Refining mouse glucose homeostasis assessments
Lead Research Organisation:
UNIVERSITY OF EXETER
Department Name: Institute of Biomed & Clinical Science
Abstract
Mice are often used in research into new treatments for diabetes. This project will improve the tests that we perform in mice used for diabetes research by making them more like those used in human medicine. The new method we propose will also improve animal welfare as the mice need less handling, which can be stressful for them.
Diabetes is a common often life-long condition which occurs when the processes for controlling the amount of sugar (glucose) in our blood stop working properly. Glucose is an important fuel source for our body. Our bodies need to carefully control the amount of glucose in our blood so all our cells and organs have enough energy to work normally, but too much blood glucose can also be harmful. The process of balancing the amount of sugar in our blood is called glucose homeostasis and is controlled cooperatively by organs in our bodies communicating. This involves producing chemical messengers called hormones. Hormones are produced in one type of organ, such as the liver, and the information is received by another organ, such as the brain, which responds appropriately.
Because diabetes is so common and has serious health consequences, we need to do more research to understand what causes it and how we can treat it. There are already some diabetes treatments available, such as giving the hormone insulin, but sometimes these treatments have bad side effects or don't work well in some groups of people. Because diabetes is a disease of the whole body, we need to study it in living animals to truly understand it. Mice are often used for this as they have the same hormones and processes for regulating their blood glucose as people, and have been used for research in this area for over fifty-years.
When doctors think a person might have diabetes, they often perform a test called a glucose tolerance test. In this test a person drinks a very sweet drink containing lots of sugar, to rapidly increase their blood glucose levels. After a period of time, they then have a blood test to measure how much glucose is still in their blood. During this test, if a person's blood glucose regulatory systems are working properly, their body activates processes to bring their blood glucose levels down. If these are not working properly, their blood glucose levels will remain higher for longer; this indicates that they might have or be at risk of developing diabetes. A very similar glucose tolerance test is also used in mice during diabetes research, except that their blood glucose levels are increased by giving them an injection or by using a tube to put the glucose straight into their stomachs. While these approaches are effective, they are not ideal for two reasons. Firstly, unlike when this test is done in people, the glucose does not pass through the mouth of the mice. Because we know that the mouth is an important, yet underappreciated, first stage step in glucose sensing by the body this means that the test in the mouse is not completely comparable to the human test. Secondly, both methods of giving glucose involve picking the mouse up, which can be stressful. We always want to minimise stress in mice for their welfare, but also because it can change their blood glucose levels which can impact the test results.
This project will test a new method of giving mice glucose during the glucose tolerance test, which is adapted from a technique established by a group of scientists in Europe. Because mice like sweet things, you can train them to voluntarily drink glucose from a small tube when offered. This already works for giving drugs to mice in research studies and we want to adapt it for use in glucose tolerance testing. Once we achieve this, we will compare this new method with the old approaches to confirm that it is as effective and less stressful for the mice. We have already talked to other leading scientists across the world, and they are excited to work with us and to start using this new approach.
Diabetes is a common often life-long condition which occurs when the processes for controlling the amount of sugar (glucose) in our blood stop working properly. Glucose is an important fuel source for our body. Our bodies need to carefully control the amount of glucose in our blood so all our cells and organs have enough energy to work normally, but too much blood glucose can also be harmful. The process of balancing the amount of sugar in our blood is called glucose homeostasis and is controlled cooperatively by organs in our bodies communicating. This involves producing chemical messengers called hormones. Hormones are produced in one type of organ, such as the liver, and the information is received by another organ, such as the brain, which responds appropriately.
Because diabetes is so common and has serious health consequences, we need to do more research to understand what causes it and how we can treat it. There are already some diabetes treatments available, such as giving the hormone insulin, but sometimes these treatments have bad side effects or don't work well in some groups of people. Because diabetes is a disease of the whole body, we need to study it in living animals to truly understand it. Mice are often used for this as they have the same hormones and processes for regulating their blood glucose as people, and have been used for research in this area for over fifty-years.
When doctors think a person might have diabetes, they often perform a test called a glucose tolerance test. In this test a person drinks a very sweet drink containing lots of sugar, to rapidly increase their blood glucose levels. After a period of time, they then have a blood test to measure how much glucose is still in their blood. During this test, if a person's blood glucose regulatory systems are working properly, their body activates processes to bring their blood glucose levels down. If these are not working properly, their blood glucose levels will remain higher for longer; this indicates that they might have or be at risk of developing diabetes. A very similar glucose tolerance test is also used in mice during diabetes research, except that their blood glucose levels are increased by giving them an injection or by using a tube to put the glucose straight into their stomachs. While these approaches are effective, they are not ideal for two reasons. Firstly, unlike when this test is done in people, the glucose does not pass through the mouth of the mice. Because we know that the mouth is an important, yet underappreciated, first stage step in glucose sensing by the body this means that the test in the mouse is not completely comparable to the human test. Secondly, both methods of giving glucose involve picking the mouse up, which can be stressful. We always want to minimise stress in mice for their welfare, but also because it can change their blood glucose levels which can impact the test results.
This project will test a new method of giving mice glucose during the glucose tolerance test, which is adapted from a technique established by a group of scientists in Europe. Because mice like sweet things, you can train them to voluntarily drink glucose from a small tube when offered. This already works for giving drugs to mice in research studies and we want to adapt it for use in glucose tolerance testing. Once we achieve this, we will compare this new method with the old approaches to confirm that it is as effective and less stressful for the mice. We have already talked to other leading scientists across the world, and they are excited to work with us and to start using this new approach.
Technical Summary
An oral glucose tolerance test (oGTT) is routinely used clinically for diagnosis of pre-diabetes, gestational diabetes, and resistance to insulin, one of the main pancreatic hormones regulating blood glucose. A GTT measures the ability of a person (or animal) to clear excess glucose from their blood, in a specified period, after a large bolus treatment. GTTs are commonly used worldwide in rodent metabolic phenotyping (in 2021 alone used in at least 258 publications [estimated 8,256 mice]). Oral gavage (gavage oGTT) and (more commonly) intraperitoneal injection (ipGTT) are used to administer the glucose bolus in the mouse GTT. Although less frequently used, the former is the more physiologically relevant as it fully integrates the gastrointestinal tract, including key post-prandial hormone release. However, oral gavage is also not without its limitations: gavaging glucose straight into the stomach bypasses potentially critical early glucose-sensing via the mouth.
This project will refine mouse glucose tolerance testing through validation and dissemination of a simple non-invasive oral micropipette-guided drug administration (MDA) glucose dosing protocol to replace oral gavage in the GTT. MDA-glucose administration will refine the oGTT test in several important ways: 1) providing a more accurate model of human clinical GTT assessments; 2) improved physiological relevance of the assay by accounting for the contribution of oral glucose sensing; 3) minimising handling of animals which will reduce stress, a major confounding variable in glucose homeostasis assessment; and 4) introducing a more user-friendly less invasive oral delivery method which requires no specialist equipment and will be easier to adopt in laboratories compared to the oral gavage. Collaborations with world-leading scientists in the field involved in setting standards and training are already established to enable fast replication, adoption, and dissemination of this refinement.
This project will refine mouse glucose tolerance testing through validation and dissemination of a simple non-invasive oral micropipette-guided drug administration (MDA) glucose dosing protocol to replace oral gavage in the GTT. MDA-glucose administration will refine the oGTT test in several important ways: 1) providing a more accurate model of human clinical GTT assessments; 2) improved physiological relevance of the assay by accounting for the contribution of oral glucose sensing; 3) minimising handling of animals which will reduce stress, a major confounding variable in glucose homeostasis assessment; and 4) introducing a more user-friendly less invasive oral delivery method which requires no specialist equipment and will be easier to adopt in laboratories compared to the oral gavage. Collaborations with world-leading scientists in the field involved in setting standards and training are already established to enable fast replication, adoption, and dissemination of this refinement.
