Résumé
-Objectives and study: Hydrolysis of milk lipids is an essential step in their digestion, initiated in thedigestive tract by human gastric lipase (HGL). Although limited, gastric lipolysis has been presentedvery early as a key phenomenon in efficient fat digestion for newborns. It compensates for theimmaturity of exocrine pancreatic function and favours the subsequent action of other lipolyticenzymes such as pancreatic or bile salt dependant lipases (HPL and BSSL, respectively). Some valuesof HGL activity have been determined in gastric aspirates of infants in fasting state or postprandially.High variability was reported probably due to influence of the nature of the meal (infant formulaversus human milk), the age of the infant or the analysis method. However, in these studies the HGLoutput has never been estimated after administration of various types of human milk, nor thepotential contribution of non-gastric lipolytic enzymes. The objective of the present study is thus todetermine HGL activity, output and the contribution of other lipolytic enzymes in gastric aspirates ofpreterm infants in fasting state or after administration of raw, pasteurized or pasteurizedhomogenizedhuman milk.-Methods: In vivo study was conducted at Rennes Hospital on preterm infants fed by nasogastrictube (NCT02112331). The infants were included in two independent groups determining the type ofmeals: A) raw and pasteurized human milk; B) pasteurized and pasteurized-homogenized humanmilk. After collection (twice a day, six-day sequence), aspirates were immediately blended withglycerol (50:50 v/v) and frozen. Fasted gastric contents were collected three hours after last meal (upto 12 times per patient to verify intra-individual variation) and postprandial digesta at 35, 60 or 90min after administrated meal. Gastric volume and pH decrease were monitored. Lipolytic activity wasassessed by pH-stat at pH 6 (37°C) using tributyrin as substrate (as detailed by Gargouri et al., 1986),at least on triplicate. A subsequent determination at pH 8 allowed the estimation of non-gastriclipases contribution.-Results: Results evidenced high inter and intra-individual variability on estimated gastric lipolyticactivities. In the group A (n=12), lipolytic activity measured at pH 6 ranged from 2 up to 100 U/mL offasting gastric content. The determination at pH 8 revealed a contribution of non-gastric lipasesactivity ranging between 0 and 61%: as HGL is not active at such pH, a remaining activity will thusindicate the presence of BSSL or HPL. These contributions were higher in patients fed raw comparedto pasteurized human milk in both fasted and postprandial states, probably indicating: i) active BSSLfrom residual raw human milk contributed to gastric activity even three hours after meal; ii) thepresence of HPL (and hence intestinal content) in the stomach, which confirms the immaturity ofmotility function in preterms. In patients fed with pasteurized milk the lipolytic activity increasedwith postprandial time, indicating a HGL secretion induced by the meal. Lipolytic activities fromgroup B are currently been analyzed and will be further detailed.-Conclusion: This study presents a unique set of data illustrating the specificity of preterm infants’gastric digestive conditions. These data will be useful to develop relevant in vitro models of infantdigestion and analyze the link between gastric lipolytic activity and lipid digestion.