Triglyceride oxidation in cystic fibrosis: a comparison between different 13C-labeled tracer substances.

Background: For indirect evaluation of pancreatic lipase activity in cystic fibrosis, different 13 C-labeled triglycerides may be used. Methods: Triglyceride oxidation in patients with cystic fibrosis was investigated after administration of different 13 C-labeled triglycerides by comparing 13 CO 2 breath exhalation. In the comparative study, five patients with cystic fibrosis (age, 8-15 years; body weight, 22.5-39.8 kg) were treated with Pangrol (individual dosages: 1-3 capsules per morning meal; Berlin-Chemie, Berlin, Germany). [1,1,1- 13 C 3 ]Glyceryl tripalmitate and [1,1,1- 13 C 3 ]glyceryl trioleate were administered as a single oral pulse at 8:00 A.M. (dosage, 4 mg/kg each) with the standard diet Fresubin (dosage, 10 ml/kg; Fresenius, Bad Homburg, Germany). Alternately, the same subjects were given the synthetic mixed triglyceride 1,3-distearyl, 2[ 13 C]octanoyl glycerol (dosage, 12.5 mg/kg) contained in the standard diet Nutri-Mix (dosage, 10 ml/kg; Nutricia, Zoetemeer, The Netherlands). Breath samples were taken in 15- and 30-minute intervals over 8 hours. The 13 CO 2 enrichment was measured by continuous-flow isotope ratio mass spectrometry. Results: After administration of the 13 C-labeled tripalmitin-triolein mixture and the mixed triglyceride, mean maximum 13 CO 2 enrichments were 4.70 and 7.37 δ over baseline, occurring at 7.0 and 3.5 hours, respectively. The corresponding percentage cumulative 13 CO 2 exhalations were 12.25% and 29.19%, respectively, and differed significantly in the five paired subjects (p = 0.003). Conclusions: After using different 13 C-labeled triglycerides the resultant 13 CO 2 exhalation reflected the triglyceride hydrolysis and subsequent oxidation. It is concluded that the different cumulative 13 CO 2 exhalations were mainly caused by the rate-limiting step of triglyceride hydrolysis to free fatty acids and 2-monoglycerides and by fat deposition. Noninvasive 13 C breath tests using different 13 C-labeled triglycerides can be used for evaluation of pancreatic lipase activity before and during enzyme supplementation.