Circadian Brown Adipose Tissue Metabolism

A Pilot Study to Investigate Circadian Variations in Brown Adipose Tissue Metabolism in Healthy Volunteers.

Brown adipose tissue is poorly understood fat that can metabolize glucose in order to generate heat. Since activated brown fat has a high metabolic rate, it is of great interest as a potential target to combat obesity. However, the signaling and control of brown fat metabolism is poorly understood. Because brown fat uses glucose as its energy source, brown fat metabolism can be imaged with PET/CT using the positron emitting glucose analog F-18 FDG. We have recently shown in mice a striking circadian variation in brown fat metabolism as evidenced by changes in FDG uptake. In this study we endeavor to generate pilot data on a potential circadian variation in brown fat activation in healthy humans.

Study Overview

• Status: Completed
• Conditions: Healthy
• Intervention / Treatment: Device: FDG PET/CT

Detailed Description

Brown adipose tissue is a form of fat that is able to metabolize glucose in order to generate heat. When active, it can convert a great deal of glucose into thermal energy. Activation of brown fat could potentially help to combat obesity by increasing the basal metabolic rate. However, activation and signaling of brown fat is poorly understood. In a mouse model, we have recently shown that there is significant circadian variation in brown fat activation and have also discovered the gene that is responsible for the circadian changes (Gerhart-Hines et al, Nature 2013). Specifically, we have shown that in wild type mice, brown fat activation is high at night and low during the day. Whether human brown fat activation has a circadian component is currently unknown. Showing that brown fat activation in humans is subject to similar circadian rhythms as in mice would be an important step in understanding the signaling of activation and may help to elucidate potential strategies to control activation. Positron emission tomography/computed tomography (PET/CT) is a hybrid imaging modality that allows imaging positron emitting isotopes such as fluorine-18 (F-18) along with anatomic imaging using x-rays. The physiologic information from the PET component is co-registered with the anatomic information from the CT component, permitting accurate localization and quantification of physiologic processes. The most common clinically used positron emitting radiopharmaceutical is F-18 fluorodeoxyglucose (FDG). It is a glucose analog which is taken up by glucose transporters and phosphorylated to FDG-6P by hexokinase. However, isomerase, the next enzyme in the glycolytic pathway, is inactive on FDG-6P and so it is largely trapped in the cell. Therefore, FDG PET/CT gives a map of relative amount of glucose uptake and phosphorylation over the interval from injection to scan. Activated brown fat has robust FDG uptake with very intense signal seen. Therefore, FDG PET/CT can be used both to determine whether a person has activated brown fat at the time of the scan as well as to quantify the overall level of metabolism in the fat. Our primary objective is to gather pilot data on the potential presence of circadian variations in brown fat uptake in young, healthy, lean male volunteers. We plan to do this by performing two FDG PET/CT scans 12 hours apart while the patient remains in a temperature and diet controlled environment leading up to both scans. Our primary hypothesis is that brown fat activity will be higher during the day than at night (as human and mouse circadian rhythms are reversed). We will also pair measurement of cortisol with the FDG injections as cortisol levels provide valuable independent information on the circadian rhythm.

• Study Type: Interventional
• Enrollment (Actual): 10
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United States
  • Pennsylvania
    • Philadelphia, Pennsylvania, United States, 19104
      • University of Pennsylvania

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 45 years (Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: Male

Description

Inclusion Criteria:

• At least 18 years of age and less than 45 years of age
• Able and willing to provide informed consent
• Male gender
• Capable of complying with study procedures and able to lie still in the PET/CT scanner for up to 40 minutes continuously
• Normal fasting glucose (less than 100 mg/dl)
• No evidence of significant concurrent illness
• Follow typical sleep/wake cycle of generally asleep at night and awake during the day

Exclusion Criteria:

• Prior surgery or radiation to the head, neck, or upper chest (except surgeries such as tonsillectomy/adenoidectomy/tympanostomy that would not be expected, in the judgement of the investigator, to have disrupted the adipose tissue in the neck or the upper chest)
• Active addiction or illicit drug abuse
• BMI greater than 25
• Employment in the night shift/3rd shift
• Unable to remain in the Clinical and Translational Research Center (CTRC) for entire 24 hour period.
• Unable or unwilling to maintain peripheral intravenous access for up to 24 hours
• Abnormal liver or kidney function (serum creatinine or transaminase levels greater than 1.5 ULN)
• Subject has any other condition or personal circumstance that, in the judgement of the investigator, might interfere with the collection of complete, high quality data

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Diagnostic
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm

Intervention / Treatment

Other: Single group assignment; Diagnostic test/procedure - FDG PET/CT

Device: FDG PET/CT; PET/CT is a hybrid imaging modality that allows imaging positron emitting isotopes such as F-18 along with anatomic imaging using x-rays. The physiologic information from the PET component is co-registered with the anatomic information from the CT component, permitting accurate localization and quantification of physiologic processes. The most common clinically used positron emitting radiopharmaceutical is F-18 fluorodeoxyglucose (FDG). It is a glucose analog which is taken up by glucose transporters and phosphorylated to FDG-6P by hexokinase. FDG PET/CT gives a map of relative amount of glucose uptake and phosphorylation over the interval from injection to scan.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Time Frame
Change in Maximum Standardized Update Value (SUVmax) in Brown Adipose Tissue FDG Uptake in the Neck or Upper Chest on Evening and Imaging Compared to Morning Imaging	~12-hours

Secondary Outcome Measures

Outcome Measure	Time Frame
Correlation Between Cortisol Level and Brown Adipose Tissue FDG Uptake	~12-hours
Change in Total Brown Adipose Tissue FDG Uptake as Measured by Total Volume of Segmented Fat Times the Mean Standardized Uptake Value (SUVmean)	~12-hours

Collaborators and Investigators

• Sponsor: University of Pennsylvania

Publications and helpful links

Helpful Links

• The nuclear receptor Rev-erbα controls circadian thermogenic plasticity.

Study record dates

Study Major Dates

• Study Start: March 1, 2014
• Primary Completion (Actual): April 1, 2015
• Study Completion (Actual): April 1, 2015

Study Registration Dates

• First Submitted: November 4, 2014
• First Submitted That Met QC Criteria: November 5, 2014
• First Posted (Estimate): November 6, 2014

Study Record Updates

• Last Update Posted (Estimate): December 7, 2016
• Last Update Submitted That Met QC Criteria: October 25, 2016
• Last Verified: October 1, 2016

More Information

Terms related to this study

• Keywords: Circadian rhythm; Metabolism; Adipose tissue, brown
• Other Study ID Numbers: 819607