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Effects of enrofloxacin and magnesium deficiency on matrix metabolism in equine articular cartilage

Celia L. M. DavenportDepartment of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.

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Raymond C. BostonDepartment of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.

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Dean W. RichardsonDepartment of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.

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Abstract

Objective—To investigate the effects of enrofloxacin and magnesium deficiency on explants of equine articular cartilage.

Sample Population—Articular cartilage explants and cultured chondrocytes obtained from adult and neonatal horses.

Procedure—Full-thickness explants and cultured chondrocytes were incubated in complete or magnesium- deficient media containing enrofloxacin at concentrations of 0, 1, 5, 25, 100, and 500 µg/ml. Incorporation and release of sulfate 35S over 24 hours were used to assess glycosaminoglycan (GAG) synthesis and degradation. An assay that measured binding of dimethylmethylene blue dye was used to compare total GAG content between groups. Northern blots of RNA from cultured chondrocytes were probed with equine cDNA of aggrecan, type-II collagen, biglycan, decorin, link protein, matrix metalloproteinases 1, 3, and 13, and tissue inhibitor of metalloproteinase 1.

Results—A dose-dependent suppression of 35S incorporation was observed. In cartilage of neonates, 35S incorporation was substantially decreased at enrofloxacin concentrations of 25 mg/ml. In cartilage of adult horses, 35S incorporation was decreased only at enrofloxacin concentrations of ≥ 100 µg/ml. Magnesium deficiency caused suppression of 35S incorporation. Enrofloxacin or magnesium deficiency did not affect GAG degradation or endogenous GAG content. Specific effects of enrofloxacin on steadystate mRNA for the various genes were not observed.

Conclusion and Clinical Relevance—Enrofloxacin may have a detrimental effect on cartilage metabolism in horses, especially in neonates. (Am J Vet Res 2001;62:160–166)

Abstract

Objective—To investigate the effects of enrofloxacin and magnesium deficiency on explants of equine articular cartilage.

Sample Population—Articular cartilage explants and cultured chondrocytes obtained from adult and neonatal horses.

Procedure—Full-thickness explants and cultured chondrocytes were incubated in complete or magnesium- deficient media containing enrofloxacin at concentrations of 0, 1, 5, 25, 100, and 500 µg/ml. Incorporation and release of sulfate 35S over 24 hours were used to assess glycosaminoglycan (GAG) synthesis and degradation. An assay that measured binding of dimethylmethylene blue dye was used to compare total GAG content between groups. Northern blots of RNA from cultured chondrocytes were probed with equine cDNA of aggrecan, type-II collagen, biglycan, decorin, link protein, matrix metalloproteinases 1, 3, and 13, and tissue inhibitor of metalloproteinase 1.

Results—A dose-dependent suppression of 35S incorporation was observed. In cartilage of neonates, 35S incorporation was substantially decreased at enrofloxacin concentrations of 25 mg/ml. In cartilage of adult horses, 35S incorporation was decreased only at enrofloxacin concentrations of ≥ 100 µg/ml. Magnesium deficiency caused suppression of 35S incorporation. Enrofloxacin or magnesium deficiency did not affect GAG degradation or endogenous GAG content. Specific effects of enrofloxacin on steadystate mRNA for the various genes were not observed.

Conclusion and Clinical Relevance—Enrofloxacin may have a detrimental effect on cartilage metabolism in horses, especially in neonates. (Am J Vet Res 2001;62:160–166)