Longitudinal changes in total body creatine pool size and skeletal muscle mass using the D₃-creatine dilution method

Area of Science:

• Biomedical science
• Physiology
• Analytical chemistry

Background:

• Cross-sectional studies validated a creatine dilution method for total body creatine pool size and skeletal muscle mass using D3-creatine and isotope ratio mass spectrometry (IRMS).
• Routine clinical application in aging and disease requires a more accessible technology than IRMS for longitudinal studies.
• Adapting the method to liquid chromatography-tandem mass spectrometry (LC-MS/MS) and assessing its longitudinal application is crucial.

Purpose of the Study:

• To adapt the D3-creatine dilution method to LC-MS/MS technology for longitudinal studies.
• To establish proof of concept for repeated application of the method in a longitudinal study.
• To determine the impact of background D3-creatine enrichment on subsequent measurements.

Main Methods:

• Rats received oral D3-creatine tracer doses at 10 and 17 weeks of age.
• LC-MS/MS was used to measure urinary D3-creatine and D3-creatinine enrichment.
• Total body creatine pool size was calculated from urinary D3-creatinine enrichment at isotopic steady state.

Main Results:

• Lean body mass (LBM) in rats correlated significantly with creatine pool size at both 10 and 17 weeks of age.
• The decline in urinary D3-creatinine enrichment was slow and linear, allowing for repeat measurements.
• Changes in creatine pool size strongly correlated with changes in LBM over the 7-week growth period.

Conclusions:

• The LC-MS/MS-based D3-creatine dilution method is suitable for repeated application in longitudinal studies.
• This method enables accurate measurement of total body creatine and skeletal muscle mass changes over time.
• The study provides a validated, accessible tool for longitudinal body composition analysis.