Effect of ostarine on liver function in adult horses

Ostarine is a selective androgen receptor modulator which has been shown to increase muscle mass in humans while causing minimal androgenic side effects. Although some studies indicate an acceptable safety profile of ostarine, there have been multiple reports of liver damage in people using the drug. Ostarine has also been detected in some racehorses, yet it is currently unclear if ostarine adversely affects horse health, and especially liver function. The objective of this study was therefore to determine if ostarine affects liver function in adult horses, and it was hypothesized that ostarine would alter indicators of liver health and function. Blood was collected from 9 Standardbreds (ages: mean = 17.22 ± 2.5 years; range = 13–21 years) before treatment (baseline), during a 4-week ostarine treatment period (blood collections in treatment wk 2, 3, 4), and once right after conclusion of the treatment period. The duration of the ostarine treatment period was informed by an ostarine rodent study. Four horses were in the treatment group and received intravenous ostarine injections 4 times a week (on nonconsecutive days), while 5 horses were in the control group and received a vehicle control (ethanol) intravenously on treatment days. The liver enzymes aspartate aminotransferase (AST), gamma-glutamyl-transferase (GGT), and glutamate-dehydrogenase (GLDH) were quantified in the horse's blood samples. Data were analyzed by mixed-model ANOVA. For AST, GLDH, and GGT, there was no significant treatment effect (P = 0.37, P = 0.27, P = 0.34, respectively). Significant effects were found for the day of blood sampling, i.e., sampling time point, for AST (P < 0.001), for GLDH (P < 0.001), and for GGT (P < 0.001). These effects of sampling day may be related to the administration of ethanol (the vehicle) to both the treatment and control groups. Based on the liver enzymes monitored in this small study, ostarine does not appear to alter liver function in idle adult horses receiving ostarine for 4 weeks. It is, however, possible that this study was underpowered to detect smaller differences between the groups. Larger future studies should investigate whether ostarine adversely affects other organs or body systems, and whether longer-term or multi-phase administration induces liver damage.