OR22-6 Estimation of total body muscle mass from a urine sample using deuterated creatine (methyl-d3)

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: OR22-Male Reproductive Hormones: Effects on Fertility and Beyond
Sunday, June 16, 2013: 11:15 AM-12:45 PM
Presentation Start Time: 12:30 PM
Room 104 (Moscone Center)
Richard V Clark*1, Ann C Walker2, Robin L O'Connor-Semmes3, Michael S Leonard4, Ronald l Sanders5, Peixin Sun2, Ram R Miller1, Stephen A Stimpson1, Scott M Turner6, Marc K Hellerstein7, Eric Ravussin8, William T Cefalu9 and William J Evans1
1Muscle Metabolism DPU, GlaxoSmithKline R&D, Research Triangle Park, NC, 2Quant Science, GlaxoSmithKline R&D, Research Triangle Park, NC, 3Clin Pharmacol, GlaxoSmithKline R&D, 4Quant PK, GlaxoSmithKline R&D, Research Triangle Park, NC, 5Clin Ops, GlaxoSmithKline R&D, Research Triangle Park, NC, 6KineMed, Emeryville, CA, 7Dept Nutrional Sci, Univ of California-Berkeley, Berkeley, CA, 8Health Perf Enhancement, Pennington Biomed Res Ctr, Baton Rouge, LA, 9Diabetes Metab, Pennington Biomed Rsrch Ctr, Baton Rouge, LA
Background:  Current methods to clinically assess total body skeletal muscle mass have significant limitations in availability, precision, accuracy and cost.  Previously, in pre-clinical studies, we validated a method to estimate muscle mass using creatine (methyl-d3) dilution (D3-creatine) to determine total body creatine pool size (1). Objective:  We attempted to validate this model in humans, and to determine the appropriate dose of D3-creatine, the time to reach isotopic steady state of urinary creatinine enrichment, and if there is any loss of the orally administered D3-creatine in urine.

Design:  Thirty three healthy subjects were studied with a range of muscle mass:  13 men (18-45yr), 9 post-menopausal women (50-60yr), 11 elderly men and women (70-85yr).  Subjects were housed in an inpatient unit for a 5 day study.  After overnight fast, subjects received an oral dose of 30, 60, or 100mg of D3-creatine at 8AM on day 1.  Serial plasma samples were collected for measurement of D3-creatine for first 12 hr after dose, and for 72 hr in the older subjects.  Urine was collected continuously, beginning at baseline, day -1, and through day 5 of the study.  Measurement of plasma and urine creatine and creatinine, deuterated and unlabeled, was done by liquid chromatography/mass spectrometry (LC/MS/MS).  Total body creatine pool size and muscle mass were calculated from D3-creatinine enrichment in urine.  Total body muscle mass was also measured by MRI (serial cross sections) and lean body mass (LBM) by DEXA.

Results:   The D3-creatine was rapidly absorbed and removed from plasma (95%) within 12 hr of the oral tracer dose.  The % of D3-creatine dose excreted in urine varied by age and gender group, lowest in young men (median <1%) and highest in women (medians 16-25%).  The majority of D3-creatine excretion occurred in first 24hrs post-dose.  Isotopic steady state of excreted D3-creatinine was achieved by 30.7 ± 11.3 hr, and remained at steady-state through 120 hr post-dose.  D3-enrichment from urine samples on Day 4 provided estimates of muscle mass that correlated well with the muscle mass estimate by MRI for all subjects (r = 0.87, P < 0.0001 after adjusting for gender), and provided an estimate of muscle mass with less bias compared to LBM assessment by DEXA, which also has strong correlation with MRI but overestimates muscle mass.

Conclusions:  Determination of dilution of an oral D3-creatine dose through a urine sample provides an estimate of total body muscle mass based on creatine pool size that is strongly correlated to estimates from serial MRI with less bias than lean mass assessment by DEXA.  Further studies to determine reproducibility and prediction of D3-creatine excretion in urine are planned. This method has potential for a more facile measurement of skeletal muscle mass in patients experiencing muscle wasting in a variety of conditions, for diagnosis and for following response to therapy.

Stimpson SA et al, J Appl Physiol 2012; 112:1940

Disclosure: RVC: Employee, GlaxoSmithKline, Employee, GlaxoSmithKline. ACW: Employee, GlaxoSmithKline, Employee, GlaxoSmithKline. RLO: Employee, GlaxoSmithKline, Employee, GlaxoSmithKline. MSL: Employee, GlaxoSmithKline, Employee, GlaxoSmithKline. RLS: Employee, GlaxoSmithKline, Employee, GlaxoSmithKline. PS: Employee, GlaxoSmithKline, Employee, GlaxoSmithKline. RRM: Employee, GlaxoSmithKline, Employee, GlaxoSmithKline. SAS: Employee, GlaxoSmithKline, Employee, GlaxoSmithKline. SMT: Employee, KineMed, Employee, KineMed. MKH: Scientific Board Member, KineMed, Scientific Board Member, KineMed. WJE: Employee, GlaxoSmithKline, Employee, GlaxoSmithKline. Nothing to Disclose: ER, WTC

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: GlaxoSmithKline Research and Development
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