title: Isotopic decay of urinary or plasma 3-methylhistidine as a potential biomarker of pathologic skeletal muscle loss.
abstract: BACKGROUND
  Skeletal muscle loss accompanying aging or cancer is associated with reduced physical function and predicts morbidity and mortality. 3-Methylhistidine (3MH) has been proposed as a biomarker of myofibrillar proteolysis, which may contribute to skeletal muscle loss.
  
  
  METHODS
  We hypothesized that the terminal portion of the isotope decay curve following an oral dose of isotopically labeled 3MH can be measured non-invasively from timed spot urine samples. We investigated the feasibility of this approach by determining isotope enrichment in spot urine samples and corresponding plasma samples and whether meat intake up to the time of dosing influences the isotope decay.
  
  
  RESULTS
  Isotope decay constants (k) were similar in plasma and urine, regardless of diet. Post hoc comparison of hourly sampling over 10 h with three samples distributed over 10 or fewer hours suggests that three distributed samples over 5-6 h of plasma or urine sampling yield decay constants similar to those obtained over 10 h of hourly sampling.
  
  
  CONCLUSIONS
  The findings from this study suggest that an index of 3MH production can be obtained from an easily administered test involving oral administration of a stable isotope tracer of 3MH followed by three plasma or urine samples collected over 5-6 h the next day.
authors.affiliation: Departments of Internal Medicine, University of Texas Medical Branch, 301 University Blvd, Galveston, TX, 77555, USA.
authors.forename: M
authors.initials: M
authors.lastname: Sheffield-Moore
authors.forename: E L
authors.initials: EL
authors.lastname: Dillon
authors.forename: K M
authors.initials: KM
authors.lastname: Randolph
authors.forename: S L
authors.initials: SL
authors.lastname: Casperson
authors.forename: G R
authors.initials: GR
authors.lastname: White
authors.forename: K
authors.initials: K
authors.lastname: Jennings
authors.forename: J
authors.initials: J
authors.lastname: Rathmacher
authors.forename: S
authors.initials: S
authors.lastname: Schuette
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authors.lastname: Janghorbani
authors.forename: R J
authors.initials: RJ
authors.lastname: Urban
authors.forename: V
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authors.lastname: Hoang
authors.forename: M
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authors.lastname: Willis
authors.forename: W J
authors.initials: WJ
authors.lastname: Durham