Effects of methotrexate on the oxidative metabolism of cultured rabbit articular chondrocytes.

OBJECTIVE: The mechanism of action of methotrexate (MTX) in inflammatory joint disease is still unclear. We examined the possible interactions of MTX with the oxidative metabolism of rabbit articular chondrocytes. METHODS: Cell cultures of articular chondrocytes enzymatically isolated from juvenile New Zealand white rabbits were incubated 24 h with either MTX (0.22 or 1.1 microM), bacterial lipopolysaccharide (LPS, 50 microg/ml), or both. Cytofluorometry was then performed using 2',7'-dichlorofluorescein diacetate (DCFH-DA), rhodamine 123 (Rh123), or propidium iodide (PI). These fluorochromes allow evaluation of cellular production of H2O2, mitochondrial membrane potential, and cell viability, respectively. In a separate experiment, we used the Griess colorimetric technique to evaluate cellular nitric oxide (NO) production. RESULTS: Addition of MTX alone (0.22 or 1.1 microM) inhibited spontaneous production by chondrocytes of H2O2 (p < 0.01 and p < 0.001, respectively) and NO (p < 0.01 both concentrations). The LPS induced increase in H2O2, production was inhibited by MTX at 0.22 and 1.1 microM (p < 0.01 both concentrations), whereas the LPS induced increase in NO synthesis was not influenced by MTX, even at 1.1 microM. MTX did not significantly modify mitochondrial activity or cell viability. CONCLUSION: MTX at therapeutic concentrations in vitro inhibits the production of H2O2 and NO by unstimulated chondrocytes, and only the H2O2 overproduction by LPS stimulated chondrocytes. These properties may contribute to the therapeutic effect of MTX in RA.

Nebulized cyclosporine in the rat: assessment of regional lung and extrapulmonary deposition.

BACKGROUND: Nebulized cyclosporine (CsA) has been shown to limit lung allograft rejection as well as intramuscular (IM) CsA, with limited blood diffusion. The present study determined the pharmacokinetic parameters of nebulized CsA, by the assessment of regional lung deposition and extrapulmonary diffusion of CsA. METHODS: CsA was given either by IM injection (10 mg/kg) or by aerosol (at 10 and 25 mg/kg doses); 70 rats were killed at 25 and 50 min, and at 2, 4, 6, 8, 12, 24, or 48 hr after CsA administration. CsA levels were measured in the whole lung, in central and peripheral parts of the lung, in whole blood, kidney, and heart. The areas under the concentration time curves (AUCs) were determined. RESULTS: In blood, kidney, and heart, CsA levels were significantly higher for IM than for aerosol administrations at 10 and 25 mg/kg doses. In the whole lung, the AUC was greater for the aerosol route at 25 mg/kg doses (588 ng x hr/mg) than for the low-dose (200 ng x hr/mg) or IM administration (200 ng x hr/mg). The central to peripheral index of CsA (ratio of AUC central/peripheral part of the lung) was not significantly different for both aerosol administrations (0.63 and 0.69, respectively) and for the IM route (0.81). CONCLUSIONS: Nebulized CsA allows better pulmonary concentration than IM administration, with equivalent central and peripheral deposition whatever the mode of administration, and results in lower levels in blood, kidney, and heart.

Pharmacodynamic activities of ciprofloxacin and sparfloxacin in a murine pneumococcal pneumonia model: relevance for drug efficacy.

We looked for associations between pharmacokinetic (Pk) and pharmacodynamic (Pd) parameters of ciprofloxacin (CPFX) and sparfloxacin (SPFX) and the in vivo efficacy of these antimicrobials in an immunocompetent mouse model of severe Streptococcus pneumoniae pneumonia. Bacterial killing curves recorded in the lungs during the 24 h after single subcutaneous injections of the fluoroquinolones (FQs) in doses ranging from 6.25 to 200 mg/kg were compared with mean Pk/Pd parameters in the serum of the same mice. The impact of the dosing interval on the antimicrobial dose response was evaluated based on the survival of mice treated for 3 days with CPFX (25-200 mg/kg) or SPFX (6.25-50 mg/kg) administered at various intervals from 3 to 24 h. Bacterial killing curves showed that the maximal bacterial decrease achieved in the lungs was correlated, similarly for both FQs, with the area under the curve (AUC) above the minimal inhibitory concentration (MIC) (overall correlation: r = 0.968, P < 10(-4)). CPX attained higher maximal bactericidal effect values, a steeper killing slope and a shorter time to maximal bactericidal effect in comparison with SPX for the highest doses tested. The lower MIC of SPFX compared with CPFX (0.25 vs. 0.75 microgram/ml) and its higher AUC/dose ratio (resulting from a lower serum peak but a longer half-life) translated into a greater area under the bactericidal curve. In the dose fractionation experiments, the Pk/Pd parameter most closely correlated with the survival rate for both FQs was the daily AUC/MIC ratio (r = 0.976, P < 10(-4)). When the AUC/MIC ratio was greater than 160, the probability of a clinical cure was 100%, independently of the dosage schedule.

Use of a new mouse model of Acinetobacter baumannii pneumonia to evaluate the postantibiotic effect of imipenem.

Acinetobacter baumannii is responsible for severe nosocomial pneumonia. To evaluate new therapeutic regimens for infections due to multiresistant strains and to study the pharmacodynamic properties of various antibiotics, we developed an experimental mouse model of acute A. baumannii pneumonia. C3H/HeN mice rendered transiently neutropenic were infected intratracheally with 5 x 10(6) CFU of A. baumannii. The mean log10 CFU/g of lung homogenate (+/- the standard deviation) were 9 +/- 0.9, 9.4 +/- 0.8, 8.6 +/- 1.2, and 7.7 +/- 1.4 on days 1, 2, 3, and 4 postinoculation. The lung pathology was characterized by pneumonitis with edema and a patchy distribution of hemorrhages in the peribronchovascular spaces of both lungs. Abscesses formed on days 3 and 4. Four days after inoculation, subacute pneumonitis characterized by alveolar macrophage proliferation and areas of fibrosis was observed. The cumulative mortality on day 4 was 85%. This new model was used to study the effects of 1, 2, or 3 50-mg/kg doses of imipenem. Imipenem concentrations in lungs were above the MIC for 2 h after the last dose. The in vivo postantibiotic effect (PAE) was determined during the 9-h period following the last dose; it decreased in duration with the number of doses: 9.6, 6.4, and 4 h after 1, 2, and 3 50-mg/kg doses, respectively. In contrast, no in vitro PAE was observed. This model offers a reproducible acute course of A. baumannii pneumonia. The presence of a prolonged in vivo PAE supports the currently recommended dosing intervals of imipenem for the treatment of human infections due to A. baumannii, i.e., 15 mg/kg three times a day.

Efficacy of single-dose ceftriaxone in experimental otitis media induced by penicillin- and cephalosporin-resistant Streptococcus pneumoniae.

We used a gerbil model of otitis media to assess the efficacy of single-dose ceftriaxone against three Streptococcus pneumoniae strains highly resistant to penicillin (MICs, 4 to 8 micrograms/ml) and with various susceptibilities to ceftriaxone (MICs, 0.5, 4, and 8 micrograms/ml). Middle ear infection was induced by bilateral transbullar challenge with 10(7) bacteria per ear. Antibiotic treatment was administered subcutaneously at 2 h postinfection. Infection status was checked 2 days later by counting the bacteria in middle ear and cerebrospinal fluid samples. With the cefriaxone-susceptible strain (MIC, 0.5 microgram/ml), we tested doses of 5 to 100 mg/kg of body weight. With a dose of 50 mg/kg, treatment outcome was equivalent to that with amoxicillin, which was used as a reference (25 mg/kg, two injections); no bacteria were recovered from 82% of the middle ear samples, and the rate of cerebrospinal fluid culture positivity was significantly reduced to 6%, relative to 59% for the untreated controls. Similar efficacy was obtained with a dose of 100 mg/kg against the two ceftriaxone-resistant strains. Pharmacokinetic study indicates that the values of the parameters in plasma after the administration of a dose of 100 mg/kg (peak level of total drug, 268 +/- 33 micrograms/ml; elimination half-life, 0.8 h; area under concentration-time curve, 488 micrograms.h.ml-1) were still suboptimal compared with the values of the parameters measured in pediatric patients after intravenous or intramuscular administration of a dose of 50 mg/kg. Our results indicate the efficacy of ceftriaxone against experimental cephalosporin-resistant pneumococcal otitis and provide a basis for the clinical use of single-dose ceftriaxone against pneumococcal otitis media.

Effect of subinhibitory concentrations of antimicrobial agents on adherence to silicone and hydrophobicity of coagulase-negative staphylococci.

OBJECTIVES: To study the effect of 0.25 MIC of antimicrobial agents on adherence to silicone and hydrophobicity of a slime-producing Staphylococcus epidermidis (ATCC 35984) and non-slime-producing Staphylococcus hominis (ATCC 35982). METHODS: Adherence was assessed in vitro, using silicone rubber immersed in a suspension of bacteria, pretreated with 0.25 MIC of oxacillin, ceftriaxone, vancomycin or pefloxacin. After a 24-h period, adherent bacteria, detached by trypsin and sonication, were counted. Hydrophobicity was assessed by measuring the affinity of pretreated bacteria to p-xylene. RESULTS: For slime-producing S. epidermidis, adherence was significantly decreased by 81%, 91% and 77% with oxacillin, vancomycin and pefloxacin respectively. For non-slime-producing S. hominis, adherence was significantly decreased by 75% and 94% with oxacillin and ceftriaxone respectively. Hydrophobicity of both strains was significantly decreased with oxacillin only. CONCLUSIONS: Adherence of coagulase-negative staphylococci onto silicone can be modified by sub-MICs of some of the antimicrobial agents tested. This effect was different in the slime-producing and non-slime-producing strains, and was not correlated with the mechanism of the inhibitory effect of these antimicrobial agents, or the modification of hydrophobicity. This suggests that some surface components, not involved in hydrophobicity, could play a role in in vitro adherence to silicone.

Mycobacterium avium complex infection in mice: lack of exacerbation after LP-BM5 murine leukemia virus infection.

The murine leukemia virus LP-BM5 has been used to reproduce the model of murine AIDS in order to evaluate the course of infection with the MO-1 strain of Mycobacterium avium complex (MAC). LP-BM5 was inoculated in C57BL/6 mice by intravenous (i.v.) injection either 8 weeks before an i.v. challenge with 10(3) or 10(6) CFU of MAC (coinfection 1) or 10 days after an i.v. challenge with 10(3) CFU of MAC (coinfection 2). During coinfection 2 experiments, the phenotypic alterations in blood lymphocyte subsets were analyzed. During coinfection 1, LP-BM5 infection tended to decrease the mycobacterial growth, with the difference reaching statistical significance for the lower inoculum (10(3) CFU of MAC) (P<0.001). During coinfection 2, LP-BM5 did not exacerbate MAC infection except in the spleen, at day 90 after LP-BM5 challenge (P<0.001). LP-BM5 infection and the LP-BM5-MAC coinfection increased the numbers of activated CD4+ lymphocytes (CD4+ Ly6AE+) (P<0.001), activated CD8+ lymphocytes (CD8+ Ly6AE+) (P<0.001), and activated B lymphocytes (Ly5+ Ly6AE+) (P<0.001). This activation of T lymphocytes could explain the lack of exacerbation of MAC infection and even the trend to a lower level of MAC infection. Thus, this model of retroviral infection of mice does not seem to be a reliable model of immunodepression for the study of MAC infection and its treatments.

[Effects of chloroquine on the replication of a murine retrovirus]. / Effets de la chloroquine sur la réplication d'un rétrovirus murin.

The wide use of chloroquine (Cq) for prophylaxis and chemotherapy of malaria in Africa, and the increased spread of AIDS in areas of this continent where malaria is endemic, raised the question of a possible interaction between chloroquine intake and HIV infection. Indeed, hydroxychloroquine and chloroquine itself have been shown to inhibit HIV-1 replication in vitro, hydroxychloroquine being proposed as a potential useful adjunctive therapy in the treatment of HIV-1 infection. On the other hand, chloroquine has been reported to enhance the replication of Semliki forest and encephalomyocarditis viruses in a mouse model. In an attempt to elucidate Cq effect on retroviral replication, we have studied the effect of various concentrations of chloroquine in vitro (0.1 nmol/l to 25 mumol/l) on Friend retrovirus (FV)-infected fibroblasts of mice and in vivo (2 to 30 mg/kg) on FV-infected mice. No reduction in the number of virus foci was found in chloroquine-treated fibroblasts cultures. In chloroquine treated-infected mice, no differences were observed in the spleen weights, except an increase at 10 mg/kg. A decrease in splenocyte virus titer was only observed at 10 and 30 mg/kg. No differences in the median survival time was observed up to 30 mg/kg. The authors concluded that chloroquine seemed to have variable effects on viral replication in vivo depending on the dosage, but has no influence on the course of FV-induced disease.

Lack of correlation between hydrogen peroxide production and nitric oxide production by cultured rabbit articular chondrocytes treated with fluoroquinolone antimicrobial agents.

The arthrotoxicity of fluoroquinolone antibacterial agents so far remains unexplained. Recent experimental data have indicated an early stimulation of the oxidative metabolism within articular chondrocytes. An in vitro model was designed to analyse the production of oxygen-derived reactive species and glutathione by immature rabbit articular chondrocytes, and the influence of different fluoroquinolones on this model was examined. Primary cultures of chondrocytes were exposed to pefloxacin, ofloxacin or ciprofloxacin at 10 mug/ml, for 24 or 48 hr. Flow cytometric analysis used the vital tracer 2',7'-dichlorofluorescein diacetate (DCFH-DA) and evaluated the production of H(2)O(2) and NO by chondrocytes. Separately, NO production and intracellular glutathione levels were evaluated, with the Greiss colorimetric technique and the Tietze method, respectively. With each fluoroquinolone tested, intracellular levels of the fluorescent compound dichlorofluorescein (oxidized form of DCFH-DA) were significantly higher in treated chondrocytes than in control cells. No significant modification of NO or of glutathione cellular levels was noted. Fluoroquinolones stimulate H(2)O(2) production in immature articular chondrocytes, but have no apparent effect on either NO or glutathione production, at least in the early stages of the chondrotoxicity.

Nebulized cyclosporine for prevention of acute pulmonary allograft rejection in the rat: pharmacokinetic and histologic study.

BACKGROUND: With regard to limiting the systemic effects of cyclosporine A and obtaining better control of acute pulmonary allograft rejection, local immunosuppressive therapy with aerosolized cyclosporine A seems of interest. Given the in situ immunologic mechanisms of acute rejection, as well as the anatomic structure of the lung, this therapy is feasible as previously described by others. The aim of our study is to determine the pharmacokinetic parameters of nebulized cyclosporine A and the best modalities of administration. METHODS: In a pharmacokinetic study, the cyclosporine A was given either by intramuscular injection (10 mg/kg) or by aerosol at 10 and 25 mg/kg doses; 70 rats were killed at 25 and 50 minutes and 2, 4, 6, 8, 12, 24, or 48 hours after cyclosporine A administration. Cyclosporine A levels were measured in whole blood and in the lung. The areas under the concentration time curves were determined. Twenty-four lung transplantations were then performed. The rats were killed on postoperative day 9. Acute rejection was scored on a scale of 0 to 4, and cyclosporine A trough levels were measured in the lung and in the blood. RESULTS: With a jet nebulizer, the mass median aerodynamic diameter was 2.5 microns, with a standard geometric deviation of 2.3. In blood, the area under the concentration curve was greater for intramuscular (80.6 ng.hr/ml) than for aerosol administrations at 10 (15.1 ng.hr/ml) and 25 mg/kg (41.0 ng.hr/ml) doses. In the lungs, the area under the concentration curve was greater for the aerosol route at 25 mg/kg doses (588 ng.hr/mg) than for the low-dose (200 ng.hr/mg) or intramuscular administration (200 ng.hr/mg). The lung targeting index of cyclosporine A (ratio area under the concentration curve-lungs/area under the concentration curve-blood) was greater for both aerosol administrations than for the intramuscular route. In the study of the prevention of acute rejection, rats without immunosuppression (n = 6), rats receiving daily doses of cyclosporine A intramuscularly (10 mg/kg), and rats with aerosolized cyclosporine A daily (10 and 25 mg/kg/day) showed mean grades of acute rejection of, respectively, 4, 2.03 +/- 0.27, 2.33 +/- 0.52, and 2.17 +/- 0.46. The deposition of nebulized cyclosporine A was lower in transplanted than in native lung. CONCLUSIONS: Nebulized cyclosporine A allows better pulmonary concentration than intramuscular administration, and results in lower systemic levels. Prevention of acute rejection is as good with aerosolized cyclosporine A as with intramuscular cyclosporine A. This first pharmacokinetic study of nebulized cyclosporine A could lead to clinical applications.

Systemic prophylaxis of experimental staphylococcal endophthalmitis: comparative efficacy of sparfloxacin, pefloxacin, imipenem, vancomycin, and amikacin.

The preventive efficacy of several antibiotics in experimental staphylococcal endophthalmitis was evaluated. Two hours before bilateral intravitreal infection with 500 cfu of Staphylococcus aureus, 18 pigmented phakic rabbits were assigned to receive a single intramuscular injection of sparfloxacin (50 mg/kg), pefloxacin (50 mg/kg), imipenem (50 mg/kg), vancomycin (30 mg/kg), amikacin (15 mg/kg), or saline and were killed 24 h after infection (6 eyes/group). Sparfloxacin, pefloxacin, and imipenem were significantly (P < .001) more effective than saline. All but 1 of the sparfloxacin-treated eyes were culture negative. To determine whether the effect persisted, an additional 24 rabbits were treated with sparfloxacin, pefloxacin, imipenem, or saline and were killed 48 h after infection (12 eyes/group). Sparfloxacin, pefloxacin, and imipenem were effective (P < .001). All sparfloxacin-treated eyes remained culture negative. These results show that systemic antibiotic administration prevents the development of experimental endophthalmitis and that further studies of sparfloxacin as a prophylactic agent are warranted.

Evaluation of high-dose regimen of paromomycin against cryptosporidiosis in the dexamethasone-treated rat model.

In the dexamethasone-treated rat model of cryptosporidiosis, paromomycin was effective at a dosage of 50 mg/kg/day or more for ileal infection and 200 mg/kg/day or more for cecal infection. At 1 and 3 weeks after treatment, a persistent infection was demonstrated in all rats. These results confirm the anticryptosporidial activity of paromomycin and underscore the limitations of this compound because of its potential toxicity at such high dosages and its inability to eradicate the infection.

[The particular case of azalides: antibiotic diapedesis. Experimental data from a murine model of pneumococcal pneumonia]. / Le cas particulier des azalides: l'antibiodiapédèse. Données expérimentales à partir d'un modèle murin de pneumonie à pneumocoque.

The relations between the clinical efficacy, phagocytic transport phenomena, tissular and sera kinetics have been assessed in a pneumonia murine model. At first, the correlation between the clinical efficacy and pharmacokinetics characteristics has been studied for the erythromycin, spiramycin, roxithromycin, clarithromycin and azithromycin. An in vivo clinical efficacy hierarchy has been established (azi > ery > roxi = azi > spira). A hierarchy identical to the clinical efficacy, has been recognised for the pulmonary elimination half lives and the pulmonar AUC. These could be considered as predictive of these antibiotics activity in the respiratory infections. In a second time, the tissular pharmacokinetics of the azithromycin in leukopenic mice allowed to confirm the leukocytes role in the transport and release of this antibiotic in the midst of the infections site. Finally, this antibiotic demonstrated its efficacy in a bacterienic infection even when administered at a low dosage thus allowing to have sera concentrations identical to those obtained in human clinical case and close to MIC's for S. pneumoniae. The pharmacokinetic novelty displayed by its strong tissular penetration can explain its remarkable efficacy.

Tolerability, kinetics, and efficacy of subconjunctival pefloxacin in pigmented rabbits.

Pefloxacin has been shown to have good intraocular penetration when given systemically. In order to extend its clinical use, we have assessed the tolerability, kinetics, and efficacy of subconjunctival pefloxacin in phakic pigmented rabbits. The tolerability of a single subconjunctival injection of pefloxacin (0.8, 1.6, 8, or 16 mg in 0.2 ml) in the right eyes of eight rabbits was evaluated by clinical and histopathological examination. The 0.8-mg dose of pefloxacin was well tolerated. The kinetics was evaluated after a single subconjunctival injection of 0.8 mg in 18 rabbits. Animals were sacrificed at 1, 3, 5, 7, 12, or 18 h postinjection. Drug concentrations were measured by high-performance liquid chromatography. Pefloxacin was found in the cornea (maximum concentration, 18.13 micrograms/ml; half-life, 3.92 h) and in the aqueous humor (maximum concentration, 3.40 micrograms/ml; half-life, 2.14 h). Pefloxacin did not penetrate into the vitreous humor by this route. The efficacy was evaluated in an experimental model of staphylococcal corneal ulcers in eight rabbits which received two subconjunctival injections of 0.8 mg of pefloxacin at 16 and 24 h after intrastromal inoculation. The results (expressed as mean log10 CFU per milliliter +/- standard deviation) showed that pefloxacin significantly (P < 0.001) reduced the bacterial counts (4.39 +/- 0.97) compared with those in control eyes (6.46 +/- 0.69). For phakic eyes, subconjunctival pefloxacin might be of value for the treatment of corneal ulcers. Further studies are required to determine its penetration into the vitreous humor of aphakic eyes.

Activities of roxithromycin against Mycobacterium avium infections in human macrophages and C57BL/6 mice.

The activity of roxithromycin against three clinical isolates of Mycobacterium avium was compared with that of clarithromycin both in a model of infection of human monocyte-derived macrophages and in a model of established infection of C57BL/6 mice. In the cell culture model, roxithromycin and clarithromycin were bactericidal for strains MO-1 and N-92159 and bacteriostatic for strain N-93043. For the three strains, the differences between the intracellular activities of roxithromycin and clarithromycin were not singificant after 7 days of treatment. Mice were infected with the MO-1 strain. Drugs were given by gavage at a dosage of 200 mg/kg of body weight 6 days per week for 16 weeks starting 5 weeks after infection. At the end of treatment, clarithromycin was more effective than roxithromycin in lungs; roxithromycin was as effective as clarithromycin in spleens. Thus, the activity of roxithromycin was comparable to that of clarithromycin both in vitro and in vivo.

Use of normal C57BL/6 mice with established Mycobacterium avium infections as an alternative model for evaluation of antibiotic activity.

Several murine models have been used to evaluate the activities of antimicrobial agents against Mycobacterium avium infection. The main model used is the beige mouse model, but beige mice are expensive and not easily available. Thus, we developed a model of infection in wild C57BL/6 mice. The drugs that exhibited some activity in a previous model of early infection were evaluated in a new model of established infection. Sparfloxacin (50 mg/kg of body weight), ethambutol (50 mg/kg), minocycline (25 mg/kg), and the inhibitor of the cortisol receptors RU-40555 (100 mg/kg) were compared with clarithromycin (50 mg/kg). Treatments were started 5 weeks after the inoculation and were continued for 21 days. Sparfloxacin and RU-40555, which exhibited a moderate activity in the model of early infection, were not effective in this model of established infection. Clarithromycin and combinations with clarithromycin kept their activities against M. avium infection, both in the spleen and in lungs. The present model of established infection of normal C57BL/6 mice is more relevant than the model of early infection for a stringent evaluation of drugs.

Effects of fluoroquinolones on cultured articular chondrocytes flow cytometric analysis of free radical production.

Using flow cytometry, we previously established in an ex vivo model that fluoroquinolones induce a stimulation of the oxidative metabolism in immature chondrocytes. To assess these findings in an in vitro model, primary cultures of immature articular chondrocytes were incubated with four quinolone solutions: ofloxacin, ciprofloxacin, nalidixic acid at 10 micrograms/ml for 24 hr and pefloxacin at 1, 10 and 100 micrograms/ml for various periods of time (2, 4, 6, 12, 24 and 48 hr). Three fluorochromes were used: DCFH-DA, reflecting cellular production of H2O2, rhodamine 123 (Rh123) and 10-N-nonyl-acridine orange (NAO), which are specific for mitochondrial activity and mass, respectively. In immature chondrocyte cultures treated with pefloxacin, ofloxacin and nalidixic acid at 10 micrograms/ml for 24 hr, levels of cellular fluorescent dichlorofluorescein DCF (oxidized form of DCFH-DA) were significantly higher than in control cells. No significant increase could be registered with ciprofloxacin. In the same experimental conditions, incorporation of Rh123 and NAO was not significantly modified. Pefloxacin (10 micrograms/ml, 24 hr) did not induce any significant increase of DCFH-DA processing either in mature chondrocytes or in alveolar macrophages removed from immature rabbits. Quinolones induce in vitro an early stimulation of the oxidative metabolism in immature but not in mature chondrocytes, a phenomenon that could explain juvenile onset of quinolone arthropathy. This in vitro model could be proposed as an easy and reproducible method for screening potential arthrotoxicity of antimicrobial agents, capable of stimulating the formation of H2O2.