Investigating the Effect of Enterally Administered Capromorelin on Body Weight in Mice (Mus musculus)

Abstract

Significant weight loss in mice (Mus musculus) is a welfare concern and can alter physiology and behavior in ways that may confound research aims. In this study, factorial design was used to investigate the effect of enterally administered capromorelin on changes in mouse body weight overall and with various research-related interventions, such as administration of analgesics, anesthesia, or surgery. BALB/c mice (n = 61 [27 males/34 females] for analysis) were randomized into 8 intervention-treatment groups with 2 treatment allocations: capromorelin (10 mg/kg) or control, and 4 intervention allocations: no intervention; buprenorphine extended-release (XR) alone; buprenorphine XR, meloxicam, and anesthesia; or surgery under anesthesia with buprenorphine XR, meloxicam, and bupivacaine administered. Mice were habituated to handling, weighing, and voluntary consumption of condensed milk, which was used as the control solution and later a vehicle for capromorelin delivery, for 5 d (days 0 to 4). Then, mice received their interventions followed by 3 days of daily treatment or control administration (days 7 to 9). Body weights were measured daily (days 8 to 11 and day 14) to compare with baseline weights (days 0 to 4 and day 7) and evaluate for treatment and intervention effects on body weight. The interventions resulted in a decrease in group body weights 3 and 4 d after the interventions were conducted. Overall, body weights increased more in mice given capromorelin compared with control, and mice treated with capromorelin returned to, or exceeded, baseline weights faster. The weight loss was mitigated by capromorelin administration in all interventions except for the buprenorphine XR-only group. It is recommended to clinically consider enterally administered capromorelin to mitigate research-induced weight loss in mice.

Keywords: Ethiqa XR, extended-release buprenorphine by Fidelis Animal Health; GhrRA, ghrelin receptor agonists; IGF-1, insulin-like growth factor 1; RoE, return to or exceed [baseline weight]; buprenorphine XR, extended-release buprenorphine.

Figure 1.

Intervention group body weight, in grams, over the baseline period (days 0 to 4 and day 7) by treatment allocation. Boxplots represent the median and IQR, the marker represents the mean, and the range is denoted by the whiskers. There were no statistically significant differences in baseline weight between treatment assignments (P = 0.9386), intervention groups (P = 0.8943), or any intervention-by-treatment group combinations (P = 0.8385).

Figure 2.

Treatment group body weight, in grams, by day from baseline (days 0 to 4 and day 7) and after interventions (days 8 to 14) for all intervention groups combined (groups N-S). Boxplots represent the median and IQR, the marker represents the mean, and the range is denoted by the whiskers. Treatment effect (capromorelin compared with control) was significant (*) on each of the individual days when each day was analyzed separately (P_{day 8} = 0.0070; P_{day 9} < 0.0001; P_{day 10} < 0.0001; P_{day 11} = 0.0128; P_{day 14} = 0.0404) and when analyzed over the postintervention period days 8 to 14 (P < 0.0001). The interventions, regardless of treatment (combined capromorelin and control), resulted in a significant (†) decrease in group weights 3 d (P_{day 10} = 0.0313) and 4 d (P_{day 11} = 0.0157) after interventions but not over the period days 8 to 14 (P = 0.0586).

Figure 3.

Mean percent change in body weight from baseline weight for intervention groups N through S by treatment allocation (capromorelin or control) and for all treatment groups combined (capromorelin and control mice). Groups N^t, I^t, and S^t gained more weight than controls over days 8 to 14 (P_N = 0.0348; P_I = 0.0032; P_S = 0.0020). When each day was analyzed separately, treatment effect was significant (*) for group N days 9 to 10 (P_{day 9} = 0.0116; P_{day 10} = 0.0384), group I days 8 to 10 (P_{day 8} = 0.0423; P_{day 9} = 0.0023; P_{day 10} = 0.0032), and group S days 9 to 11 (P_{day 9} = 0.0088; P_{day 10} = 0.0050; P_{day 11} = 0.0013).

Figure 4.

Kaplan-Meier graph demonstrating the time, in days, to RoE baseline weight for control (solid lines) and capromorelin-treated mice (dashed lines). Inclusive of all interventions, the median time to RoE baseline weight for the treated group was 1 d compared with the untreated (control) group’s median time of 4 d. The median time to RoE baseline weight for group N^t was 1 d compared with 1.5 d for group N^o (P = 0.0253) with 100% N^t compared with 87.5% N^o RoE baseline weight by 7 d postintervention. The median time to RoE baseline weight for group I^t was 1 d compared with 7 d for I^o(P = 0.0015) with 100% I^t compared with 75% I^o animals RoE baseline weight by 7 d postintervention. A comparison between treated and control animals within groups B and S trended toward significance (P_B = 0.0698; P_D = 0.1003).