Identification of Muscle-specific Biomarkers of Fatty Acid Beta-oxidation
Condition: Obesity
Study type: Interventional

Summary: 
      Elevated fat levels within skeletal muscle cells (intramyocellular lipids) are highly
      correlated with muscle and whole-body insulin resistance, and more prevalent in obesity. The
      molecular links and metabolic shifts driving this association remain open to debate, but
      notably, reduced muscle mitochondrial fatty acid (FA) ß-oxidation is more prevalent among
      insulin-resistant/diabetic persons. Therefore, discovery of biomarkers reflective of the
      status of an individual's muscle FA ß-oxidation activity or capacity would have tremendous
      prognostic and diagnostic value in terms of diabetes. Furthermore, characterization of
      metabolites associated with muscle mitochondrial fat metabolism should uncover candidate
      signaling factors which tie FA ß-oxidation to insulin signaling. The investigators propose to
      identify, for the first time, specific biomarkers of muscle FA ß-oxidation using multiple
      metabolomic analytical platforms to compare metabolite profiles in samples derived from
      biological systems displaying disparate muscle fat combustion. The current experiment will
      test whether plasma metabolites and/or metabolite signatures that track efficient muscular FA
      ß-oxidation can be experimentally increased in obese, insulin-resistant subjects via a
      diet-exercise regimen designed to improve muscle fitness and FA combustion.
    

Detailed description: 
      The investigators will use several comprehensive state-of-the-art metabolite analysis
      platforms to test the hypothesis that specific systemic metabolites or metabolite signatures
      correlate with myocellular fatty acid combustion. The investigators will then determine
      whether said metabolites do in fact reflect metabolic health status as predicted, by
      determining whether profiles are altered in obese subjects whose insulin sensitivity and
      muscle FA ß-oxidation is improved through aerobic exercise and dietary intervention.
      Specifically, this study is investigating the usefulness of metabolomic profiles reflective
      of muscle fat combustion in predicting metabolic health changes following diet & exercise
      intervention in obese subjects. The investigators hypothesize that biomarkers reflective of
      normal, efficient muscle ß-oxidation will be increased, and markers indicative of poor muscle
      fat combustion reduced, in a cohort of sedentary obese subjects after undergoing a 4 month
      diet-exercise protocol that will increase muscle fitness and improve insulin action.

      In anticipation of 16 subjects completing the study, up to 20 obese female subjects will be
      recruited from the Davis and Sacramento areas and asked to participate in a weight loss
      regimen involving caloric restriction (reduction of ~25% of typical caloric intake, with
      rotating 7-day menus based on nutrient compositions reflective of the U.S. Dietary
      Guidelines) and regular aerobic exercise designed to target a 10% weight loss over 4 months
      (Goodpaster et al.,Diabetes 52: 2191-97, 2003). Volunteers to be included in this study will
      have the following characteristics: age 30-50, BMI between 30-34.9 with stable self-reported
      body weight over the last 6 mos., sedentary (not participating in a regular exercise program,
      typical planned exercise ≤30 min. per week assessed by pre-screening telephone
      questionnaire), non-smoker, no clinical signs of infection (i.e., no fever, CBC wnl), no
      personal history of cardiovascular disease, no clinically-significant elevations in blood
      pressure, or diabetes, no regular medications (except oral contraceptives, allergy meds) or
      drug abuse. These initial studies will involve women only in order to (a) reduce potential
      sex-related metabolite variability and (b) to better match subject characteristics in
      previous studies. Each subject will serve as her own control, with changes in metabolite
      profiles following intervention calculated for each individual. Post-absorptive insulin and
      glucose measurements will be made to estimate insulin sensitivity by HOMA, and patterns
      following an OGTT pre- and post-treatment used to assess the insulin sensitivity index using
      the method of Matsuda et al. (Matsuda & DeFronzo, Diabetes Care 22:1462-70, 1999). Individual
      changes in HOMA and insulin sensitivity values comparing pre- and post-intervention periods
      will be considered to be indicative of changes in insulin action. An acute exercise protocol
      to elicit muscle work will be carried out over 20 min. to increase metabolic flux of FA in
      muscle, a strategy designed to enrich the plasma with muscle metabolites. Differences in
      outcome variables will be tested by repeated-measures ANOVA to determine significance of
      fitness intervention exercise bout, and intervention exercise bout interactions.

      Screening: After signing the Consent Form, an initial fasting blood draw (up to 20 mL) and
      vital signs will be taken to ensure potential subjects meet the clinical criteria. Height and
      weight will be determined and interviews conducted to evaluate whether they meet the
      aforementioned criteria. Body weight will be measured to the nearest 0.1kg with subjects
      wearing light-weight surgical scrubs. Height will be measured to the nearest 0.1cm using a
      wall-mounted, Ayrton Stadiometer Model S100 (Ayrton Corporation, Prior Lake, MN). Body Mass
      Index (BMI) will be calculated as kg/m2. Waist circumference will be measured in the standing
      position, with measurements obtained midway between the lateral lower rib margin and the
      iliac crest. The measurement will be taken mid-exhalation, and the average of two readings
      will be recorded. Hip circumference will be measured at the maximum protuberance of the
      buttocks. An additional 5 mL of blood will be drawn 2 hours after subjects consume a drink
      containing a 75 g dose of sugar (an abbreviated oral glucose tolerance test) in order to
      evaluate insulin sensitivity. A Baecke questionnaire will be used to assess physical activity
      level to be used in DRI calculations of maintenance calories for the pre-intervention
      lead-in. To minimize variability in our outcome measures that may be introduced by menstrual
      cycle hormonal shifts, we will endeavor to maintain consistency by evaluating subjects during
      the follicular phase of the menstrual cycle (as estimated by cycle records for each woman),
      preferably beginning on day 4 of the menstrual cycle. Subjects on birth control medication
      will also preferably be evaluated on day 4 of their menstrual cycle. Subjects will be given a
      calendar and instructions to record their menstrual cycles throughout the study. Eligible
      subjects will be asked to visit the WHNRC several times, as follows:

      Test Week 1: On day 4 of their menstrual cycle, subjects will come to the clinic for the
      beginning of Test Week 1. Each day subjects will be given prepared meals to be eaten at the
      WHNRC, or packed to go along with final preparation instructions. During the test week
      subjects will receive meals and snacks for a 7 day menu prepared by the WHNRC Metabolic
      Kitchen and based on U.S. Dietary Guidelines and prescribed to maintain stable body weight.
      Volunteers will be provided with a daily multivitamin supplement study and will be required
      to refrain from taking personal dietary supplements or vitamins during the study. This is
      designed to ensure a similar nutritional profile across all subjects, prior to obtaining
      biofluids for metabolomic analysis to minimize physiological variability. Subjects will be
      weighed daily during Test weeks 1 and 2 to ensure body weight maintenance and diet
      prescriptions adjusted if necessary. During this test week each subject will participate in
      an instruction session regarding the diet and diet compliance provided under the guidance of
      a registered dietitian. This instruction may be done individually or in a group setting. Each
      individual's diet (based on the U.S. Dietary Guidelines) and exercise plan will be designed
      to elicit a target of 10% body weight loss and to improve fitness over the 16 week
      intervention period. Test Week 2: Test week 2 duplicates Test Week 1. Subjects will be
      scheduled based on predictions from their menstrual calendars. This might mean that subjects
      will continue exercising for additional days in order to coincide with menstrual day 4 when
      diet is provided and testing begins. The acute exercise will be a 40-50% of the Test week 1
      VO2max.
    

Intervention name(s): Diet and Exercise
Intervention type(s): Behavioral
Intervention description(s): Subjects underwent a diet regimen targeted to elicit a 10% weight loss. Diets were designed based on the US Dietary Guidelines with caloric deficits individualized for each subject. Aerobic exercise was monitored over approximately 14 weeks, several times per week, to elicit significantly increased VO2max.
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: Diabetes; Pre-diabetes; Obese