Longitudinal determination of total body creatine pool size and skeletal muscle mass in rats by D 3 ‐creatine dilution

• Published in: The FASEB journal Vol. 27; no. S1
• Main Authors: Stimpson, Stephen A., Leonard, Michael S., Clifton, Lisa G., Poole, James C., Turner, Scott M., Shearer, Todd W., Remlinger, Katja S., Clark, Richard V., Hellerstein, Marc K., Evans, William J.
• Format: Journal Article
• Language: English
• Published: 01-04-2013
• ISSN: 0892-6638; 1530-6860
• DOI: 10.1096/fasebj.27.1_supplement.lb410

Abstract only
We recently described a new method to determine total body creatine pool size and skeletal muscle mass based on dilution of an oral dose of D
3
‐creatine in urinary creatinine. Enrichment of D
3
‐ creatinine was measured by isotope ratio mass spectrometry. Here we adapt the method to LC‐MS/MS, and investigate the potential for repeated application over time. Rats were given an oral tracer dose of D
3
‐creatine (1.0 mg/kg body weight) at 10 weeks of age. Urine D
3
‐creatinine enrichment was determined 72 hr after tracer administration and creatine pool size was calculated. Lean body mass (LBM) measured by quantitative magnetic resonance correlated with creatine pool size (
r
= 0.92,
P
= 0.0002). The rate constant for decline in urinary D
3
‐creatinine enrichment was slow and linear (2.73 ± 0.06 %/day). Subtracting background urinary D
3
‐creatinine enrichment from the enrichment following a second dose of D
3
‐creatine at 17 weeks permitted repeat calculations of creatine pool size. As at 10 weeks, 17 week LBM correlated with creatine pool size (
r
= 0.98,
P
< 0.0001). In addition, the change in creatine pool size was correlated with the change in LBM during the 7 weeks of somatic growth between measurements (
r
= 0.96,
P
< 0.0001). Thus, the LC‐MS/MS‐based D
3
‐creatine dilution method can be applied repeatedly to measure skeletal muscle mass change in longitudinal studies. These studies were funded by GlaxoSmithKline.