Plasma and synovial fluid concentration of doxycycline following low-dose, low-frequency administration, and resultant inhibition of matrix metalloproteinase-13 from interleukin-stimulated equine synoviocytes.

The study investigates the effects of low-dose, low-frequency doxycycline administration on synovial fluid concentrations and the resultant inhibition of matrix metalloproteinase-13 (MMP-13) in horses. It concludes that such treatments achieve synovial fluid concentrations that can reduce MMP-13 expression, suggesting the potential use of doxycycline as a disease modifying osteoarthritic drug.

Objective of the Research

The primary aim of this study was to test the effectiveness of low-dose, low-frequency doxycycline administration in achieving protective concentrations within the synovial fluid. This approach was intended to maintain levels below the minimum inhibitory concentration 90 (MIC90), preventing most equine pathogens from proliferating and potentially providing a strategy for managing osteoarthritis.

Research Methodology

• The study deployed a descriptive pharmacokinetic approach with a crossover design involving two groups of six horses.
• Each horse received an oral dose of doxycycline, and the concentrations in their plasma and synovial fluid were measured using high performance liquid chromatography.
• The first group received a dosage of 5 mg/kg of body weight every 24 hours, while the second group received the same dose every 48 hours.
• Samples from the first group were collected over 120 hours and those from the second group over 192 hours.
• Synoviocytes in-vitro were treated with an interleukin-1α stimulant for MMP synthesis, followed by adding synovial fluid to the culture medium for further observation.

Key Findings

• The results demonstrated that mean doxycycline concentration in plasma and synovial fluid, enough to inhibit MMP-13, was achieved faster in the second group.
• Reduced active MMP-13 protein concentration was found in the culture medium where doxycycline was present, indicating an inhibitory effect of the drug on MMP-13 production.
• Additionally, synoviocytes cultured in doxycycline-containing medium exhibited significant decrease in MMP-13 gene expression compared to the controls, further substantiating the inhibitory effect of the drug.

Conclusion

The study found that low-dose, orally administered doxycycline can achieve synovial fluid concentrations in-vivo capable of reducing MMP-13 expression. This suggests significant promise for the potential use of doxycycline as a drug that can modify the course of osteoarthritis. The evidence supports the continued investigation into doxycycline as a treatment option for osteoarthritis in equines.