Morphologic and biochemical characterization of difloxacin-induced arthropathy in immature beagle dogs

John Eric Burkhardt, Purdue University

Abstract

Quinolones are efficacious antibacterial drugs, but their use is contraindicated in children and growing animals because they have caused arthralgia in the former and arthritic lesions in the latter. The studies reported in this thesis were undertaken to characterize the morphologic and biochemical changes caused in articular-epiphyseal cartilage complexes (AECC) of 3-month-old Beagle dogs by the oral administration of difloxacin, a fluoroquinolone, at 300 mg/kg body weight. Additional studies evaluated the effects of difloxacin on the metabolism of AECC slices in organ culture. In dogs dosed orally with difloxacin, lesions, which were fluid-filled blisters that projected above the contour of the articular surface, developed within certain weight-bearing sites on the humeral and femoral heads. Microscopically, lesions were fissures within the intermediate zone of the AECC, that were lined by necrotic chondrocytes and fragmented extracellular matrix. Ultrastructurally, swelling of mitochondria, which was observed in chondrocytes within 24 hours after treatment with difloxacin, increased temporally and was accompanied by vacuolation of cytoplasm. Ultrastructural changes in extracellular matrix, which included aggregation of glycosaminoglycans (GAG) and clumping of collagen fibrils, were observed only after chondrocytes had undergone necrosis. Biochemically, only collagen was lost from cartilage during the 48 hours following treatment. It was, therefore, interpreted that chondrocytes were primarily affected by difloxacin and that, secondarily, there were rapidly developing changes in the extracellular matrix that were probably caused by enzymatic destruction. In organ cultures of AECC, difloxacin reduced the rates of synthesis of GAG and collagen at concentrations of the drug which were at or above that estimated for the plasma of dogs in the in vivo studies, but their rates of catabolism were not altered. Synthesis of total protein was reduced only by the highest concentration of difloxacin. Ultrastructural changes were not observed in the matrix, but cisternae of rough endoplasmic reticulum of chondrocytes exposed to difloxacin were distended by secretory material. The overall interpretation was that difloxacin affected chondrocytes by interfering with the secretion of GAG and collagen and, that, compressive forces prevented these chondrocytes from surviving in vivo.

Degree

Ph.D.

Advisors

Hill, Purdue University.

Subject Area

Veterinary services|Pathology

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