Synergy between RU 28965 (roxithromycin) and human neutrophils for bactericidal activity in vitro

The utility of spiramycin for preventing transplacental transmission of toxoplasmosis and the efficacy of conventional macrolides against Toxoplasma gondii are subjects of active debate. An in vitro microassay was developed to determine the relative inhibitory activity against T. gondii of 24 conventional macrolides derived from erythromycin and tylosin (14-and 16-membered macrolides, respectively). Macrolides and T. gondii RH tachyzoites were added to monolayers of BT cells grown in 96-well plates. Plates were incubated for 20 h at 37°C, and the growth of T. gondii was then measured by the selective incorporation of [3H]uracil in trichloroacetic acid-precipitable material during an additional incubation of 20 h. Dose-response curves and 50 and 90% inhibitory concentrations (IC50 and IC90, respectively) were determined for each drug. Microscopic examination was performed on stained replicates of the infected monolayers, and the relative toxicities of the drugs for host cells were determined. Spiramycin and tylosin showed only limited activity against T. gondii (IC50 of 20.16 and 20.00 ,ug/ml, respectively). Erythromycin and azithromycin had a better anti-Toxoplasma activity with IC50 of 14.38 and 8.61 ,Ig/ml, respectively, whereas drugs like desmycosin, dirithromycin, and roxithromycin had no detectable activity. Although many macrolides inhibited intracellular proliferation of T. gondii, azithromycin was the only macrolide demonstrating prolonged inhibitory activity on the replication of intracellular tachyzoites. We conclude that conventional 14-and 16-membered macrolides often interfere with the growth of, but may not kill, T. gondii RH tachyzoites in vitro.

mentioning

confidence: 99%

Comparative activity of macrolides against Toxoplasma gondii demonstrating utility of an in vitro microassay

Chamberland

Kirst

Current

1991

“…The excellent penetration of macrolides into and their accumulation within phagocytes (20) may be responsible for their increased activity in this tissue culture system. The macrolide roxithromycin, apart from being bactericidal, has also been observed to enhance the phagocytic functions of polymorphonuclear leukocytes (28). Clarithromycin has been recently shown to be active against M. leprae in vivo in mice, which is attributed to its relatively better pharmacokinetics in mice (9).…”

Section: Resultsmentioning

confidence: 99%

In vitro effects of antimicrobial agents on Mycobacterium leprae in mouse peritoneal macrophages

Ramasesh

Krahenbuhl

Hastings

1989

Mycobacterium leprae synthesizes large quantities of a specific phthiocerol-containing phenolic glycolipid in vivo. We had shown earlier that viable M. leprae readily incorporates radiolabeled palmitic acid into phenolic glycolipid I when residing in cultured macrophages in vitro and that this process is inhibited by the antileprosy drug rifampin. In the present paper we report the application of this observation to the rapid evaluation of over 25 antimicrobial agents for potential antileprosy activity in vitro. All the known antileprosy drugs rifampin, dapsone, clofazimine, and ethionamide inhibited phenolic glycolipid I synthesis. Rifabutin, a spiropiperidyl derivative of rifamycin, also reported to be active in the mouse model, was very effective. Interestingly, the macrolides erythromycin, clarithromycin, and roxithromycin were also found to be active in this system, while D-cycloserine and other cell wall synthesis inhibitors showed no effect. Many of the compounds found to be active in this system have been reported to be effective in vivo in mice. This correlation lends support to the feasibility of using phenolic glycolipid I synthesis for the rapid evaluation of new drugs against leprosy.The increased emergence of drug-resistant strains of Mycobacterium leprae in recent years has emphasized the need to identify new compounds effective in the treatment of leprosy. Since M. leprae does not multiply in vitro, conventional microbiological assays cannot be used for primary evaluations of new drugs for antileprosy activity. Prior to 1960, antileprosy drugs were selected primarily on the basis of empirical results of clinical trials with leprosy patients. The mouse footpad technique developed in 1960 by Shepard (38) proved to be an invaluable tool in the primary selection of new drugs by facilitating comparison of the bactericidal potency of different compounds and by making it possible to differentiate bactericidal activity from bacteriostatic effects. The activity of a drug in the mouse model is strongly correlated with its ultimate efficacy in humans. However, primary evaluation of new drugs by this approach has severe practical limitations since the assay is time-consuming (requires 4 to 8 months) and laborious, requires at least 4 to 5 g of a test compound for a test screening, and is heavily dependent on the compound's having favorable pharmacokinetics in the mouse. The development of a rapid and reliable in vitro drug-screening system would allow primary screening and selection of more compounds with potential antileprosy activity, the activity of which could then be tested in mice prior to clinical trials.A number of in vitro metabolic assay systems have been reported in recent years, and these have been extensively reviewed (22,47,48). These assays are based on the observation that M. leprae, although incapable of proliferation in vitro, retains many of its metabolic functions for a limited period of time outside the host either in tissue culture or in cell-free systems. The metabolism of the organism...

“…The immunosuppressive properties of macrolides have also been implicated as a potential mechanism facilitating bacterial superinfection (23). However, there are no reported cases of macrolide-induced superinfection, even after long-term administration of erythromycin A derivatives (14), and synergy with the bactericidal functions of PMN has been observed in vitro (4,5,20). The ketolide telithromycin has been shown to inhibit PMN oxidant-generating capacity (30).…”

Section: Discussionmentioning

confidence: 99%

“…However, macrolide administration clearly does not result in impaired bacterial eradication in vivo. Synergy between some macrolides and PMN for bacterial killing has even been suggested (4,5,20). HMR 3647 (telithromycin) belongs to a new class of semisynthetic erythromycin A derivatives, the ketolides, characterized by a 3-keto group in place of the L-cladinose moiety at position C-3 of the lactone ring (10).…”

mentioning

confidence: 99%

Effect of Telithromycin (HMR 3647) on Polymorphonuclear Neutrophil Killing ofStaphylococcus aureusin Comparison with Roxithromycin

Vazifeh

Abdelghaffar

Labro

2002

HMR 3647 (telithromycin), a new ketolide, is active on intracellular pathogens. It was previously demonstrated that it inhibits superoxide anion production in a time-and concentration-dependent manner, at concentrations which inhibit 50% of the control response of about 55 g/ml (5 min) to 30 g/ml (30 min); these values are similar to those obtained with roxithromycin, a classical erythromycin A derivative. Here we investigated whether these drugs modified the bactericidal activity of human polymorphonuclear neutrophils (PMN) on four strains of Staphylococcus aureus with different profiles of susceptibility to macrolides and ketolides. We found that the main factor involved in killing was the antibacterial potency of the drugs, although combinations of antibiotics with PMN were slightly more active than each component used alone against two of the four strains. In addition, high concentrations of the drugs, which impaired the PMN oxidative burst, did not impair PMN bactericidal activity. Likewise, some cytokines which enhance PMN oxidative metabolism did not modify PMN bactericidal activity in the presence or absence of macrolides or ketolides. These data suggest that oxygen-independent mechanisms contribute to the bactericidal activity of PMN on these strains of S. aureus. Both live and/or heat-killed bacteria impaired the uptake of telithromycin and roxithromycin (but not that of levofloxacin, a quinolone) in a concentration-dependent manner, owing to a modulation of PMN transductional systems involved in the activation of the macrolide carrier.Polymorphonuclear neutrophils (PMN) are cornerstones of host defenses against bacterial infection. A major mechanism by which these cells destroy pathogens is the production of reactive oxygen species in the phagocytic vacuole after the activation of a complex enzymatic system, the membrane NADPH oxidase (8). It has been observed that erythromycin A-derived macrolides significantly impair oxidant generation by PMN (1,2,3,19). However, macrolide administration clearly does not result in impaired bacterial eradication in vivo. Synergy between some macrolides and PMN for bacterial killing has even been suggested (4,5,20). HMR 3647 (telithromycin) belongs to a new class of semisynthetic erythromycin A derivatives, the ketolides, characterized by a 3-keto group in place of the L-cladinose moiety at position C-3 of the lactone ring (10). HMR 3647 was one of the most active compounds on respiratory pathogens in a series of 11,12-cyclo-disubstituted ketolides synthesized by Roussel-Uclaf (11). In addition, HMR 3647 is active against intracellular microorganisms (e.g., Chlamydia pneumoniae, Legionella pneumophila, Rickettsia spp., and Toxoplasma gondii) (6,9,25,26). It accumulates to significantly higher levels than roxithromycin and also inhibits oxidant production (30). Here we examined whether telithromycin modified the bactericidal activity of PMN on four strains of Staphylococcus aureus with different patterns of susceptibility to macrolides and ketolides. Roxithromycin was ...