title: Serum glycine is associated with regional body fat and insulin resistance in functionally-limited older adults.
abstract: BACKGROUND
  Metabolic profiling may provide insight into biologic mechanisms related to age-related increases in regional adiposity and insulin resistance.
  
  
  OBJECTIVE
  The objectives of the current study were to characterize the association between mid-thigh intermuscular and subcutaneous adipose tissue (IMAT, SCAT, respectively) and, abdominal adiposity with the serum metabolite profile, to identify significant metabolites as further associated with the homeostasis model assessment of insulin resistance (HOMA-IR), and, to develop a HOMA-IR associated metabolite predictor set representative of regional adiposity, in 73 functionally-limited (short physical performance battery ≤10; SPPB) older adults (age range, 70-85 y).
  
  
  METHODS
  Fasting levels of 181 total metabolites, including amino acids, fatty acids and acylcarnitines were measured with use of an untargeted mass spectrometry-based metabolomic approach. Multivariable-adjusted linear regression was used in all analyses.
  
  
  RESULTS
  Thirty-two, seven and one metabolite(s) were found to be associated with IMAT, abdominal adiposity and, SCAT, respectively, including the amino acid glycine, which was positively associated with SCAT and, negatively associated with both IMAT and abdominal adiposity. Glycine and four metabolites found to be significantly associated with regional adiposity were additionally associated with HOMA-IR. Separate stepwise regression models identified glycine as a HOMA-IR associated marker of both IMAT (model R(2) = 0.51, p<0.0001) and abdominal adiposity (model R(2) = 0.41, p<0.0001).
  
  
  CONCLUSIONS
  Our findings for a positive association between glycine with SCAT but, a negative association between glycine with IMAT and abdominal adiposity supports the hypothesis that SCAT metabolic processes are different from that found in other fat depots. In addition, because of the significant associations found between glycine with HOMA-IR, IMAT, SCAT and abdominal adiposity, our results suggest glycine as a serum biomarker of both insulin sensitivity and regional fat mass in functionally-limited older adults.
authors.affiliation: Nutrition, Exercise Physiology, and Sarcopenia Laboratory, Jean Mayer USDA Human Nutrition Research Center, Tufts University, Boston, Massachusetts, United States of America.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Lustgarten
authors.affiliation: The Institute for Clinical Research and Health Policy Studies, Tufts Medical Center, and Tufts Clinical and Translational Science Institute, Tufts University, Boston, Massachusetts, United States of America.
authors.forename: Lori Lyn
authors.initials: LL
authors.lastname: Price
authors.affiliation: Nutrition, Exercise Physiology, and Sarcopenia Laboratory, Jean Mayer USDA Human Nutrition Research Center, Tufts University, Boston, Massachusetts, United States of America.
authors.forename: Edward M
authors.initials: EM
authors.lastname: Phillips
authors.affiliation: Nutrition, Exercise Physiology, and Sarcopenia Laboratory, Jean Mayer USDA Human Nutrition Research Center, Tufts University, Boston, Massachusetts, United States of America.
authors.forename: Roger A
authors.initials: RA
authors.lastname: Fielding
mesh_terms: D000273:Adipose Tissue / Q000502:physiology*; D050154:Adiposity / Q000502:physiology*; D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood*; D002853:Chromatography, Liquid; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D005998:Glycine / Q000097:blood*; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D007333:Insulin Resistance / Q000502:physiology*; D008297:Male; D055432:Metabolomics; D011379:Prognosis; D053719:Tandem Mass Spectrometry
chemical_list: D015415:Biomarkers; D005998:Glycine