Anatomy & Physiology: Current Research
Open Access

Abstract

The Urgent Compelling Need to Swap on a Global Scale from Indirect Mouse Calorimetry (IMC) Towards Direct Mouse Calorimetry (DMC) in Determining the Basal Metabolic Rate (BMR): A Principle of Proof Study

Ginneken VV

Mouse models are important in Biomedical- and Life Sciences. Recently it has been stated that the genetically engineered mouse models for contemporary Obesity and/or Type-2 diabetes (DM2) will in most cases deliver heavily metabolically abnormal animals due to changed gut microbiotics with increased anaerobic CO2 production. Therefore, it can be questioned if indirect calorimetry which it at this moment “the golden standard” in all mouse laboratories over the world, still can be practiced because it is dependent on the conversion factor Respiratory-Quotient (RQ-value: CO2/O2) for expressing energy expenditure into Heat production (HP) in [mW]. Direct calorimetry, however, can accurately quantify HP and thus Basal Metabolic Rate (BMR) in both metabolically normal and abnormal states. In this first manuscript we determined physical properties and characteristics of a former aquatic flow-through twin detection Setaram calorimeter used for measuring Basal Metabolic Rate of fish under adverse environmental conditions (anoxic-, hypoxic-, acid- environmental water). Our objective of this study was to determine if this Setaram calorimetric system with stainless steel vessel of 1 liter could be used in the physical medium air in order to measure energy expenditure in mouse models. This first [Technical note] describes the physical properties and characteristics in the medium water and air of this calorimetric set up. Characteristics of the calorimetric system in air were for the initial baseline over 80 minutes a heat flow of 13.44 ± 1.611 (mW) and for the end baseline over 175 minutes 14.95 ± 1.79 (mW) so the ∆-Baseline (initial –end) was 13.44-14.95 = -1.51 (mW). The drifting baseline over the total experiment of 33h was (14.95 / 13.44) * 100% = 1.1124% with a drifting baseline per hour was 0.035 % per hour which are common values for twin detection Calvin calorimeters. We calculated based on the heat transfer characteristics from water to stainless steel (aquatic calorimeter) in combination with the specific heat capacity of water Cp-water of 4,1884 [kJ K-1] vs Cp-air is 0.001293 [kJ K-1] an aquatic time-constant τwater of 30.48 min vs τair or = 0.019605 min. Because the τair was so small deconvolution techniques (earlier successfully applied in water), correcting for the lag time of the system had no effect. This study also includes the first successful “principle of proof” pilot-experiment with one single mouse locked up for ≈ 14 h proves that measuring the energy expenditure with a single mouse in the 1 liter stainless steel calorimetric vessel in the medium air corresponds to measured values of wild strain mouse used in indirect calorimetry (IMC) (of ≈10 mW/g). A precondition was that in order to prevent suffocating of the mouse in the one liter vessel both vessel (Measurement and Reference: twin detection measurement were supplied with one liter of air per minute- with this former aquatic flow-through twin detection Setaram calorimeter. Although there is in Bio-calorimetry a switch to cell-, (sub)cellular, molecular and biomolecular interactions, this study with “whole animal” calorimetry proves that at the organismal level important fundamental questions are still unanswered and open related to the pathogenesis of human diseases like Obesity and metabolic related disorders like Type-2 Diabetes and more fundamental Life Sciences related processes like ‘ageing’. In addition, also the research area of nutraceuticals can be tested with DMC.