10 Extra-label bisphosphonate effects on bone turnover biomarkers in juvenile, exercising horses

Bisphosphonates, such as clodronate disodium (CD), modulate bone metabolism and, though their extra-label use in young horses is common, impacts on skeletal development and longevity are unknown. The objective of the current study was to determine the effects of CD use on systemic biomarkers of bone turnover in juvenile, exercising horses. We hypothesized that bone resorption would decrease, and bone formation would increase as a result of CD administration and repeat treatments would have a greater effect. To test this, 32 juvenile Quarter Horses were used in a 168-d trial. Horses were stratified by age (500 ± 13 d), BW (336 ± 26 kg), sex (n = 16 geldings; n = 16 fillies), and initial bone optical density and randomly allocated to one of 4 treatment groups receiving either 1.8 mg/kg BW CD (OSPHOS®) or isovolumetric saline (placebo). Investigators were blinded to treatments which included a control (CON; n = 8), single-dose CD on d 84 (1X; n = 8), 2-doses CD on d 0 and 84 (2X; n = 8), and 4-doses CD on d 0, 42, 84, and 126 (4X; n = 8). Horses were housed individually in stalls (3.6 × 7.3 m), fed 1% BW/d concentrate, and allowed ad libitum access to Coastal bermudagrass hay and water. Horses exercised 5 d/wk using a free stall exerciser with a phase-based progressive workload; phase I (d 0–84) simulated sales preparation and phase II (d 85–168) mimicked an early training program. Blood was collectedon d 0, 42, 84, 126, and 168, before treatment injections on days of administration. Serum was analyzed for receptor activator of nuclear factor kB ligand (RANKL), tartrate resistant acid phosphatase 5b (TRAP5b), c-terminal crosslinks of type I collagen (CTX-1) and bone-specific alkaline phosphatase (BAP) via commercial ELISA or EIA kits. All data were analyzed using PROC MIXED of SAS with a baseline covariate for BAP and BAP:TRAP5b. No differences were seen in osteoclastic differentiation signal RANKL (P ≥ 0.24). In contrast, a treatment × time interaction was noted for osteoclastic TRAP5b (P = 0.03); specifically, TRAP5b decreased in 4X from d 0 to 126 before returning to baseline at d 168 and decreased in 2X at d 84 compared with baseline, while CON and 1X increased or remained the same over time. Concentrations of CTX-1, a type I collagen degradation marker, increased over time (P < 0.01) in all treatments. Likewise, osteoblastic BAP (P < 0.01) and BAP:TRAP5b (P = 0.04) increased from d 42 to 84 and remained elevated until d 168. These results indicate that m