¹BG Klinik Tübingen, Eberhard Karls Universität Tübingen, Tübingen, Deutschland
²Klinisch-Experimentelle Chirurgie, Universität des Saarlandes, Homburg, Deutschland

Text

Objectives and questions: Loop diuretics, such as furosemide, are widely used in cardiovascular diseases and disorders with fluid accumulation. By inhibiting the Na+/K+/2Cl− transport system in the loop of Henle, treatment with furosemide is associated with increased renal calcium excretion as well as higher levels of parathyroid hormone and bone-specific alkaline phosphatase, indicating accelerated bone turnover. Consequently, furosemide treatment has been linked to decreased bone mineral density and an increased risk of hip fractures. However, there is little information on whether furosemide also affects the process of fracture healing.

Material and methods: The effect of furosemide on fracture healing was studied in a stable closed femur fracture model in mice using intramedullary screw fixation. The animals were treated daily with intraperitoneal injections of furosemide (15 mg/kg, n = 19) or vehicle (control, n = 20). Fracture healing was investigated by X-ray, biomechanics, micro-computed tomography (µCT), histology, immunohistochemistry and Western blotting (WB) at 2 and 5 weeks after fracture. Comparison between the two groups was performed using the unpaired Student’s t-test. All data are given as Mean ± SEM. Statistical significance was accepted for p < 0.05.

Results: The biomechanical analysis revealed a significantly reduced bending stiffness in furosemide- treated animals at 2 weeks after fracture when compared to controls (3.1 ± 0.3 vs. 9.6 ± 1.2 N/mm). This was associated with a significantly lower ratio of bone tissue (29.8 ± 2.6 vs. 62.2 ± 5.0%) and a higher ratio of fibrous tissue (52.2 ± 4.0 vs. 30.2 ± 6.1%) within the callus of furosemide-treated animals, indicating impaired fracture healing. Histological analyses revealed a lower number of cathepsin K-positive osteoclasts (1.7 ± 0.2 vs. 3.3 ± 0.4 osteoclasts/high power field), neutrophilic granulocytes and macrophages at 2 weeks after fracture within the callus tissue of furosemide-treated mice. These findings indicate an impaired osteoclast activity and a reduced inflammatory response in furosemide-treated animals when compared to controls. In addition, WB analyses at 2 weeks after fracture revealed a significantly lower expression of NF-κB ligand (RANKL) and the pro-osteogic marker, cysteine-rich angiogenic inducer 61 (Cyr61), within the callus of furosemide-treated animals.

Discussion and conclusions: Taken together, these novel findings demonstrate that furosemide treatment impairs fracture healing by suppressing the activity of osteoclasts and the inflammatory response at an early healing time point. Hence, furosemide shoud be used with caution in patients with a high risk of delayed healing and non-union formation.