phosphorus-31-magnetic-resonance-spectroscopy-tool-for-measuring-vivo

Phosphorus-31 Magnetic Resonance Spectroscopy: A Tool for Measuring <em>In Vivo</em> Mitochondrial Oxidative Phosphorylation Capacity in Human Skeletal Muscle

Skeletal muscle mitochondrial oxidative phosphorylation (OXPHOS) capacity, which is critically important in health and disease, can be measured in vivo ...

The Ohio State University

Glucagon-like peptide-1 (GLP-1) is a gastrointestinal hormone mainly released from the distal ileum, jejunum, and colon in response to food ingestion. It is categorized as an incretin due to its activation of GLP-1 receptors in pancreatic beta-cells leading to insulin exocytosis in a glucose-dependent manner. Exenatide (synthetic exendin-4) is a subcutaneously injected GLP-1 receptor agonist that shares 50% homology with GLP-1. It is derived from lizard venom and stimulates the GLP-1 receptor for prolonged periods. The present review aims to enumerate exenatide-instigated weight loss, summarize the known mechanisms of exenatide-induced weight loss, and elaborate on its possible application in the pharmacotherapy of obesity.

Exenatide and weight loss.

Individuals who smoke generally have a lower body mass index (BMI) than nonsmokers. The relative roles of energy expenditure and energy intake in maintaining the lower BMI, however, remain controversial. We tested the hypothesis that current smokers have higher total energy expenditure than never smokers in 308 adults aged 40-69 years old of which 47 were current smokers. Energy expenditure was measured by doubly labeled water during a two week period in which the subjects lived at home and performed their normal activities. Smoking status was determined by questionnaire. There were no significant differences in mean BMI (mean ± SD) between smokers and never smokers for either males (27.8+5.1 kg/m2 vs. 27.5+4.0 kg/m2) or females (26.5+5.3 kg/m2 vs. 28.1+6.6 kg/m2), although the difference in females was of similar magnitude to previous reports. Similarly, total energy expenditure of male smokers (3069+764 kcal/d) was not significantly different from that of never smokers (2854+468 kcal/d), and that of female smokers (2266+387 kcal/d) was not different from that of never smokers (2330+415 kcal/d). These findings did not change after adjustment for age, fat-free mass and self-reported physical activity. Using doubly labeled water, we found no evidence of increased energy expenditure among smokers, however, it should be noted that BMI differences in this cohort also did not differ by smoking status.

Effect of smoking status on total energy expenditure.

Exenatide is a medication similar in structure and effect to native glucagon-like peptide-1, an incretin hormone with glucose-lowering properties. The aim of the study was to measure the change in total energy expenditure (TEE) and body composition during exenatide administration and by deduction the relative contributions of energy expenditure and energy intake to exenatide-induced weight loss. Forty-five obese (body mass index, 30-40 kg·m⁻²) subjects were identified. After exclusion criteria application, 28 subjects entered into the study and 18 subjects (12 female, 6 male) completed the study, which consisted of 6 visits over 14 weeks and injection of exenatide for an average of 84 ± 5 days. Respiratory gas analysis and doubly labeled water measurements were performed before initiation of exenatide and after approximately 3 months of exenatide administration. The average weight loss from the beginning of injection period to the end of the study in completed subjects was 2.0 ± 2.8 kg (p = 0.01). Fat mass declined by 1.3 ± 1.8 kg (p = 0.01) while the fat-free mass trended downward but was not significant (0.8 ± 2.2 kg, p = 0.14). There was no change in weight-adjusted TEE (p = 0.20), resting metabolic rate (p = 0.51), or physical activity energy expenditure (p = 0.38) and no change in the unadjusted thermic effect of a meal (p = 0.37). The significant weight loss because of exenatide administration was thus the result of decreasing energy intake. In obese nondiabetic subjects, exenatide administration did not increase TEE and by deduction the significant weight loss and loss of fat mass was due to decreased energy intake.

Article	Year
Exenatide and weight loss. Nutrition (Burbank, Los Angeles County, Calif.)\| PubMed ID: 20152707	2010
Effect of smoking status on total energy expenditure. Nutrition & metabolism\| PubMed ID: 21040542	2010
Alterations in energy balance following exenatide administration. Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme\| PubMed ID: 22735035	2012

David P. Bradley

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