What Is a Diet Induced Obese Mouse?
A DIO (diet induced obese) mouse is a C57BL/6 - "Black 6" - mouse which has been made obese through conditioning with a special diet. These diets tend to be high in fat, however there are sometimes other modifications made such as added sugar and there are varying types of fat used to create the diet.Advantages of C57BL/6 DIO Mice
- Obese Black 6 mice can be used to effectively model pre-diabetic symptoms and study the progression of metabolic syndrome. The model allows researchers to look at factors that can be controlled at earlier disease stages and study behaviors and compounds that can slow progression of the disease or reverse disease development. Examples include the impact of dietary changes and/or supplements after a period of time on high fat diet (HFD), efficacy of compounds for weight loss, appetite control and the role of exercise in high fat diet fed models.
- DIO mice can provide insights on the influence of high fat diet on a model over time for factors such as food intake, energy expenditure, glucose tolerance, and insulin resistance.
- The DIO mouse model is useful in evaluation of anti-obesity compounds and therapies.
- Mice fed a high fat diet model many of the complications and comorbidities of obesity and metabolic syndrome such as islet cell changes, leptin, corticosterone, adiponectin, adipose depots, nephropathy retinopathy and neuropathy.
- C57BL/6 DIO mice are also used to model nonalcoholic fatty liver disease (NAFLD), with or without streptozotocin (STZ) injections.
Mouse Strains Suitable for High Fat Diet Studies
Strains and stocks of mice respond differently to high fat diets. Outbred mice, such as Swiss Webster, will show a varied response when fed high fat diet, similar to what we expect in a human population. These models are useful for studying a varied population and elucidating the role of genetics in response to high fat diets.Some inbred strains of mice are sensitive and will show marked weight gain when fed a high fat diet, whereas other strains are resistant and demonstrate weight gain similar to mice fed a control diet. Inbred models also show varying characteristics of metabolic syndrome based on genetic background. Taconic recommends using C57BL/6NTac mice as they show a more robust response to high fat diet than other Black 6 mouse strains.
Other Contributing Factors in Responsiveness to High Fat Diets:
- Sex of the mice will influence phenotype. Males and females of different strains will show a varied response when fed a high fat food. For example, some reports indicate that while Black 6 DIO females will demonstrate weight gain similar to males when fed a high fat diet, they will not express increased plasma glucose levels and impaired insulin tolerance.
- Age at which the diet is started can have an impact on overall weight gain and food intake. Most studies indicate that animals should be young adults, generally six to ten weeks of age, when beginning a high fat diet in order to gain the most body weight. This is true even when diet is fed for the same length of time. Starting high fat feeding on older adult mice can be useful for studying the impact of dietary changes in adults.
- Type of diet selected will impact the phenotype of the model. Response to very high fat diet (VHFD) will typically lead to more severe hyperglycemia and hyperinsulinemia, whereas high fat diet (HFD) will lead to a less severe phenotype. Formulations and varied sources of fat content used by different diet manufacturers may also have an impact.
- The health status of an animal has been shown to impact the phenotype of C57BL/6 DIO mice. Some reports indicate that germ-free mice are resistant to diet induced obesity. Data collected by Taconic indicates that weight gain in Murine Pathogen Free™ and Restricted Flora™ mice is similar, and customers have reported that glucose and insulin levels are comparable.
- Housing density has been revealed to impact overall weight gain of HFD fed mice. Group housed mice tend to show more weight variability than mice that are singly housed, most likely due to dominant mice eating more food , but will generally gain more weight more rapidly than singly housed mice. However, there can be variation depending on the model selected.
- Time on diet will influence the characteristics of the DIO mouse model. Mice will generally start to show increased weight gain when compared to controls within 1 week on diet; more severe phenotypic characteristics will take 10-12 weeks or more to develop.
- Other factors such as microbiome, caging type, enrichment and bedding type can all influence the attributes of DIO mice.
Best Practices for Creating a Diet Induced Obese Model
- Mice should be within a three-gram weight span when being placed on diet and should be from a single week of birth.
- Maintaining mice in the same housing groups for the duration of the study is recommended. At Taconic, we house males ten per cage from when they are placed on diet at six weeks of age through twenty-six weeks, which is typically the oldest we have in our colonies.
- Mice should arrive at least one week prior to being placed on high fat diet and acclimated on normal chow for this period. After one week, mice can be converted to high fat diet.
- Approximately one to two weeks after high fat feeding, study animals will show more significant increases in weight compared with control mice.
- High fat diets should be stored in the freezer in order to maximize shelf life.
- High fat food should be placed on the cage floor in order to enable easy access for mice. This food should be changed during weekly cage changes.
- Bedding should not be edible as it will reduce the amount of diet consumed. For the same reason, chew sticks are not recommended for enrichment.
- Housing units such as hiding boxes and tubes tend to increase aggression in Black 6 and most outbred mice and make them territorial. Shredded paper and nestlets seem to be the most useful forms of enrichment for DIO mice.
Typical Characteristics of C57BL/6NTac Mice on D12492 High Fat Diet
- Obvious weight difference by 14 weeks of age, though DIO and controls start to have varied maximum weights one to two weeks after starting diet.
- DIO mice typically begin to exhibit some pre-diabetic symptoms at 12-14 weeks.
- Elevated glucose and pancreatic insulin as well as insulin resistance by 18 weeks of age.
- Elevated leptin, corticosterone by 20 weeks of age.
- Liver complications (steatosis) by 22 weeks of age.
