A non-arthropathic dose and its disposition following repeated oral administration of ofloxacin, a new quinolone antimicrobial agent, to juvenile dogs

Effects of TNFR1 gene silencing on early apoptosis of marbofloxacin-treated chondrocytes from juvenile dogs

Quinolones (QNs)-induced cartilaginous lesions in juvenile animals by chondrocyte apoptosis is an important toxic effect, which results in the restriction of their use in pediatrics. However, limited data about QNs chondrotoxicity are available for evaluation of the potential toxicity in both animals and human cartilage. To explore whether tumor necrosis factor/its receptor (TNF/TNFR1) signaling pathway is involved in the early apoptosis of marbofloxacin-induced chondrocytes, canine juvenile chondrocytes were treated with 0, 20, 50 and 100 μg/mL marbofloxacin. Results showed that the apoptosis rates of the chondrocytes at 2, 8 and 24 h were significantly increased in a concentration- and time-dependent manner (P <  0.05). The mRNA levels of apoptosis-related factors in TNF/TNFR1 signaling pathways and the protein levels of TNFα and TNFR1 were increased in canine chondrocytes treated with 20-100 μg/mL marbofloxacin (P <  0.05) while TNFR1 gene silencing significantly decreased the chondrocyte apoptosis and inhibited the mRNA expression of TNF/TNFR1 downstream signaling molecules after 100 μg/mL marbofloxacin treatment at 8 h (P <  0.01). It was confirmed that activated TNF/TNFR1 signaling pathway may play a leading role in the early apoptosis of marbofloxacin-induced canine juvenile chondrocytes, which is helpful for clinical estimation or prevention of the risk of QNs.

Studies on articular and general toxicity of orally administered ozenoxacin in juvenile rats and dogs

AIM

Ozenoxacin is a nonfluorinated quinolone antibacterial approved for topical treatment of impetigo. Because quinolones have known chondrotoxic effects in juvenile animals, the potential toxicity of ozenoxacin was assessed in preclinical studies.

MATERIALS & METHODS

Ozenoxacin or ofloxacin (300 mg/kg/day for 5 days, for each compound) was orally administered to juvenile rats, and oral ozenoxacin (10-100 mg/kg/day for 14 days) was administered to juvenile dogs.

RESULTS

In juvenile rats, ozenoxacin showed no chondrotoxicity, whereas ofloxacin produced typical quinolone-induced lesions in articular cartilage in three of ten rats. Oral ozenoxacin administration to juvenile dogs showed no chondrotoxicity or toxicologically relevant findings in selected target organs.

CONCLUSION

Ozenoxacin was generally well-tolerated in juvenile rats and dogs, with no evidence of quinolone-induced arthropathy.

Early Pathophysiologic Feature of Arthropathy in Juvenile Dogs Induced by Ofloxacin, a Quinolone Antimicrobial Agent

Arthropathy in dogs induced by ofloxacin, a quinolone antimicrobial agent, was pathophysiologically investigated. In the in vivo studies, ofloxacin was administered orally once or twice at 20 mg/kg/day to male juvenile (3-month-old, n = 3) or adult (36-month-old, n = 2) dogs, and the humeral and femoral heads were examined pathologically. Unlike adult dogs, fluid-filled vesicles were macroscopically observed on the articular surfaces of one juvenile dog 24 hours after a single treatment with ofloxacin. These lesions were seen in all juvenile dogs by twice dosing. Microscopically, fissures or cavity formations in the middle zone of the articular cartilage were noted only in juvenile dogs. Furthermore, the cartilage matrix from the abnormal area to the articular surface showed a decreased safranin-O staining intensity, suggesting proteoglycan depletion. Ultrastructurally, chondrocytes in the middle zone of juvenile dogs displayed dilatation of the cisternae in the rough endoplasmic reticulum as an initial hallmark. In the in vitro studies, chondrocytes isolated from the articular cartilage of naive juvenile dogs were exposed to ofloxacin at 6.3–100 μg/ml for 24 hours. Although no changes were noted in the deoxyribonucleic acid synthesis, protein synthesis, or proteoglycan release at concentrations of up to 100 μg/ml, the proteoglycan synthesis was evidently decreased in a dose-dependent manner from 12.5 μg/ml. The results obtained suggest that the inhibitory action of ofloxacin on proteoglycan syntheses in the chondrocytes may largely contribute to the early morphologic features in the articular cartilage of the juvenile dog.

Effect of oxygen tension on tissue-engineered human nasal septal chondrocytes

Tissue-engineered nasal septal cartilage may provide a source of autologous tissue for repair of craniofacial defects. Although advances have been made in manipulating the chondrocyte culture environment for production of neocartilage, consensus on the best oxygen tension for in vitro growth of tissue-engineered cartilage has not been reached. The objective of this study was to determine whether in vitro oxygen tension influences chondrocyte expansion and redifferentiation. Proliferation of chondrocytes from 12 patients expanded in monolayer under hypoxic (5% or 10%) or normoxic (21%) oxygen tension was compared over 14 days of culture. The highest performing oxygen level was used for further expansion of the monolayer cultures. At confluency, chondrocytes were redifferentiated by encapsulation in alginate beads and cultured for 14 days under hypoxic (5 or 10%) or normoxic (21%) oxygen tension. Biochemical and histological properties were evaluated. Chondrocyte proliferation in monolayer and redifferentiation in alginate beads were supported by all oxygen tensions tested. Chondrocytes in monolayer culture had increased proliferation at normoxic oxygen tension (p = 0.06), as well as greater accumulation of glycosaminoglycan (GAG) during chondrocyte redifferentiation (p < 0.05). Chondrocytes released from beads cultured under all three oxygen levels showed robust accumulation of GAG and type II collagen with a lower degree of type I collagen immunoreactivity. Finally, formation of chondrocyte clusters was associated with decreasing oxygen tension (p < 0.05). Expansion of human septal chondrocytes in monolayer culture was greatest at normoxic oxygen tension. Both normoxic and hypoxic culture of human septal chondrocytes embedded in alginate beads supported robust extracellular matrix deposition. However, GAG accumulation was significantly enhanced under normoxic culture conditions. Chondrocyte cluster formation was associated with hypoxic oxygen tension.

TNF/TNFR₁ pathway and endoplasmic reticulum stress are involved in ofloxacin-induced apoptosis of juvenile canine chondrocytes

BACKGROUND AND PURPOSE

Quinolones cause obvious cartilaginous lesions in juvenile animals by chondrocyte apoptosis, which results in the restriction of their use in pediatric and adolescent patients. Studies showed that chondrocytes can be induced to produce TNFα, and the cisternae of the endoplasmic reticulum in quinolone-treated chondrocytes become dilated. We investigated whether TNF/TNFR₁ pathway and endoplasmic reticulum stress (ERs) are involved in ofloxacin (a typical quinolone)-induced apoptosis of juvenile canine chondrocytes.

EXPERIMENTAL APPROACH

Canine juvenile chondrocytes were treated with ofloxacin. Cell survival and apoptosis rates were determined with MTT method and flow cytometry, respectively. The gene expression levels of the related signaling molecules (TNFα, TNFR₁, TRADD, FADD and caspase-8) in death receptor pathways and main apoptosis-related molecules (calpain, caspase-12, GADD153 and GRP78) in ERs were measured by qRT-PCR. The gene expression of TNFR₁ was suppressed with its siRNA. The protein levels of TNFα, TNFR₁ and caspase-12 were assayed using Western blotting.

KEY RESULTS

The survival rates decreased while apoptosis rates increased after the chondrocytes were treated with ofloxacin. The mRNA levels of the measured apoptosis-related molecules in death receptor pathways and ERs, and the protein levels of TNFα, TNFR₁ and caspase-12 increased after the chondrocytes were exposed to ofloxacin. The downregulated mRNA expressions of TNFR₁, Caspase-8 and TRADD, and the decreased apoptosis rates of the ofloxacin-treated chondrocytes occurred after TNFR₁-siRNA interference.

CONCLUSIONS AND IMPLICATIONS

Ofloxacin-induced chondrocyte apoptosis in a time- and concentration-dependent fashion. TNF/TNFR₁ pathway and ERs are involved in ofloxacin-induced apoptosis of juvenile canine chondrocytes in the early stage.

Age-dependent effects on redox status, oxidative stress, mitochondrial activity and toxicity induced by fluoroquinolones on primary cultures of rabbit tendon cells

The age-related difference in fluoroquinolone-induced tendon toxicity was investigated. In vitro tendon cells from juvenile and young adult rabbits, respectively, were incubated with quinolone (nalidixic acid, NA) or fluoroquinolone (ofloxacin, OFX or pefloxacin, PEF) at 0.01 microM to 1 mM for 72 h. Redox status, glutathione (GSH), reactive oxygen species (ROS), and mitochondrial activity were assessed using intracellular fluorescent probes. Fluorescence signal was detected on living adherent tenocytes in microplates using cold-light cytofluorometry. Tendon toxicity differed significantly between the two cell groups and the difference was greatest with highest dose (1 mM). For 72 h, significant (p < 0.001) differences between immature and young adult primary tenocytes were observed for redox status decrease, GSH decrease, and ROS production increase. Mitochondrial activity remained unaltered in immature tenocytes. We confirm two groups of intrinsic tendon toxicity (OFX/NA vs. PEF) associated to oxidative stress (GSH decrease). Our in vitro experimental model confirms the clinical observations of age dependent tenotoxicity. First group (NA, OFX) showed greater intrinsic tenotoxicity for young adult than immature tenocytes, second group (PEF) was highly toxic for immature and young adult cells. The three quinolones do not altered mitochondrial activity in immature tenocytes whereas alteration was observed in young adult tenocytes.

EXTRAPOLATION OF PRECLINICAL PHARMACOKINETICS AND MOLECULAR FEATURE ANALYSIS OF “DISCOVERY-LIKE” MOLECULES TO PREDICT HUMAN PHARMACOKINETICS

The prediction of human pharmacokinetics from preclinical species is an integral component of drug discovery. Recent studies with a 103-compound dataset suggested that scaling from monkey pharmacokinetic data tended to be the most accurate method for predicting human clearance. Additionally, interrogation of the two-dimensional molecular properties of these molecules produced a set of associations which predict the likely extrapolative outcome (success or failure) of preclinical data to project human pharmacokinetics. However, a limitation of the previous analyses was the relative paucity of data for typical "discovery-like" molecules (molecular weight >300 and/or clogP >3). The objective of this investigation was to generate preclinical data required for extension of this dataset for additional discovery-like molecules and determine whether the aforementioned findings continue to apply for these molecules. In vivo nonrodent intravenous pharmacokinetic data were generated for 13 molecules, and data for 8 additional molecules were obtained from the literature. Additionally, the various scaling methodologies and molecular features analysis were applied to this new dataset to predict human pharmacokinetics. Whereas the predictive accuracies demonstrated across all of the various methodologies were lower for this higher clearance compound dataset, scaling from monkey liver blood flow continued to be an accurate methodology, and human volume of distribution was similarly well predicted regardless of scaling methodology. Lastly, application of the molecular feature associations, particularly data-dependent associations, afforded an improved predictivity compared with the liver blood flow scaling approaches, and provides insight into the extrapolation of high clearance compounds in the preclinical species to human.

Inhibitory effect of several fluoroquinolones on hepatic microsomal cytochrome P-450 1A activities in dogs

We examined inhibitory effects of ofloxacin (OFX), orbifloxacin (OBFX), ciprofloxacin (CFX), enrofloxacin (EFX) and norfloxacin (NFX) on cytochrome P-450 1A (CYP1A) activities using hepatic microsomes from four beagle dogs. Ethoxyresorufin O-de-ethylation was referred as CYP1A activities. All the fluoroquinolones inhibited the reaction in a noncompetitive manner. The determined inhibitory constants were the followings; 10.1 +/- 3.8 mM for OFX, 6.43 +/- 2.01 mM for OBFX, 0.726 +/- 0.134 mM for CFX, 4.06 +/- 1.19 mM for EFX and 4.75 +/- 1.63 mM for NFX respectively. As these values are >100-fold of plasma concentrations after a clinical single dose of the fluoroquinolones, it is suggested that the inhibitory effect on CYP1A activities is not so high to elicit drug-drug interaction with CYP1A substrates, when these fluoroquinolones are co-administered. Mechanism based inhibition was also examined in this study. Of the five fluoroquinolones examined, OFX, OBFX and CFX had this inhibition manner. As this inhibition is irreversible, inhibitory effects of the three fluoroquinolones may accumulate, when they are repeatedly administered. Therefore, OFX, OBFX and CFX may result in substantial drug-drug interaction with a CYP1A substrate even in clinical states. As EFX is metabolized to CFX in the body, it may also have the same possibility.

The effects of oral and intramuscular administration and dose escalation of enrofloxacin on the selection of quinolone resistance among Salmonella and coliforms in pigs

The effect of route of administration and dose of enrofloxacin (Baytril) on the development of fluoroquinolone resistance in Salmonella and Escherichia coli in the intestinal tract of pigs was investigated. Healthy pigs at the age of 8-10 weeks were infected with a mixture of susceptible wild-type (MICciprofloxacin = 0.03 microg/ml) and a mutant Salmonella typhimurium with reduced susceptibility to fluoroquinolones (MICciprofloxacin = 0.5 microg/ml) (in the ratio 99:1) and treated with 2.5 mg/kg bwt enrofloxacin by either intramuscular (i.m.) or oral (p.o.) administration at time points either 4 or 24 h after the infection. The treatment via the intramuscular route of administration (24 h after the infection) was carried out with elevated doses of 7.5 and 15 mg/kg bwt as well. Emergence of resistance during a 3-day treatment period and persistence up to 13 days after treatment, was monitored by counting the resistant and total number of coliforms and Salmonella in faeces of the pigs. High frequencies of fluoroquinolone resistance developed rapidly among the coliform flora independent of route of administration, dose or time of initiation of the treatment. Selection for resistance among the artificially introduced Salmonella was reduced by using the intramuscular route and by escalating the dose 3 or 6 times the recommended dose of 2.5 mg/kg bwt, which also resulted in shortening of the period, in which the pigs were shedding Salmonella. The resistance among the coliform flora persisted for at least 2 weeks. The Salmonella infection was cleared in all cases during the 2 weeks independent of frequency of resistance. The study showed that resistance is very easily selected by treatment with enrofloxacin at the recommended dose 2.5 mg/kg bwt, but also that the intensity of selection can be reduced by using intramuscular dosing (instead of oral dosing) and by escalating that i.m. dose. The results obtained with Salmonella also showed that even very small changes in the active drug concentrations might completely change the intensity of selection.

In Vitro Discrimination of Fluoroquinolones Toxicity on Tendon Cells: Involvement of Oxidative Stress

Tendinopathy are classic side effects observed with fluoroquinolones antibiotics. A previously validated model based on a spontaneously immortalized rabbit tendon cell line (Teno cell line) was used to evaluate cellular responses to the fluoroquinolones pefloxacin (PEF), ofloxacin (OFX), levofloxacin (LVX), and ciprofloxacin (CIP), in various concentrations. Cell viability, redox status changes, reduced glutathione content, and reactive oxygen species production were assessed using neutral red, Alamar blue, monobromobimane and 2,7-dichlorofluorescindiacetate fluorescent probes, respectively. Living adherent tenocytes were analyzed using a cold light cytofluorometer adapted to 96-well microplates. All fluoroquinolones showed moderate cytotoxicity after 24 h and more severe, significant toxicity after 72 h on tendon cells. Moreover, two groups of fluoroquinolones may be differentiated: intrinsic toxicity for tendon cells was high with ciprofloxacin and pefloxacin [redox status decrease was 80 and 62% (*p < 0.05) for PEF and CIP at 1 mM for 72 h, respectively], but moderate with ofloxacin and levofloxacin LVX [redox status decrease was 30 and 22% (*p < 0.05) for OFX and LVX at 1 mM during 72 h, respectively]. Our model supports a role for early oxidative stress in the development of fluoroquinolone-induced tendinopathy. Moreover, our study indicates that intrinsic toxicity to tendon cells varies across fluoroquinolones. The Teno cell line may be a useful model for detecting and evaluating tendon toxicity of new fluoroquinolones and other drugs associated with tendinopathy.