C activity by the antimalarial drug mefloquine.

Mefloquine (alpha-(2-piperidyl)-2,8-bis(trifluoromethyl)-4-quinolinemethanol) , an antimalarial drug, has been shown to inhibit human neutrophil functions, particularly oxygen-dependent bactericidal activity. Since calcium- and phospholipid-dependent protein kinase C (PKC) has a central role in the regulation of this function, we hypothesized that its activity might be altered by mefloquine. We found that mefloquine directly inhibited PKC in a dose-dependent manner, with an IC50 of 45 microM. This inhibition appeared to be non-competitive with respect to ATP, histone and phosphatidylserine. In addition, mefloquine inhibited the binding of [3H]phorbol 12,13 dibutyrate to PKC, indicating that it interacts with the regulatory domain of PKC. By contrast, mefloquine had little or no effect on neutrophil cAMP-dependent protein kinase or its catalytic subunit. Phorbol myristate acetate-induced protein phosphorylation in intact neutrophils was also inhibited by preincubation with mefloquine at concentrations similar to those inhibiting superoxide anion production. These data suggest that inhibition of neutrophil functions by mefloquine may be due to the inhibition of cellular PKC and that mefloquine could have further biological effects in situations in which PKC is involved.

Dose-Response Relationship, Drug↗
PubMed1992

Immunological evaluation of cefodizime: a unique molecule among cephalosporins.

The immunomodulatory properties of cefodizime, a new aminothiazolyl cephalosporin, are reviewed. Cefodizime displays in vitro and ex vivo stimulatory effects on phagocyte bactericidal function. It also increases certain lymphocyte responses, including delayed type hypersensitivity and antibody production. In addition, it restores various immune functions in immunocompromised animals and humans. The immunomodulating activity of this drug is further supported by its in vivo efficacy in experimental models of infections using cefodizime-sensitive or -resistant pathogens. Cefodizime appears to be a promising molecule, exhibiting potent antimicrobial activity and exerting potentially beneficial effects on the immune system.

Animals↗
PubMed1992

[Alteration of bacteria induced by subinhibitory concentrations of cefixime: consequences on bactericidal activity of human polynuclear neutrophils].

Subinhibitory concentrations of most parenteral cephalosporins have been reported to alter bacterial infectivity and, in particular, to increase the susceptibility of altered bacteria to the killing effects of polymorphonuclear neutrophils (PMN). Few data on this issue are available for oral cephalosporins. This study investigated the effects of sub-MIC concentrations of the new oral cephalosporin cefixime on two bacterial targets, i.e., S. aureus 209P (MIC 20 mg/l) and E. coli K12 (MIC 0.15 mg/l). After overnight incubation (18 hours) with 10 or 5 mg/l cefixime, susceptibility of S. aureus to the killing effects of PMNs was increased two-fold as compared with control organisms and susceptibility to the O2-independent PMN bactericidal system (PMN extract) was also increased. In contrast, the susceptibility of E. coli to PMN and to cell-free bactericidal systems was identical for cefixime-exposed strains (0.1 and 0.05 mg/l) and for unexposed controls. However, cefixime-exposed E. coli were filamentous, suggesting that bactericidal efficacy in terms of the bacterial mass eliminated was enhanced in exposed strains. These data show that low levels of cefixime are capable of producing major alterations in susceptible and resistant bacteria and of increasing their susceptibility to PMN. These effects may be relevant in vivo, in particular when low concentrations of antibiotics persist over long periods in infected sites.

Anti-Infective Agents, Urinary↗
PubMed1991

Effects of anti-infectious agents on polymorphonuclear neutrophils.

Polymorphonuclear neutrophils play a crucial role in host defences against infectious diseases. New trends in anti-infectious therapy require knowledge of the possible interactions between the drugs and the natural defence system. This overview summarizes some of the in vitro data on the effects of anti-infectious agents on neutrophils. The relevance for the clinical situation is discussed.

Anti-Bacterial Agents↗
PubMed1991

Effect of monodesethyl amodiaquine on human polymorphonuclear neutrophil functions in vitro.

We have previously observed that the antimalarial drug amodiaquine impairs the human polymorphonuclear neutrophil (PMN) oxidative burst in vitro. However, the drug acted at a concentration of 100 micrograms/ml, far higher than that which is achievable therapeutically. Since amodiaquine is extensively metabolized into monodesethyl amodiaquine, we investigated whether the metabolite modified PMN functions at lower concentrations than amodiaquine does. Monodesethyl amodiaquine strongly depressed PMN chemotaxis and phagocytosis at concentrations as low as 10 micrograms/ml. This inhibition was reversed by washing out the drug. The PMN oxidative burst was markedly depressed by monodesethyl amodiaquine, whatever the assay technique (luminol-amplified chemiluminescence, lucigenin-amplified chemiluminescence, myeloperoxidase activity) or stimulus used (opsonized zymosan, phorbol myristate acetate, formylmethionyl leucyl phenylalanine). There were extreme interindividual variations in sensitivity to the depressive effect of monodesethyl amodiaquine when the PMN oxidative burst was assayed in terms of luminol-amplified chemiluminescence or lucigenin-amplified chemiluminescence. PMN samples were divided into two groups on the basis of the MIC of the drug: 60% of the samples were "highly sensitive," being strongly inhibited at concentrations as low as 0.1 micrograms/ml (obtained during therapy), whereas the "moderately sensitive" samples were inhibited at concentrations of 10 micrograms/ml and above. The difference between the two groups was highly significant. This PMN sensitivity to the inhibitory effect of the drug was not related to intrinsic oxidative metabolism. Our data indicate that monodesethyl amodiaquine, the main metabolite of amodiaquine, has a far stronger inhibitory effect on various PMN functions in vitro than the parent drug, warranting relevant in vivo studies.

Amodiaquine↗
PubMed1991

Quinine uptake by human polymorphonuclear neutrophils.

The antimalarial drug quinine has been shown to impair human polymorphonuclear leukocyte (PMN) functions. To gain insight into the mechanism of this phenomenon, we investigated quinine uptake by PMN with a fluorometric assay based on the fluorescence properties of this drug. After 30 min of incubation at 37 degrees C in the presence of 1 and 10 micrograms of quinine per ml, PMN-associated quinine reached 90 +/- 6 and 780 +/- 150 ng/2.5 x 10(6) PMN, respectively, giving a cellular-to-extracellular concentration ratio of 140 to 150. A steady state was reached within 5 min. Uptake was partially dependent on temperature, cell viability, and extracellular pH. Fractionation studies showed that 30 to 40% of the PMN-associated quinine was located in the particulate fraction. The efflux of PMN-associated quinine was rapid and complete when the incubation mixture was replaced by drug-free medium. These data suggest that several mechanisms are involved in the uptake of quinine by PMN, including a viability- and energy-independent process possibly related to reversible association of quinine to cell structures (particularly the membrane). Other mechanisms could involve trapping by protonation and/or active PMN transport systems. Thus, most of the quinine taken up by resting PMN is found in the soluble fraction of disrupted cells. This may partly explain the depressive properties of quinine.

Antimetabolites↗
PubMed1990

Production by K 562 cells of an inhibitor of adherence-related functions of human neutrophils.

Certain tumor cells generate factors that inhibit neutrophil chemotaxis. Our study was designed to explore whether such factors are produced by K 562 malignant cells and whether these have a broader effect in altering neutrophil functions. After 48 h of in vitro culture of K 562 cells, the culture medium and the cells were separated, lyophilized, and extracted with ethanol. These K 562 products, i.e., either the cell or supernatant extract, inhibited both nonstimulated locomotion and locomotion induced either by FMLP or activated serum. Furthermore, K 562 products inhibited neutrophil adherence and oxidative burst induced by opsonized zymosan, whereas oxidative burst induced by PMA or FMLP was not altered. K 562 products had an inhibitory effect on the PMN binding to iC3b-coated particles. They did not modify Mo1 expression of resting cells, did not alter the up-regulation of the receptor induced by FMLP but inhibited the FMLP-induced capping of Mo1 Ag. Con A capping was also inhibited. Actin polymerization in FMLP-stimulated PMN, as measured by flow cytometry and phalloidin binding to F-actin, was inhibited by K 562 products. The inhibitory factor present in K 562 products (cell and culture supernatant) was purified in three steps including gel filtration, ion-exchange chromatography, and IEF. The eluted active fraction corresponded to single band of about 8 kDa on SDS-PAGE. From these experiments, it is concluded that K 562 malignant cells in culture contain and release a low molecular mass factor (congruent to 8 kDa) that inhibits all adherence-related functions of neutrophils, whereas it does not alter FMLP- or PMA-induced oxidative burst. Further studies are needed to assess whether products of other tumor cells also act on the neutrophil by inhibiting adherence-related functions, Mo1 function and capping, and actin polymerization.

Actins↗