Advantages of deuterium-labelled mixed triacylglycerol in studies of intraluminal fat digestion.
The (13)C-mixed triacylglcerol (MTG, 1,3-distearyl, 2-[1-(13)C]octanoyl glycerol) breath test is a non-invasive measure of intraluminal fat digestion. Recovery of (13)C in breath CO(2) is incomplete (<50%) owing to sequestration of (13)C into organic molecules via the tricarboxylic acid (TCA) cycle. In addition lack of knowledge of CO(2) production rate (VCO(2)) during the test leads to errors in the calculated percentage dose recovered (PDR). (2)H sequestration into organic molecules is low ( approximately 4%) and is not influenced by factors that affect VCO(2) such as food intake or physical activity. After oxidation of (2)H-labelled macromolecules, the label appears in body water, which can be sampled non-invasively in urine or saliva. After an overnight fast, two healthy adults consumed [(2)H]MTG (1,3-distearyl, 2-[(2)H(15)]octanoyl glycerol) and [(13)C]MTG (1,3 distearyl, 2-[1-(13)C]octanoyl glycerol) simultaneously. Total body water (TBW) was measured by (18)O dilution and also estimated from height and weight. Urine and saliva were sampled at baseline and for 10 h after consumption of the test meal. The abundance of (2)HOH and H(2) (18)O in urine and saliva was measured by continuous-flow isotope-ratio mass spectrometry. Cumulative PDR of (2)H and (18)O was calculated from the plateau enrichment, which was reached by 6 h in both saliva and urine. Recovery of (2)H calculated using measured TBW was compared with that using an estimated value of TBW. Mean recovery of (2)H in saliva was 99.3% and in urine was 96.4%. Errors introduced by estimating TBW were <5%. [(2)H]MTG could provide a simpler, more robust, indirect test of intraluminal fat digestion compared with the (13)C-breath test. Further studies are required in pancreatic insufficient patients.
Slater
Christine
C
University of Glasgow, Division of Developmental Medicine, Royal Hospital for Sick Children, Yorkhill Hospitals, Glasgow G3 8SJ, UK. slater_christine@yahoo.co.uk
Preston
Tom
T
Weaver
Lawrence T
LT
D000284:Administration, Oral; D001944:Breath Tests / Q000379:methods; D002250:Carbon Radioisotopes / Q000008:administration & dosage / Q000032:analysis; D003903:Deuterium / Q000008:administration & dosage / Q000032:analysis; D004041:Dietary Fats / Q000378:metabolism*; D004063:Digestion / Q000502:physiology*; D006801:Humans; D008297:Male; D013058:Mass Spectrometry / Q000379:methods*; D008875:Middle Aged; D015203:Reproducibility of Results; D012463:Saliva / Q000737:chemistry*; D012680:Sensitivity and Specificity; D014280:Triglycerides / Q000008:administration & dosage / Q000032:analysis*; D016482:Urinalysis / Q000379:methods*
D002250:Carbon Radioisotopes; D004041:Dietary Fats; D014280:Triglycerides; D003903:Deuterium