Background & aims: Experimental (nutritional) interventions in preterm infants frequently focus on intestinal maturation, as improving tolerance to enteral nutrition is a major goal. Intestinal permeability and lactase activity serve as markers for intestinal maturation. We aimed to develop a protocol for the simultaneous assessment of both markers in human-milk-fed preterm infants by a sugar absorption test. In addition, we developed a new gas chromatography-mass spectrometry (GC-MS) method for the analysis of lactulose, lactose, and mannitol in urine and milk collected during the sugar absorption test.
Methods: The sugar absorption test was performed on days 4, 7, and 14 postpartum in 12 preterm infants (gestational age of 26-32 weeks). Human milk was collected, pooled, and divided into equal portions to provide a stable lactose intake for 24 h. Urine was collected in the last 6 h of this 24 h period, after administration of a bolus test sugar solution. Samples were analyzed by GC-MS after derivatization by oxime formation combined with acetylation.
Results: The GC-MS method was validated and used for the accurate measurement of lactulose, lactose, and mannitol concentrations. The urinary lactulose/mannitol ratio declined with time, suggesting a decreased intestinal permeability. The urine-to-milk-lactulose/lactose ratio increased as a result of increased lactase activity with time.
Conclusions: The developed protocol for simultaneous assessment of intestinal permeability and lactase activity can be used to monitor the effect of experimental (nutritional) interventions in human-milk-fed preterm infants. Urine and milk samples obtained during the sugar absorption test can be accurately analyzed by GC-MS.
Keywords: Gas chromatography; Intestinal maturation; Lactose; Lactulose; Mannitol; Mass spectrometry.
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