Gastric lipase and other lipolytic enzymes activity in the preterm infant fed raw, pasteurized or pasteurized-homogenized human milk
Résumé
-Objectives and study: Hydrolysis of milk lipids is an essential step in their digestion, initiated in the
digestive tract by human gastric lipase (HGL). Although limited, gastric lipolysis has been presented
very early as a key phenomenon in efficient fat digestion for newborns. It compensates for the
immaturity of exocrine pancreatic function and favours the subsequent action of other lipolytic
enzymes such as pancreatic or bile salt dependant lipases (HPL and BSSL, respectively). Some values
of 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 formula
versus human milk), the age of the infant or the analysis method. However, in these studies the HGL
output has never been estimated after administration of various types of human milk, nor the
potential contribution of non-gastric lipolytic enzymes. The objective of the present study is thus to
determine HGL activity, output and the contribution of other lipolytic enzymes in gastric aspirates of
preterm infants in fasting state or after administration of raw, pasteurized or pasteurizedhomogenized
human milk.
-Methods: In vivo study was conducted at Rennes Hospital on preterm infants fed by nasogastric
tube (NCT02112331). The infants were included in two independent groups determining the type of
meals: A) raw and pasteurized human milk; B) pasteurized and pasteurized-homogenized human
milk. After collection (twice a day, six-day sequence), aspirates were immediately blended with
glycerol (50:50 v/v) and frozen. Fasted gastric contents were collected three hours after last meal (up
to 12 times per patient to verify intra-individual variation) and postprandial digesta at 35, 60 or 90
min after administrated meal. Gastric volume and pH decrease were monitored. Lipolytic activity was
assessed 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-gastric
lipases contribution.
-Results: Results evidenced high inter and intra-individual variability on estimated gastric lipolytic
activities. In the group A (n=12), lipolytic activity measured at pH 6 ranged from 2 up to 100 U/mL of
fasting gastric content. The determination at pH 8 revealed a contribution of non-gastric lipases
activity ranging between 0 and 61%: as HGL is not active at such pH, a remaining activity will thus
indicate the presence of BSSL or HPL. These contributions were higher in patients fed raw compared
to pasteurized human milk in both fasted and postprandial states, probably indicating: i) active BSSL
from residual raw human milk contributed to gastric activity even three hours after meal; ii) the
presence of HPL (and hence intestinal content) in the stomach, which confirms the immaturity of
motility function in preterms. In patients fed with pasteurized milk the lipolytic activity increased
with postprandial time, indicating a HGL secretion induced by the meal. Lipolytic activities from
group 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 infant
digestion and analyze the link between gastric lipolytic activity and lipid digestion.