1. Our ongoing clinical protocol titled Energy expenditure responses to a range of environmental temperatures around the thermal neutral zone (12-DK-0097, NCT01568671) was developed to improve our understanding of human dynamic regulation of energy expenditure in response to subtle changes in environmental temperature. In particular, we are interested in studying the capacity of facultative thermogenesis, defined as an increase in energy expenditure (EE or heat production) to a changed environmental temperature. Combined with the ongoing research on brown adipose tissue and its role in non-shivering thermogensis in our and other labs, such clinical research is generating substantial interests in the field of energy metabolism and obesity. We measured resting energy expenditure in a 5-hour period in the room calorimeter with randomized environmental temperature ranging between 16C and 31C, in 10-13 consecutive days (a 2-week inpatient protocol). We also carefully measured potential shivering by surface electromyography (EMG), acceleration, and heart rate, skin and core body temperatures, and stress responses by blood and urinary markers, while controlling for physical activity, clothing, posture, and dietary intake. The first (and the primary) hypothesis is that the lower critical temperature (that defines the beginning of cold-induced thermogenesis) will be reduced in obese as compared to non-obese subjects. To date, we have successfully studied fifteen (15) healthy lean male volunteers as our normative control group and six (6) healthy obese male volunteers matched for age and race/ethnicity. Preliminary data analyses showed that we could reproduce the resting EE in the thermal neutral zone (TNZ) within 2.5% coefficient of variation, detect shivering onset with EMG and heart rate, and the slope and the maximum capacity of non-shivering thermogenesis (in lean more so than in the obese), all of which are helping us to understand the parameters that define the dynamic human thermobiology to a range of environmental temperatures that have not been available. We are also observing a relatively blunted thermogenic response under the same level of cooling in obese subjects but in the same time, these subjects begin the shiver similar room temperature as the lean subjects;however, we need to accrual more obese subjects to confirm our preliminary observations. However, we have experienced increased difficulties successfully recruiting healthy obese young males due to multiple failed screenings and hesitations to commit to the 2-week inpatient stays without the benefits of losing weight. We are increasing our efforts to recruit in a broader area and hoping that will lead to the completion of 12 obese subjects in FY15. 2. At the end of FY13, we developed a new clinical protocol to use a pharmacologic approach to dissect the mechanism of NST (13-DK-0200, NCT01950520). Since the principal physiologic stimulus to BAT (and possibly muscle) NST is via sympathetic nervous system, we hypothesize that, by careful measurements of NST and using -adrenergic drugs that differ in receptor specificity and agonist/antagonist properties, we will gain better understanding of the regulation of human NST and resting EE. The second phase of the study focuses on measuring anti-obesity drugs potential effect on basal metabolic rate. The rationale is that previous studies of drug effect on EE in humans have not always rigorously enforced the use of thermoneutrality, thus may have increased variability and underestimated effects, contributing to inconclusive findings. We have studied six (6) healthy subjects to date for the first phase, and fully prepared to increase the recruitment in this phase and begin the second phase in FY15. 3. We followed up on the past studies (through collaborations with Dr. Francesco Celi) which we successfully linked measured BAT activation via 18F-fluro-deoxyglucose (FDG) positron emission tomography (PET) with individual acute (12-hr overnight) cold-induced thermogenesis in a group of non-obese men and women, we designed and conducted a clinical trial (13-DK-0013, ClinicalTrials.gov:NCT01730105 ) to investigate if BAT can be recruited by a lower ambient temperature at nighttime. This was a 4-month prospective crossover design with four consecutive blocks of 1-month overnight inpatient temperature acclimation (24C, 19C, 24C, and 27C). Five healthy young males completed the study, and demonstrated that BAT abundance and activity was boosted by cold exposure (19C), and reversely suppressed by warm (27C). We further demonstrated that the degree of BAT modulation after cold acclimation was associated to diet-induced thermogenesis and post-prandial insulin sensitivity. These results suggest regulatory links between BAT thermal plasticity and glucose metabolism in humans, opening avenues to harnessing BAT for potential metabolic benefits in the area of glucose utilization more so than just thermogenesis. 4. In 2012-13, Irisin and FGF21 became interesting targets of research as potential modulators for BAT and perhaps beige fat. Collaborating with Dr. Celi and his fellow Dr. Paul Lee, we conducted a series of studies under the protocols 07-DK-0202 and 13-DK-0013 (ClinicalTrials.gov:NCT 00521729 and 01730105, respectively). we explored whether cold exposure is an afferent signal for irisin secretion in humans and compared it with FGF21, a brown adipokine in rodents. Cold exposure increased circulating irisin and FGF21. In ten (10) subjects, we found an induction of irisin secretion proportional to shivering intensity, in magnitude similar to exercise-stimulated secretion. Irisin (FNDC5) and/or FGF21 treatment upregulated human adipocyte brown fat gene/protein expression and thermogenesis in a depot-specific manner. These results suggest exercise-induced irisin secretion could have evolved from shiveringrelated muscle contraction, serving to augment brown fat thermogenesis in concert with FGF21. Irisin-mediated muscle-adipose crosstalk may represent a thermogenic, cold-activated endocrine axis that is exploitable in obesity therapeutics development.
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