Physiological Responses and Adaptation of Brown Adipose Tissue to Chronic Treatment With Beta 3-Adrenergic Receptor Agonists

  • participants needed
  • sponsor
    National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Updated on 3 October 2022
body mass index
insulin resistance
insulin sensitivity
Accepts healthy volunteers



Brown adipose tissue (BAT) is a type of fat in the body. It may prevent weight gain, improve insulin sensitivity, and reduce fatty liver. Researchers want to see if BAT helps the body burn energy.


To learn more about how BAT works to burn energy.


Healthy people ages 18-40 with a body mass index between 18 and 40


Participants will be screened with:

Medical history

Physical exam

Blood, urine, and heart tests

Dietitian interview

Participants will have an overnight baseline visit. This includes:

Repeats of screening tests

Exercise test

Scans. For one scan, a radioactive substance is injected into the arm.

FSIVGIT: An IV is inserted into veins in the right and left arms. Glucose and insulin are injected in one arm. Blood glucose and insulin levels are measured from the other.

Metabolic suite: Participants stay 18 19 hours in a room that measures their metabolic rate. Monitors on the body measure heart rate, movement, and temperature.

Optional fat biopsy: A small piece of tissue is removed with a needle.

Participants will take 2-4 pills daily for 4 weeks. All women will take the drug mirabegron. Men will be randomly get either the drug or a placebo.

All participants will have a visit after 2 weeks of the pills. They will repeat the screening tests.

Participants will have an overnight visit 2 weeks later. They will repeat the baseline tests.

Participants will keep food and medication diaries.

Participants will have a follow-up visit 2 weeks after stopping the pills. This includes heart tests.



Background issues and controversies

More than ever before, there is a rise in the rates of obesity and diabetes. As opposed to white fat which stores excess calories, brown fat - also known as brown adipose tissue or BAT-consumes this energy to generate heat. In settings of increased food consumption and cold-exposure, studies show that human BAT becomes more active, potentially combatting weight gain. Other emerging evidence indicates that human BAT may be an endocrine organ, releasing hormones into the blood and regulating other organs like skeletal muscle, liver, and the insulin-releasing pancreatic beta-cell. However, alongside these promising studies are those people who believe that there is not enough BAT in humans to be functionally relevant, and it contributes little to heat generation or overall health.

Purpose/Rationale of the proposed study

One of the principal reasons for skepticism about the ability to utilize human BAT is that there is not very much compared to smaller animals in which BAT activation has shown such promise. Therefore, a critical step is to develop medicines that can grow BAT in people and evaluate what kind of health benefits can be achieved.

Specific objectives

This study will administer the clinically-available beta3-AR agonist, mirabegron (Myrbetriq , Astellas Pharma). We will determine whether we can increase BAT volume and activity in people after they have taken this medication daily for four weeks. Our current goal is to see if chronic administration of mirabegron leads to an increase in BAT volume and metabolic activity and if it produces health benefits.

Key elements of what is involved

At the beginning of the study, the participants will undergo a series of tests to determine their baseline amounts of BAT, blood sugar status, and levels of specified hormones. The testing will take place over the course of two to three days while an inpatient on the Metabolic Patient Care Unit at the NIH Clinical Center. Depending on the Cohort, participants will then take the medication alone for four weeks or both the medication and placebo for four weeks each, during which time they will continue their standard daily routines. At two weeks after starting placebo or mirabegron, participants will return for one day for the assessment of any interim changes and to validate safety. At the end of each set of four weeks there will be a second set of inpatient testing over two to three days. Participants will be brought back two weeks after finishing the study for a follow-up safety visit, at which time they will receive an ECG and heart rate monitoring.

Primary outcomes

The primary outcome is either the change in BAT metabolic activity as measured by 18FFDG PET/CT or glucose infusion rate as measured by a hyperinsulinemic euglycemic clamp. Secondary endpoints will examine multiple other factors, including body weight, fat mass, glucose tolerance, changes in levels of hormones, and improved liver function.

Condition Polycystic Ovary Syndrome, Healthy Volunteers
Treatment Placebo, mirabegron, B Complex Plus Vitamin C Tablets
Clinical Study IdentifierNCT03049462
SponsorNational Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Last Modified on3 October 2022

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