Extra-Label Bisphosphonate Effects on Intra-Articular Inflammation in Juvenile Horses Challenged with Intra-Articular Lipopolysaccharide

Abstract Anecdotal assertions that bisphosphonates, such as clodronate disodium (CD), exhibit anti-inflammatory properties has led to extra-label use, despite a lack of scientific evidence of its efficacy. The objective of this study was to determine the effects of CD on intra-articular inflammation, hypothesizing that intra-muscular administration of CD would reduce intra-articular inflammation following an acute inflammatory challenge by lipopolysaccharide (LPS). To test this, 32 yearling Quarter horses were stratified by age (500 ± 13 d), BW (336 ± 26 kg), sex (n = 16 female; n = 16 male) and initial bone optical density into 4 treatment groups. The 140-d study consisted of two phases: Phase 1 (d 0 to 83) and Phase 2 (d 84 to 140) emulated sale preparation and early performance training, respectively. Horses were housed individually (3.6 m × 7.3 m) and fed to meet requirements of growing horses undergoing moderate training. Treatments consisted of control (CON; n = 8; no CD), single-dose (1X; n = 8; d 84), two-doses (2X; n = 8; d 0, 84), and four-doses (4X; n = 8; d 0, 42, 84, 126) of CD. All horses received iso-volumetric intramuscular injections of 1.8mg/kg BW clodronate disodium (OSPHOS) or saline (placebo) on d 0, 42, 84, and 126. Following treatment administration on d 126, radial carpal joints of each horse were injected with 0.8 mL of either 0.5 ng sterile LPS derived from Escherichia coli O55:B5 or sterile lactated Ringer’s solution as a contralateral control. Synovial fluid was collected before LPS injection (h 0) and at 6, 12, 24, and 336 h post injection. Synovial fluid was analyzed using an ELISA for prostaglandin E2 (PGE2), an indicator of joint inflammation. Data were log transformed and analyzed using the MIXED procedure of SAS. There was an h × LPS interaction (P < 0.01) confirming an acute, transient inflammatory response with increased PGE2 at 6, 12, and 24 h compared with the contralateral control joint, and resolved (P = 0.62) by h 336 post-injection. There was a treatment × h × LPS interaction (P = 0.02) in which 1X, 2X and 4X CD groups had greater synovial PGE2 concentrations at 6 h post-injection in the LPS joint compared with CON. In summary, intra-articular LPS induced localized inflammation, and the PGE2 response was greater in all horses treated with CD. The results of this study reject the hypothesis, suggesting clodronate disodium administration does not reduce intra-articular inflammation following acute induced synovitis.