A New Approach to Measuring Energy Expenditure in Humans
| Status: | Recruiting |
|---|---|
| Healthy: | No |
| Age Range: | 18 - 99 |
| Updated: | 4/21/2016 |
| Start Date: | September 2013 |
| End Date: | August 2016 |
Improvements to the Doubly Labeled Water Technique to Measure Total Daily Energy Expenditure
Accurately measuring how many calories a person burns each day is difficult to do.
Researchers can do this with a technique called doubly labeled water (DLW). This involves
drinking water that is "labeled" with a non-radioactive tracer. After a few hours, the
labeled water can be detected in the urine. To measure how many calories are burned (Total
daily energy expenditure, TDEE), urine samples are collected several days apart. Although
this technique is accurate, it is also challenging for two reasons. First, the labeled water
is expensive. Second, the urine samples are analyzed using equipment (Isotope Ratio Mass
Spectrometer, or IRMS) that is expensive and difficult to operate. The goal of this project
is to develop a new instrument to perform DLW measurements of TDEE. This instrument, called
a triple isotope water analyzer (TIWA) is less expensive and easier to operate than IRMS.
Additionally, since the TIWA is more accurate than IRMS, it may potentially reduce the
amount of labeled water required to measure TDEE, and thus reduce costs. The purpose of this
study is to compare the accuracy of measuring TDEE from labeled water using the new
instrument (TIWA) and from the traditional approach (IRMS). We will also compare the
accuracy to the measurement of TDEE from whole-room indirect calorimetry (metabolic room),
which is considered the most accurate way to measure TDEE.
Researchers can do this with a technique called doubly labeled water (DLW). This involves
drinking water that is "labeled" with a non-radioactive tracer. After a few hours, the
labeled water can be detected in the urine. To measure how many calories are burned (Total
daily energy expenditure, TDEE), urine samples are collected several days apart. Although
this technique is accurate, it is also challenging for two reasons. First, the labeled water
is expensive. Second, the urine samples are analyzed using equipment (Isotope Ratio Mass
Spectrometer, or IRMS) that is expensive and difficult to operate. The goal of this project
is to develop a new instrument to perform DLW measurements of TDEE. This instrument, called
a triple isotope water analyzer (TIWA) is less expensive and easier to operate than IRMS.
Additionally, since the TIWA is more accurate than IRMS, it may potentially reduce the
amount of labeled water required to measure TDEE, and thus reduce costs. The purpose of this
study is to compare the accuracy of measuring TDEE from labeled water using the new
instrument (TIWA) and from the traditional approach (IRMS). We will also compare the
accuracy to the measurement of TDEE from whole-room indirect calorimetry (metabolic room),
which is considered the most accurate way to measure TDEE.
The high prevalence of obesity in the US (17) is a major public health concern, as
overweight and obese individuals are at increased risk for many chronic diseases (5, 7, 15,
18). Obesity stems from an imbalance between total caloric consumption and total energy
expenditure (TEE), although the causes of this imbalance remain debated (29). Accurate and
precise measurements of TEE therefore play a pivotal role in understanding and ultimately
reversing this epidemic. TEE can be measured using direct (measurement of heat production)
or indirect (measurement of respiratory gas exchange) calorimetry (4), but neither of these
approaches are practical for measuring TEE in free living subjects. The gold standard for
measuring TEE in free-living individuals is the doubly labeled water (DLW) method, which is
based on the principle that the oxygen in body water is in complete isotopic equilibrium
with the oxygen in dissolved respiratory carbon dioxide due to the action of carbonic
anhydrase. The consequence of this exchange is that an isotopic label of oxygen introduced
into body water is eliminated by the combined flux of body water and the exhaled carbon
dioxide. Lifson and colleagues reasoned that, since hydrogen is found only in water and not
in carbon dioxide, the elimination of a hydrogen isotope would be affected solely by the
flux of body water (11). Thus the difference in the rates of isotope elimination of
simultaneously administered oxygen and hydrogen labels is a measure of CO2 production.
However, despite its widespread use (6, 9, 10, 20, 25, 29), the DLW method has some major
limitations. Individual measurements are only precise to ± 7 % at best (23), so the method
is currently most suitable for studies of groups rather than individual variation. A second
problem is that the test is expensive to perform due to the need for relatively large sample
sizes to achieve sufficient statistical power, the large quantities of H218O needed for
dosing (23), and IRMS analysis. High levels of 18O are required to distinguish the dose from
background isotope levels after 10 - 21 days of elimination. It currently costs $500 - $750
for the 18O required to perform a DLW measurement on an adult subject (50 - 75 kg fat free
mass) and the cost is unpredictable due to fluctuations in demand from the medical
diagnostic PET scan. The need for high 18O enrichments is caused by fluctuations in the
background isotope levels over time (8). This uncertainty in the background levels increases
the isotope dose that must be administered and contributes to the uncertainty in the DLW
measurements as compared to the reference calorimetry measurements of TEE in validation
studies. Finally, IRMS analysis presents its own set of challenges, including the need for
sophisticated, expensive instrumentation with dedicated, highly trained operators, and, in
general, measurement of only one isotope ratio at a time, reducing analytical throughput.
Because of these challenges, most researchers conducting DLW tests do not maintain in-house
IRMS facilities, relying instead on expensive and slow analyses by outside measurement
laboratories. The proposed work will address these problems by developing a new
triple-isotope method for DLW analysis, significantly improving the individual accuracy of
the measurements and reducing the cost of the DLW method, leading to more widespread use of
the DLW method in both clinical and research applications.
The overall goal of this Small Business Innovation Research (SBIR) Phase II grant is to
develop and validate a new instrument to measure and correct for the background isotope
levels of 18O and 2H during DLW analysis by measuring the 17O stable isotope of oxygen in
body water. This approach will address the two major limitations addressed above. First, by
using 17O measurements to correct for background fluctuations in 18O and 2H, this approach
will reduce the amount of 18O, and thus cost, of performing DLW studies. Results from our
Phase I studies (see Preliminary Data below) show that background fluctuations in 18O and
17O in body water are correlated with an R2 of 0.96, background fluctuations in 2H and 17O
are correlated with an R2 of 0.89, and background fluctuations in 2H and 18O are correlated
with an R2 of 0.92. Based on these correlations, using 17O measurements to estimate the
background fluctuations of the 2H and 18O will provide an estimated forty percent decrease
in the uncertainty of the DLW method due to background fluctuation. Second, The proposed
instrument will be utilized in the new, triple-isotope method for DLW which will reduce
existing barriers to widespread use of the DLW method by improving precision, reducing
costs, reducing the technical expertise required to perform the analysis, and increasing
throughput. Development of the new instrument will be performed by our business partners,
Los Gatos Research, and validation studies will be performed at the University of Colorado
Anschutz Medical campus.
In this work, we will apply Los Gatos Research's ultrasensitive absorption spectroscopy
technology, Off-Axis Integrated Cavity Output Spectroscopy (Off-Axis ICOS), to
simultaneously and inexpensively (< $50 per sample) measure 2H, 18O, and 17O in liquid water
samples. Briefly, in Off-Axis ICOS, laser light is coupled to an optical cavity in an
off-axis fashion and is continuously measured similar to a standard absorption experiment
(Figure 1) (1). The cavity provides an extraordinarily long effective optical pathlength
(e.g. typically 5 - 10 km) allowing for the accurate quantification of weakly absorbing
molecules. Moreover, since the off-axis beam path is not unique, the system is extremely
insensitive to changes in alignment, making it robust. This robustness combined with the
long effective optical pathlength makes it possible to measure water isotopomers with very
high precision. Since its development, Los Gatos Research (LGR) and its commercial customers
have performed many experiments to validate the sensitivity and robustness of Off-Axis ICOS
to measure a variety of trace gases including water isotopomers H2O, 1H2HO, and H218O (2,
12, 14, 19, 26, 27) and most recently water isotopomers in undistilled human urine (3).
overweight and obese individuals are at increased risk for many chronic diseases (5, 7, 15,
18). Obesity stems from an imbalance between total caloric consumption and total energy
expenditure (TEE), although the causes of this imbalance remain debated (29). Accurate and
precise measurements of TEE therefore play a pivotal role in understanding and ultimately
reversing this epidemic. TEE can be measured using direct (measurement of heat production)
or indirect (measurement of respiratory gas exchange) calorimetry (4), but neither of these
approaches are practical for measuring TEE in free living subjects. The gold standard for
measuring TEE in free-living individuals is the doubly labeled water (DLW) method, which is
based on the principle that the oxygen in body water is in complete isotopic equilibrium
with the oxygen in dissolved respiratory carbon dioxide due to the action of carbonic
anhydrase. The consequence of this exchange is that an isotopic label of oxygen introduced
into body water is eliminated by the combined flux of body water and the exhaled carbon
dioxide. Lifson and colleagues reasoned that, since hydrogen is found only in water and not
in carbon dioxide, the elimination of a hydrogen isotope would be affected solely by the
flux of body water (11). Thus the difference in the rates of isotope elimination of
simultaneously administered oxygen and hydrogen labels is a measure of CO2 production.
However, despite its widespread use (6, 9, 10, 20, 25, 29), the DLW method has some major
limitations. Individual measurements are only precise to ± 7 % at best (23), so the method
is currently most suitable for studies of groups rather than individual variation. A second
problem is that the test is expensive to perform due to the need for relatively large sample
sizes to achieve sufficient statistical power, the large quantities of H218O needed for
dosing (23), and IRMS analysis. High levels of 18O are required to distinguish the dose from
background isotope levels after 10 - 21 days of elimination. It currently costs $500 - $750
for the 18O required to perform a DLW measurement on an adult subject (50 - 75 kg fat free
mass) and the cost is unpredictable due to fluctuations in demand from the medical
diagnostic PET scan. The need for high 18O enrichments is caused by fluctuations in the
background isotope levels over time (8). This uncertainty in the background levels increases
the isotope dose that must be administered and contributes to the uncertainty in the DLW
measurements as compared to the reference calorimetry measurements of TEE in validation
studies. Finally, IRMS analysis presents its own set of challenges, including the need for
sophisticated, expensive instrumentation with dedicated, highly trained operators, and, in
general, measurement of only one isotope ratio at a time, reducing analytical throughput.
Because of these challenges, most researchers conducting DLW tests do not maintain in-house
IRMS facilities, relying instead on expensive and slow analyses by outside measurement
laboratories. The proposed work will address these problems by developing a new
triple-isotope method for DLW analysis, significantly improving the individual accuracy of
the measurements and reducing the cost of the DLW method, leading to more widespread use of
the DLW method in both clinical and research applications.
The overall goal of this Small Business Innovation Research (SBIR) Phase II grant is to
develop and validate a new instrument to measure and correct for the background isotope
levels of 18O and 2H during DLW analysis by measuring the 17O stable isotope of oxygen in
body water. This approach will address the two major limitations addressed above. First, by
using 17O measurements to correct for background fluctuations in 18O and 2H, this approach
will reduce the amount of 18O, and thus cost, of performing DLW studies. Results from our
Phase I studies (see Preliminary Data below) show that background fluctuations in 18O and
17O in body water are correlated with an R2 of 0.96, background fluctuations in 2H and 17O
are correlated with an R2 of 0.89, and background fluctuations in 2H and 18O are correlated
with an R2 of 0.92. Based on these correlations, using 17O measurements to estimate the
background fluctuations of the 2H and 18O will provide an estimated forty percent decrease
in the uncertainty of the DLW method due to background fluctuation. Second, The proposed
instrument will be utilized in the new, triple-isotope method for DLW which will reduce
existing barriers to widespread use of the DLW method by improving precision, reducing
costs, reducing the technical expertise required to perform the analysis, and increasing
throughput. Development of the new instrument will be performed by our business partners,
Los Gatos Research, and validation studies will be performed at the University of Colorado
Anschutz Medical campus.
In this work, we will apply Los Gatos Research's ultrasensitive absorption spectroscopy
technology, Off-Axis Integrated Cavity Output Spectroscopy (Off-Axis ICOS), to
simultaneously and inexpensively (< $50 per sample) measure 2H, 18O, and 17O in liquid water
samples. Briefly, in Off-Axis ICOS, laser light is coupled to an optical cavity in an
off-axis fashion and is continuously measured similar to a standard absorption experiment
(Figure 1) (1). The cavity provides an extraordinarily long effective optical pathlength
(e.g. typically 5 - 10 km) allowing for the accurate quantification of weakly absorbing
molecules. Moreover, since the off-axis beam path is not unique, the system is extremely
insensitive to changes in alignment, making it robust. This robustness combined with the
long effective optical pathlength makes it possible to measure water isotopomers with very
high precision. Since its development, Los Gatos Research (LGR) and its commercial customers
have performed many experiments to validate the sensitivity and robustness of Off-Axis ICOS
to measure a variety of trace gases including water isotopomers H2O, 1H2HO, and H218O (2,
12, 14, 19, 26, 27) and most recently water isotopomers in undistilled human urine (3).
Inclusion Criteria:
- Age > 18yrs
Exclusion Criteria:
- Smokers
- weight > 300 lbs
- chronic disease (e.g. diabetes, heart disease, thyroid disease)
We found this trial at
1
site
13001 E 17th Pl
Aurora, Colorado 80045
Aurora, Colorado 80045
(303) 724-5000
Principal Investigator: Edward L Melanson, Ph.D.
Phone: 303-724-0935
University of Colorado Anschutz Medical Campus Located in the Denver metro area near the Rocky...
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