To investigate the ability of doxycycline to modulate collagenases, cytokines, and cytokine receptors in chondrocytes from osteoarthritic (OA) cartilage.
Chondrocytes were isolated from human OA cartilage and treated with doxycycline. Synthesis of collagenases, cytokines, and cytokine receptors was quantified by Northern and Western blot analysis and RNase protection assay.
We observed significant inhibition of matrix metalloproteinases (MMP-1) and MMP-13 mRNA and protein production by chondrocytes, isolated from OA cartilage, after treatment with doxycycline. The decrease in collagenase protein level paralleled a decrease in mRNA for these enzymes, suggesting a transcriptional/posttranscriptional level of control. In addition, treatment with 10 microg/ml doxycycline resulted in 2.2-fold upregulation of transforming growth factor (TGF-beta3) and a significant decrease of interleukin 1alpha (IL-1alpha), IL-1beta, and IL-6 mRNA. Upregulation of TGF-beta RI and TGF-beta RII was also detected. These cytokines are known to affect collagenase expression and could contribute to inhibition of MMP-1 and MMP-13 production by OA chondrocytes. A decrease in IL-1alpha, IL-1beta, and IL-6 would reduce stimulation of MMP production, while an increase in TGF-83 would lead to downregulation of local proinflammatory cytokine production as well as of the collagenases themselves.
Our findings show that a decrease in MMP-1 and MMP-13 collagenase production by articular chondrocytes in response to treatment with doxycycline can be explained by a regulatory effect of doxycycline on the production of cytokine and cytokine receptors.