Session: SUN 176-202-Male Reproductive Endocrinology and Male Reproductive Tract (posters)
Bench to Bedside
Poster Board SUN 182
Design: Fourteen healthy older men (10) and women (4) aged 65-85yr; and 4 male patients with CHF (2) or COPD (2) aged 50-85yr, were evaluated at baseline. Repeat assessment was done at 3-4 months after baseline in 13 of the older participants and 1 patient with CHF. For each determination, subjects were housed in an inpatient unit for 5 days. After an overnight fast, subjects received an oral dose of 30mg of D3-creatine at 8AM on day 1 and continued to fast for 4 hrs while urine was collected (0-4hr). Urine was then continuously collected at consecutive intervals of 4-8hr through day 5 of the study. Measurement of urine creatine and creatinine, deuterated and unlabeled, was performed 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 whole-body MRI (serial cross sections) and lean body mass (LBM) by DXA.
Results: The percent of D3-creatine dose excreted in urine was lower in men (median 3.5%) than in women (median 25.6%). The majority of D3-creatine excretion occurred in first 24hrs post-dose. Median time to isotopic steady state of excreted D3-creatinine was achieved by 26 hrs in men and 52 hrs in women. D3-enrichment from fasted, morning urine samples on Day 5 (96-100hr), when corrected for measured D3-creatine excretion, provided estimates of muscle mass that correlated well with MRI for all subjects (r = 0.91, P < 0.0001), and with less bias (mean ± SD difference from MRI: -2.91kg ± 2.63kg) compared to total LBM assessment by DXA, which overestimated muscle mass vs MRI (+22.49 ± 3.71kg). However, intra-individual variability was high with the D3-creatine method, with intra-subject SD for estimate of muscle mass of 2.1kg vs MRI (0.5kg) and DXA (0.8kg).
Conclusions: This study gives further confirmation that the D3 creatine dilution method provides an estimate of total body muscle mass based on creatine pool size that is strongly correlated to estimates from MRI with less bias than by DXA which markedly overestimates lean mass. However, the variability of this method may limit its application to broad categorization of muscle mass in population subgroups rather than assessment of individual change in muscle mass related to disease states or in response to therapeutic interventions.
Disclosure: RVC: Clinical Researcher, GlaxoSmithKline. ACW: Clinical Researcher, GlaxoSmithKline. RRM: Clinical Researcher, GlaxoSmithKline, Clinical Researcher, Novartis Pharmaceuticals, Clinical Researcher, GlaxoSmithKline. RLO: Employee, Parexel International. WTC: Principal Investigator, Astra Zeneca, Principal Investigator, Eli Lilly & Company, Principal Investigator, Lexicon Pharmaceuticals, Inc., Principal Investigator, Sanofi, Consultant, Sanofi, Principal Investigator, GlaxoSmithKline, Principal Investigator, Johnson &Johnson, Consultant, Intarcia. Nothing to Disclose: ER
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