Uptake and intracellular activity of NM394, a new quinolone, in human polymorphonuclear leukocytes

Intracellular Penetration and Effects of Antibiotics on Staphylococcus aureus Inside Human Neutrophils: A Comprehensive Review

Neutrophils are important assets in defense against invading bacteria like staphylococci. However, (dysfunctioning) neutrophils can also serve as reservoir for pathogens that are able to survive inside the cellular environment. Staphylococcus aureus is a notorious facultative intracellular pathogen. Most vulnerable for neutrophil dysfunction and intracellular infection are immune-deficient patients or, as has recently been described, severely injured patients. These dysfunctional neutrophils can become hide-out spots or “Trojan horses” for S. aureus. This location offers protection to bacteria from most antibiotics and allows transportation of bacteria throughout the body inside moving neutrophils. When neutrophils die, these bacteria are released at different locations. In this review, we therefore focus on the capacity of several groups of antibiotics to enter human neutrophils, kill intracellular S. aureus and affect neutrophil function. We provide an overview of intracellular capacity of available antibiotics to aid in clinical decision making. In conclusion, quinolones, rifamycins and sulfamethoxazole-trimethoprim seem very effective against intracellular S. aureus in human neutrophils. Oxazolidinones, macrolides and lincosamides also exert intracellular antibiotic activity. Despite that the reviewed data are predominantly of in vitro origin, these findings should be taken into account when intracellular infection is suspected, as can be the case in severely injured patients.

Prulifloxacin: clinical studies of a broad-spectrum quinolone agent

Prulifloxacin, the lipophilic prodrug of ulifloxacin, is a new oral fluoroquinolone with a broad spectrum of in vitro activity against various Gram-positive and Gram-negative microorganisms. Currently, it is the most potent in vitro fluoroquinolone against Escherichia coli and Pseudomonas aeruginosa, and also has the lowest potential of inducing the emergence of resistant strains for these bacteria. It exhibits good penetration in target tissues and fluids, and possesses a long half-life, thus allowing for once-daily administration. Prulifloxacin has been successfully tested in Phase III randomized, controlled trials including patients with acute exacerbations of chronic bronchitis, uncomplicated and complicated urinary tract infections, and chronic bacterial prostatitis. Results are awaited from recently completed and ongoing Phase III randomized, placebo-controlled studies testing prulifloxacin for the treatment of traveler's diarrhea. Prulifloxacin has an acceptable toxicity profile, comparable to that of other fluoroquinolones, with gastric disturbances, diarrhea, nausea and skin rash of mild-to-moderate severity being the most frequent adverse events. Additional research is needed to further elucidate the promising role of prulifloxacin in the treatment of infections sustained by multidrug-resistant pathogens and to consolidate the wide spectrum of activity from a clinical standpoint.

Prulifloxacin: a brief review of its potential in the treatment of acute exacerbation of chronic bronchitis

Exacerbations of chronic bronchitis (AECB) are a major cause of morbidity and mortality in patients with chronic obstructive pulmonary disease (COPD), and their impact on public health is increasing. The new fluoroquinolones have an excellent spectrum providing cover for the most important respiratory pathogens, including atypical and “typical” pathogens. Not surprisingly, different guidelines have inserted these agents among the drugs of choice in the empirical therapy of AECB. The pharmacokinetic and dynamic properties of the new fluoroquinolones have a significant impact on their clinical and bacteriological efficacy. They cause a concentration-dependent killing with a sustained post-antibiotic effect. This review discusses the most recent data on the new fluoroquinolone prulifloxacin and critically analyses its activity and safety in the management of AECB.

Prulifloxacin: a new antibacterial fluoroquinolone

In the last few years, the antimicrobial activity, efficacy and relative safety of fluoroquinolones have made them attractive for the treatment of community-acquired and nosocomial infections. Prulifloxacin is a new fluoroquinolone antibacterial agent with a broad spectrum of activity against Gram-positive and -negative bacteria. Prulifloxacin is available for oral use, and after absorption is metabolized in to the active form, ulifloxacin. It exhibits good penetration in target tissues and a long elimination half-life, allowing once-daily administration. A number of randomized, controlled clinical trials carried out in Europe demonstrated the efficacy of prulifloxacin in the treatment of urinary tract (acute uncomplicated and complicated) and respiratory tract infections (acute exacerbations of chronic bronchitis), in comparison with the most widely used drugs such as ciprofloxacin, co-amoxiclav and pefloxacin. Prulifloxacin was generally well tolerated. The most frequent adverse reactions observed in clinical trials were gastric pain, diarrhea, nausea and skin rash. This review focuses on the characteristics of prulifloxacin, summarizing the relevant preclinical and clinical data.

Pharmacologic characteristics of prulifloxacin

Prulifloxacin, the prodrug of ulifloxacin, is a broad-spectrum oral fluoroquinolone antibacterial agent. After absorption, prulifloxacin is metabolized by esterases to ulifloxacin. The drug has a long elimination half-life, allowing once-daily administration. In vitro, ulifloxacin is generally more active than other fluoroquinolones against a variety of clinical isolates of Gram-negative bacteria, including community and nosocomial isolates of Escherichia coli, Klebsiella spp., Proteus, Providencia and Morganella spp., Moraxella catarrhalis, Haemophilus spp., and Pseudomonas aeruginosa. Gram-positive organisms, including methicillin- or oxacillin-susceptible Staphylococcus aureus, Enterococcus spp. and Streptococcus pneumoniae, are susceptible to ulifloxacin. In well-designed clinical trials, prulifloxacin showed good clinical and bacteriological efficacy (similar to that of ciprofloxacin) and was generally well tolerated, demonstrating a similar tolerability profile to that of ciprofloxacin. In conclusion, the in vitro inhibitory and bactericidal activities exhibited by ulifloxacin and the favorable characteristics shown by its prodrug (prulifloxacin) in clinical trials, particularly indicate this drug for the treatment of lung and urinary infections.

Prulifloxacin

Prulifloxacin, the prodrug of ulifloxacin, is a broad-spectrum oral fluoroquinolone antibacterial agent. After absorption, prulifloxacin is metabolised by esterases to ulifloxacin. The drug has a long elimination half-life, allowing once-daily administration. Ulifloxacin is generally more active in vitro than other fluoroquinolones against a variety of clinical isolates of Gram-negative bacteria, including community and nosocomial isolates of Escherichia coli, Klebsiella spp., Proteus, Providencia and Morganella spp., Moraxella catarrhalis and Haemophilus spp. The activity of ulifloxacin against Pseudomonas aeruginosa varies between countries. Gram-positive organisms, including meticillin- or oxacillin-susceptible Staphylococcus aureus, Enterococcus spp. and Italian community isolates of Streptococcus pneumoniae are susceptible to ulifloxacin. Activity against Spanish strains of S. pneumoniae is moderate. In well designed clinical trials, good clinical and bacteriological efficacy (similar to that of ciprofloxacin, amoxicillin/clavulanic acid or pefloxacin) was seen with prulifloxacin 600 mg once daily for 10 days in patients with acute exacerbations of chronic bronchitis or complicated lower urinary tract infections (UTIs), and with single-dose prulifloxacin 600 mg in acute, uncomplicated lower UTIs. Prulifloxacin was generally well tolerated in clinical trials, with a similar tolerability profile to that of ciprofloxacin.

Discrepancy between uptake and intracellular activity of moxifloxacin in a Staphylococcus aureus-human THP-1 monocytic cell model

The correlation between uptake of moxifloxacin by THP-1, a continuous line of monocytic cells devoid of intrinsic bactericidal properties, and its activity against Staphylococcus aureus ATCC 25923, a susceptible reference strain (MIC and minimal bactericidal concentration of moxifloxacin, 0.1 mg/liter), was studied in a 5-h assay. The uptake of the drug, added to the culture medium at 0.2 to 32 mg/liter, was evaluated by high-performance liquid chromatography. The ratio of the cellular to extracellular concentration of moxifloxacin reached, at equilibrium, 4.36 +/- 0.39 in uninfected cells and 6.25 +/- 0.41 in infected cells. The intracellular activity of moxifloxacin, introduced into the extracellular fluid at 0.06 to 8 mg/liter, was determined by the enumeration of viable bacteria. At concentrations < or =0.2 mg/liter, the drug inhibited only the intracellular bacterial growth, while at concentrations > or =0.5 mg/liter, it decreased the bacterial inoculum by less than 1 log(10) unit, with a maximum effect at 3 to 4 h, followed by regrowth of surviving bacteria to 80 to 120% of the original level at 5 h. In contrast, when killing curves were determined by using Mueller-Hinton broth with a similar inoculum (10(7) CFU/ml), moxifloxacin at concentrations > or =0.2 mg/liter reduced the inoculum by at least 3 log(10) units at 3 to 4 h, leaving < or =0.1% survival at 24 h. Persisters exhibited a fluoroquinolone susceptibility identical to that of S. aureus ATCC 25923. Our data indicate that moxifloxacin at therapeutic extracellular concentrations accumulates approximately sixfold in infected THP-1 cells and remains active intracellularly, but significantly less active than under in vitro conditions.

Quinolones alter defense reactions mediated by macrophages

The innate host defense system is regulated in part by the number and activation of the function of neutrophils and macrophages. The immunological effects of a variety of quinolones on host defense functions of macrophage are reported. Ofloxacin (OFLX), lomefloxacin (LFLX), tosufloxacin (TFLX), fleroxacin (FLRX), sparfloxacin (SPFX) and levofloxacin (LVFX) significantly inhibited phagocytosis of Escherichica coli by macrophages. Moreover, TFLX markedly potentiated the expression of the adhesion molecule Mac-1 by macrophages. No significant alteration was detected in the adherence and the expression of adhesion molecule Mac-1 in macrophages treated with the other quinolones. In contrast, OFLX, LFLX, TFLX, and LVFX were effective in significantly increasing the production of hydrogen peroxide, while the other agents did not. These results suggest that the quinolones at a therapeutic concentration differentially affect phagocytosis, adhesion, and the production of hydrogen peroxide by macrophages.

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.

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.

Comparative studies of modulatory effect to the function of rat peritoneal neutrophils treated with new quinolones

Some of the immunological effects of a variety of new quinolones on adhesion, phagocytosis, and production of reactive oxygen intermediators in neutrophils were studied. Ofloxacin, lomefloxacin, fleroxacin, and levofloxacin potentiated the phagocytosis of Escherichia coli in neutrophils. Moreover, lomefloxacin, and sparfloxacin significantly potentiated adhesion of neutrophils. In contrast, tosufloxacin was effective in significantly and persistently potentiating the production of superoxide anion, whereas the other agents markedly inhibited such production. Furthermore, tosufloxacin was effective in significantly potentiating the production of hydrogen peroxide, whereas sparfloxacin markedly inhibited such production. These results suggest that the new quinolones at a therapeutic concentration may affect functions such as phagocytosis, and production of superoxide anion in neutrophils.

Possible interaction between new quinolones and immune functions in macrophages

Some of the immunological effects of a variety of new quinolones on chemotaxis and the production of superoxide anion in rat macrophages were studied. All of the new quinolones examined at a dose range of 0.5 to 50 microg/ml significantly inhibited chemotaxis in a dose-dependent manner in rat macrophages. Moreover, the new quinolones at a dose of 0.5 microg/ml were effective in markedly potentiating the generation of superoxide anion. These results indicate that the new quinolones may modulate immune functions in rat macrophages.

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.