Fluorometric measurement of ofloxacin uptake by human polymorphonuclear leukocytes

Fluorometric and high-performance liquid chromatographic measurement of quinolone uptake by human neutrophils

A fluorometric assay, based on the natural fluorescence of the quinolone nucleus, and high-performance liquid chromatography (HPLC) were compared to determine the penetration of six quinolones (norfloxacin, ciprofloxacin, ofloxacin, fleroxacin, lomefloxacin and temafloxacin) into human polymorphonuclear neutrophils (PMN). Intracellular concentrations after 20 min incubation of the cells with 10 and 25 mg/l were three or more times higher than the extracellular ones. There were no statistical differences between the two methods. At lower extracellular concentrations (2 and 5 mg/l) the intracellular levels of all the quinolones tested were undetectable by HPLC. Fluorometry is a useful method for determining the intracellular penetration of quinolones. The usefulness of HPLC, however, is questionable since it requires great volumes of cells and extracellular concentrations much higher than the therapeutic ones.

Ofloxacin. A reappraisal of its antimicrobial activity, pharmacology and therapeutic use

Ofloxacin is a fluoroquinolone whose primary mechanism of action is inhibition of bacterial DNA gyrase. In vitro it has a broad spectrum of activity against aerobic Gram-negative and Gram-positive bacteria, although it is poorly active against anaerobes. Ofloxacin, unlike most other broad spectrum antibacterial drugs, can be administered orally as well as intravenously. Penetration into body tissues and fluids is highly efficient. Clinical trials with orally and intravenously administered ofloxacin have confirmed its potential for use in a wide range of infections, where it has generally proved as effective as standard treatments. Ofloxacin in well tolerated, and in comparison with other available fluoroquinolones is less likely to cause clinically relevant drug interactions. Ofloxacin thus offers a valuable oral treatment (with an option for intravenous administration if necessary) for use in a wide range of clinical infections, but with a particular advantage in more severe or chronic infections when recourse to parenteral broad spectrum agents would normally be required, thereby providing cost savings and additionally allowing outpatient treatment.

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.

Activity of intracellular antibiotics

We have studied the intracellular bioactivity of several antimicrobial agents against two strains of Staphylococcus aureus, a pathogen sequestrated in phagolysosomes, using peripheral blood neutrophils from human volunteers. This was compared to the activity of cell-associated drugs also measured in vitro. Several discrepancies (high cellular association, low bioactivity) were observed (coumermycin, glycopeptides, erythromycin and clindamycin) which can be due to the binding of the drug to a particular cellular organelle, to intracellular metabolization or inactivation, to unfavourable conditions in the phagolysosome (pH drop), or to a toxic effect of the drug on the functions of the neutrophil. Addition of the antibiotic during ingestion was frequently associated with better neutrophil-dependent killing through several potential mechanisms: coingestion of the antibiotic with the inoculum, modification of opsonization, release of activating substances and fragilization of the microorganism to oxygen-dependent or -independent killing mechanisms.

Activity of antibiotics against Staphylococcus aureus within polymorphonuclear neutrophils

The intracellular location of certain strains of Staphylococcus aureus serves as a reservoir of bacteria which is thought to be important in therapy of recurrent infections in humans and in chronic staphylococcal mastitis in dairy cows. This overview summarizes data pertaining to the intracellular survival of Staphylococcus aureus within polymorphonuclear neutrophils (PMNs) both in vitro and in vivo in the face of antibiotic treatment. While compounds such as rifampin, clindamycin, erythromycin, and ciprofloxacin have been shown to be rapidly taken up by PMNs, the ability of antibiotics to concentrate within PMNs did not strictly correlate with their ability to kill intracellular Staphylococcus aureus. Rifampin and ciprofloxacin have been shown to be the most effective intraphagocytic killing agents, while clindamycin and erythromycin were inactive in these in vitro assays. In vivo, in therapy of Staphylococcus aureus arthritis and peritonitis in humans and in certain mouse models rifampin has generally been shown to be more effective than comparator antibiotics. In a staphylococcal subcutaneous abscess model, however, clindamycin was very effective in curing the Staphylococcus aureus abscesses in this system where PMNs were the primary inflammatory cells involved. The intracellular bacterial counts decreased as rapidly as the extracellular bacteria. Rifampin was also effective in the abscess model but ciprofloxacin was ineffective at the highest doses tested. The relevance of in vitro and in vivo models and the importance of PMNs as a reservoir of infection in staphylococcal diseases in humans and the dairy cow are discussed.

Ofloxacin treatment of Chlamydia pneumoniae (strain TWAR) lower respiratory tract infections

PURPOSE

Limited data suggest that tetracycline or erythromycin is the antibiotic of choice for treating Chlamydia pneumoniae infection, but they are not always effective or well tolerated. Because the fluoroquinolone ofloxacin is effective for Chlamydia trachomatis infections, we investigated its role in treating C. pneumoniae infections.

PATIENTS AND METHODS

Eighty-seven patients were enrolled in a randomized trial of antibiotic therapy for acute lower respiratory tract infections. The patients were randomly assigned to oral treatment with either ofloxacin (400 mg twice a day) or erythromycin (400 mg four times a day) for 10 days. Frozen acute and convalescent serologic specimens were tested for TWAR antibody by microimmunofluorescence. Susceptibility testing of C. pneumoniae to ofloxacin was also performed.

RESULTS

Four patients who received ofloxacin were retrospectively identified as having C. pneumoniae pneumonia (two) or bronchitis (two). Within 2 weeks of starting ofloxacin therapy, all were cured or markedly improved. The minimum inhibitory concentrations of ofloxacin for three previously isolated clinical strains of C. pneumoniae were determined to be 1.0 to 2.0 micrograms/mL, well within the achievable serum levels (3 to 5 micrograms/mL) with ofloxacin therapy.

CONCLUSION

Ofloxacin may be an effective alternative antibiotic treatment for C. pneumoniae respiratory infections.

Stimulation of human polymorphonuclear leukocytes potentiates the uptake of diclofenac and the inhibition of chemotaxis

Diclofenac sodium, a non-steroidal anti-inflammatory drug, has been shown to impair the stimulation of human polymorphonuclear leukocytes (PMNs) by chemoattractants. To gain insight into the mechanism of action of this agent, we investigated the uptake of diclofenac by resting and activated PMNs and the effect of the drug on PMN locomotion. During incubation of resting PMNs at 37 degrees in the presence of 78 microM (25 micrograms/mL) diclofenac, drug uptake reached a plateau in less than 2 min. The resulting cellular to extracellular diclofenac concentration ratio (C/E) was 1.01 +/- 0.13 (mean +/- SD). Stimulation of PMNs at 37 degrees but not at 4 degrees with the chemoattractant formyl-methionyl-leucyl-phenylalanine (fMLP) or phorbol myristate acetate (PMA), induced a rise in diclofenac uptake, which was dependent on incubation time and diclofenac and stimulus concentrations. Maximal C/E was 1.83 +/- 0.18 and 4.40 +/- 0.60 (mean +/- SD) for PMNs stimulated with 10 microM fMLP and 0.16 microM PMA, respectively. The diclofenac associated with PMNs was predominantly present in the soluble fraction of disrupted cells. Interestingly, PMNs which were pretreated with diclofenac and stimulated with fMLP, exhibited impaired random and directional locomotion induced by activated serum, as compared to controls, i.e. PMNs treated with diclofenac alone or fMLP alone. Thus, stimulation of PMNs enhances diclofenac uptake and potentiates the drug impairment of chemotactic activity. These findings could explain, in part, the observed anti-inflammatory properties of this compound.

Uptake and intracellular activity of an optically active ofloxacin isomer in human neutrophils and tissue culture cells

The penetration of an optically active ofloxacin isomer [(-)-ofloxacin] into human neutrophils and different tissue culture cells (HEp-2, McCoy, MDCK, and Vero) was studied and compared with that of ofloxacin by a fluorometric assay. The cellular-to-extracellular-concentration ratios (C/E) of (-)-ofloxacin were always higher than 6, significantly greater than those of ofloxacin at extracellular concentrations of 5 and 10 mg/liter. The penetration of (-)-ofloxacin and ofloxacin was doubled when neutrophils were stimulated by phorbol myristate acetate but not affected after ingestion of opsonized Staphylococcus aureus. The C/E ratios of (-)-ofloxacin and ofloxacin for different tissue culture epithelial cells and fibroblasts were lower than those of neutrophils but still higher than 2. Both compounds produced a significant reduction in viable intraphagocytic S. aureus during 3 h of exposure to antimicrobial agents. We conclude that (-)-ofloxacin appears to reach higher intracellular concentrations than ofloxacin, remaining active inside the neutrophils.