Quantifying energy expenditure in Göttingen Minipigs with the 13C-bicarbonate method under basal and drug-treated conditions

Abstract

Effective treatments of obesity focusing on energy expenditure (EE) are needed. To evaluate future EE-modulating drug candidates, appropriate animal models and methods to assess EE are needed. This study aimed to evaluate the stable isotope 13C-bicarbonate method (13C-BM) for estimating EE in Göttingen minipigs under basal and drug-treated conditions. Four experiments (Expt.1-4) were conducted to assess: 1) the 13C-BM reproducibility using breath sample collection (n=8), on two consecutive days, 2) the effect of two dose levels (5 and 10mg/kg body weight (BW)) of the mitochondrial uncoupler dinitrophenol (DNP) in a crossover design (n=8), 3) sampling method agreement; blood vs. exhaled air (n=6) and 4) 13C-BM using constant isotope infusion compared with indirect calorimetry (IC) (n=3). Results correlated significantly (p<0.001) between days (Expt.1), with an average coefficient of variance of 5.4±2.3%. Administration of 10mg DNP/kg BW increased (p<0.01) EE by 33.2±6.4% (Expt.2). Results based on different sampling methods correlated significantly (p<0.001) and EE increased after 10mg DNP/kg BW (p<0.05) in Expt.3. However, results based on blood sampling were significantly higher (p<0.01) than those of exhaled air. No effect of DNP and significantly different EE results (p<0.05) was observed in a limited number of animals, when constant isotope infusion and blood sampling was compared with IC (Expt.4). In conclusion, the 13C-BM is useful for investigating treatment effects on EE in minipigs. However, further validation under standardized conditions is needed to provide accurate estimates of the 13C recovery factor and respiratory quotient, both of decisive importance when using the 13C-BM.