Boston Area Metabolic Physiology and Energy Balance Core

Overview

The Boston Area Metabolic Physiology Core provides consulting and teaching, use of DEXA scanner for determination of body fat and/or bone density, and use of Coulter Counter to measure cell number and cell size distribution.

Services

Our Core is designed to teach and/or perform for users the following assays

In vivo studies in mice

• Continuous glucose monitoring
• Body composition: DEXA analysis of body fat, lean mass, and bone density
• Body composition: MRI analysis of body fat or lean mass, and water mass
• Energy expenditure measurement by indirect calorimetry
• Food and water intake
• Wireless monitoring of body temperature or heart rate
• Energy content in diet or feces by bomb calorimetry
• Thermal imaging studies

In vitro studies

• Isolation of adipocytes – counting the number and cell size distribution of adipocytes using our new coulter counter equipped with a multisizer (number and size of cells are determined on the same sample at the same time)
• Isolation of adipocyte explants
• In vitro differentiation of pre-adipocytes into adipocytes
• Glucose transport and metabolism studies in isolated adipocytes. Insulin dose response (glucose transport, glucose utilization, lipolysis)
• Lipolysis stimulation and inhibition
• Lactate production, triglyceride synthesis, glucose oxidation in adipocytes

Equipment

Body composition analysis: DEXA and EchoMRI

Noninvasive studies of body composition allow for longitudinal assessment of changes in adiposity as well as regional assessment of adiposity. Other methods for assessment of body composition such as ethanolic KOH hydrolysis of the carcass do not allow for longitudinal assessment and preclude doing other studies in the same rodent at the same time point. With the DEXA scanner and EchoMRI, it is possible to measure metabolic parameters serially to acquire longitudinal measurements. These measurements allow for assessment of body composition in the same animals before and after a dietary or treatment intervention. An investigator can determine, for example, whether alterations in insulin sensitivity precede or follow the development of altered adiposity.

DEXA scanner (GE PIXImus Mouse Densitometer) can measure total body fat mass, lean mass, and also fat content of the abdominal region specifically. The chief advantage of the DEXA scanner over the EchoMRI is the Measurement of bone mineral density (BMD). BMD measurement is collected simultaneously with measurement of body composition. The main disadvantage of the DEXA is that animals must be anesthetized for several minutes during imaging. The core also maintains an isoflurane vaporizer which is kept alongside the DEXA scanner

EchoMRI (EchoMRI 3-in-1 MRI for mice, Echo Medical Systems) can measure total body fat mass, lean mass, and water mass in mice up to 100g in mass. The advantages of the EchoMRI are a faster measurement time (under 2 minutes) and the animals do not require sedation for the procedure. The disadvantage of this machine is that it is larger and not as portable as the DEXA. Our core has two EchoMRI devices, one maintained in the specific pathogen free barrier facility, and one which is kept in the laboratory for terminal measurements. With this setup, investigators can bring their mice to BIDMC to a designated location outside our barrier animal facility and use the EchoMRI. This makes body composition analysis available to investigators who house their mice at other institutions. A second limitation to the EchoMRI is that studies in which mice have metallic implants (e.g., glucose probes or temperature probes) cannot be scanned. Body composition of these animals would instead be measured by DEXA.

Coulter Counter equipped with multisizer This is one of the most heavily used apparatuses by Center members. The Coulter counter has a multisizer which allows measurement of the complete distribution of cell sizes in a fat pad. Most in vitro adipocyte studies need to be expressed per cell so measurement of cell number is necessary to interpret adipocyte glucose transport, glucose and fatty acid oxidation, lipolysis, glucose metabolism and adipocyte secretion studies. In addition, adipocyte size has an impact on cellular metabolism. Therefore, measuring adipocyte size in a given model assists with interpretation of the results of ex vivo metabolic and signaling assays.

CLAMS Indirect Calorimeter A 16 cage Comprehensive Lab Animal Monitoring System (CLAMS) with environmental controls, which allows for powerful research and discovery, particularly in common metabolic disorders that include obesity, type 2 diabetes and non-alcoholic fatty liver disease. A CLAMS is utilized for indirect calorimetry of unrestrained, conscious mice, yielding quantitative measurements of oxygen consumption (VO2), carbon dioxide production (VCO2), respiratory exchange ratio – an indicator of substrate utilization – total energy expenditure, and body temperature. It also provides measures of basal locomotor activity and exercise tolerance, as well as caloric intake. Our CLAMS is specialized, allowing for the precise control of ambient temperature ranging from thermoneutrality (30°C) to cold (4°C). This feature is essential for the systematic quantification of thermogenesis, the capacity to generate body heat from stored energy. Mechanisms that control thermogenesis hold great promise as targets for the treatment of obesity and diabetes, but are poorly understood. The use of a CLAMS in our studies has revealed profound changes in energy substrate utilization and induction of thermogenesis in multiple mouse models. Our CLAMS facility allows for study of 16 mice at a time allowing for multiple simultaneous experiments.

Sable Systems Promethion Indirect Calorimeter (24 cages) is a state-of-the art system allowing high-throughput data collection, noninvasive monitoring of animal weight, and because of an improved cage design, it can be coupled with the DSI continuous glucose monitoring probe and receiver system. The DSI glucose system is not compatible with our existing Columbus Instruments CLAMS. The Promethion’s higher data density allows readings of each mouse every two minutes and provides for greater behavioral, temporal, and energetic information to be collected from a given experiment, reduces the number of animals needed to study, and accelerates the pace of research. The Promethion Core System includes gas analyzers for oxygen, carbon dioxide, and water vapor; sensors to monitor food, water intake, and body weight; 3-dimensional movement measurement (breaks across infrared laser beams); enclosures to control the temperature of the cages, and mouse cages. This system also includes a set of airtight isolation cages where all air in and out of the cages is passed through HEPA filters. These can be used for measurement of mice that are germ-free or have defined microbiota. Isolation cages would also permit the study of diabetes or obesity and infectious agents including COVID-19. The Promethion can read telemetry from either Starr scientific temperature probes or DSI HD-XG probes

The Bomb Calorimeter (Parr Instrument Company) allows for the quantitation of energy content of either food or of feces. Direct calorimetry can measure the caloric value of novel or experimental diets. When coupled with measurements of food intake and indirect calorimetry, a complete picture of energy intake, energy absorption, and energy expenditure can be quickly determined.

Infrared thermography using a thermal camera (FLIR) will help to quantitate heat lost due to differences in vasodilation and vasoconstriction. Thermography has helped to visualize differences in brown fat thermogenesis.

DSI Continuous Glucose Monitoring System includes 24 HD-XG mouse-sized wireless probe that are surgically implanted and will read out glucose and body temperature levels every second for every mouse for 4-6 weeks. These are the only mouse sized telemetry probes commercially available. The system also includes 24 RPC-1 receivers which are placed under the mouse cage and will wirelessly read the glucose telemetry data. The receivers can either be operated as stand-alone devices or simultaneously with the Promethion indirect calorimeter to obtain food and metabolic rate data simultaneously. One used, probes can be refurbished by the manufacturer with additional glucose oxidase enzyme and replacement batteries.The Promethion and DSI systems work simultaneously to record complementary data from the same animal to give unprecedented detail into mouse metabolism (e.g. how neuronal activation by optogenetic stimulation acutely affects glucose homeostasis).

Body Temperature Telemetry system (Starr Scientific) for continuous measurement of core body temperature or heart rate at regular intervals over periods of days to weeks. This requires the implantation of a transmitter into the peritoneal cavity of the animals. Measurements can be collected while animals are in the indirect calorimeter, or in their home cage.

Scintillation counter (The Beckman LS6500 multipurpose scintillation counter provides highly accurate automated counting of 3H and 14C isotopes utilized by the core. The counter is maintained by the BIDMC Division of Endocrinology.