Comparison of methods for determination of animal fat content (body composition analysis)

Comparison of methods for determination of animal fat content

The incidence of obesity is increasing year by year, and there is a tendency to accelerate. Obesity is associated with many chronic diseases such as diabetes, fatty liver, dyslipidemia, hypertension, coronary heart disease, etc. It is one of the diseases that seriously affect people's health and quality of life, and has become a serious public health problem facing all countries in the world. Experts pointed out that obesity, AIDS, drug abuse and alcoholism together constitute a new four major social medical problems. Therefore, it is an urgent task to carry out research on subjects related to obesity.

We have long used experimental animal models (such as mice, rats) to do a lot of research on the etiology of human obesity and the method of treating obesity. The most important point in such research is that we need to find reliable and accurate methods for measuring the body composition of animals. Chemical analysis is the gold standard for measuring body composition. This method requires the animal to be killed, so the animal cannot be measured repeatedly over a long period of time. In addition, the process of the chemical analysis method takes a long time and requires a large amount of work. Therefore, methods of rapid in vivo measurement are critical to measuring body composition that changes over time. There are several methods for determining body composition, such as Dual Energy X-ray Absorptiometry (DXA), Computed Tomography (CT), Magnetic Resonance Imaging (MRI), isotope. The dilution method, Total Body Electrical Conductivity (TOBEC) and Quantitative Magnetic Resonance (QMR) are briefly introduced below for the characteristics of each method.

DXA, CT and MRI are non-invasive, non-destructive methods.

1. Dual energy X-ray absorptiometry

DXA in vivo determination of fat is based on the measurement of bone density using a bone densitometer, expansion and extension for fat content and distribution. The modified device emits a beam of broad wavelengths by an ultra-stable X-ray generator, and the X-rays of the two energies can be obtained by the X-ray beam filtering pulse technique, that is, the weak X-rays of the two energies of high energy and low energy, After the X-ray passes through the examined site, it is accepted by the high and low energy detectors moving synchronously with the X-ray tube. The signal is transmitted to the computer for data processing, and body fat tissue, non-fatty tissue and bone minerals can be calculated. The parameters, bone mineral density and other parameters, the scanning time is about 6 minutes. This method has been widely used in the analysis of body composition of experimental small animals. However, the accuracy of this method of measurement will vary depending on the instrument and the software used.

2. CT and MRI

CT and MRI can analyze body composition at the tissue and organ levels. Two measurements can be used to obtain images of specific fat pads or organs, allowing for further analysis of the amount of fat and the amount of tissue that makes up the muscle. The CT method has been documented for the measurement of body composition in rats and mice, and the analysis of body composition by MRI has also increased. Although both CT and MRI have been successfully used to analyze body composition and obtain information on body fat distribution, measurement and analysis are time consuming and require manipulation by personnel who are familiar with the instrument.

A common disadvantage for the three measurement methods mentioned above (DXA, CT, and MRI) is that all three methods require anesthesia or sedation of the animal. Experimental animals must remain absolutely immobile during the scan. It is well known that anesthesia or sedation will bring about side effects such as reduced food intake, decreased body temperature, and the risk of death.

3. TOBEC

TOBEC is also a fat content measured by an indirect method. The principle is that the adipose tissue is basically non-conductive, and the water and dielectric in the "non-fat tissue" component become a good conductive substance, and the amount of the muscle is measured indirectly by measuring the conductivity, and then the fat amount is calculated. The advantage of the TOBEC method is that it is cheap, the instrument is easy to carry, the accuracy is high, and the operation is simple. However, the value measured by this method is not accurate enough, and the extremely small error of the amount of muscles leads to a large amount of fat error, and it is impossible to The changes were tracked. Isotope dilution and TOBEC measurement methods do not require sedation or anesthesia of experimental animals.

Isotope dilution determines the amount of fat-free tissue by calculating the total amount of water in the whole body, thereby indirectly obtaining the amount of fat. The key to this approach is to assume that approximately 73% of the non-fat tissue is water.

4. QMR

The emergence of quantitative magnetic resonance (QMR) can solve all the problems mentioned above. The method can obtain different T1 and T2 characteristics by measuring different molecular structures and different ¹ H contents of various substances in the living body, and can accurately measure the body composition of living animals without anesthesia. For example, the QMR system EchoMRITM Animal Body Composition Analyzer (Echo Medical Systems, Houston, TX) is available in a variety of models to accurately measure the body composition of fruit flies and humans, and to perform body fat and lean tissue. Analysis of many parameters such as free water and whole body water content. At present, there are more than 300 users in the world and more than 200 articles have been published. It is recognized as the best method for body composition analysis of experimental animals.

The above picture shows the Echo MRI 3in1 system. The three sample bins above the instrument can be used for component analysis of live mice weighing up to 100g, organs up to 10g and samples weighing up to 300mg. The instrument comes with a computer operating system, which is easy to use and allows users to complete independent operations in just one hour of training. The instrument also has a combined system of mice and rats, a 4-in-1 system and about 20 different models for analysis of rats, birds, monkeys, dogs, etc.