Metabolic handling of 13C labelled tripalmitin in healthy controls and patients with cystic fibrosis

Aim-To examine the gastrointestinal handling and metabolic disposal of emulsified [1-C-13]palmitic acid esterified into a triglyceride in nine healthy children and seven patients with cystic fibrosis on enzyme replacement treatment. Methods-After an overnight fast, each child was given 10 mg/kg body weight [1,1,1-C-13]tripalmitin with a standardised test meal of low natural C-13 abundance. The total enrichment of C- 13 was measured using isotope ratio mass spectrometry in stool collected for a period of up to five days and in breath samples collected over a 24 hour period. Results-The mean proportion of administered( 13)C label excreted in stool was 6% (range, 1-12.7%) in healthy children and 24.6% (range, 0-64%) in patients with cystic fibrosis. Healthy children excreted 31.3% of the administered label on their breath (range, 14.2-42.9%). Correcting the excretion of administered C-13 label on the breath for differences in digestion and absorption in patients with cystic fibrosis increased the difference between individuals from 0-31.3% of administered dose (mean, 17.9%) to 0-49.1% of absorbed dose (mean, 23.2%) and was poorly related to the amount of C-13 label in stool. Conclusion-Measurements of breath (CO2)-C-13 do not consistently reflect the gastrointestinal handling of emulsified C-13 labelled tripalmitin because of differences in digestion and absorption in cystic fibrosis. Further studies need to examine whether "breath tests" alone can predict with confidence the gastrointestinal handling of other C-13 labelled triglycerides and fatty acids.