A. N. Corps, V. A. Curry, R. L. Harrall, D. Dutt, B. L. Hazleman and G. P. Riley

Rheumatology Research Unit, Addenbrooke's Hospital, Cambridge, UK.

Correspondence to: A. N. Corps, Rheumatology Research Unit, Box 194, Unit E6, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK.

Objective. Fluoroquinolone antibiotics such as ciprofloxacin can induce tendon pathology and have various effects on tendon-derived cells in culture. We are investigating whether ciprofloxacin modifies signalling responses in tendon cells.

Methods. Human Achilles tendon-derived cells were preincubated with or without ciprofloxacin (50 µg/ml) and were then challenged with interleukin-1ß (IL-1ß, 1 ng/ml) for up to 48 h. Prostaglandin E₂ (PGE₂) output was assayed by ELISA. The expression of cyclooxygenase-2 (COX-2) was examined by Western blotting.

Results. IL-1ß stimulated a substantial and prolonged increase in the output of PGE₂. Preincubation with ciprofloxacin reduced IL-1ß-induced PGE₂ output at all times tested; the reduction at 48 h was 69% (99% confidence interval 59–79%; 15 experiments). Norfloxacin and ofloxacin also reduced PGE₂ output. However, ciprofloxacin did not affect the induction of COX-2 by IL-1ß, measured at 4 or 48 h.

Conclusions. Ciprofloxacin reduces IL-1ß-induced PGE₂ output in tendon-derived cells. The reduction in PGE₂ output could modulate various cellular activities of IL-1ß, and may be implicated in fluoroquinolone-induced tendinopathy.