Gastric lipase and other lipolytic enzymes activity in the preterm infant fed raw, pasteurized or pasteurized-homogenized human milk

Hydrolysis of milk lipids is initiated in the digestive tract by human gastric lipase (HGL). Though only qualitative, gastric lipolysis has been presented as a key phenomenon in newborn fat digestion. The aim of this study was to determine HGL activity, output and the contribution of other lipolytic enzymes in the gastric aspirates of preterm infants in fasting state or after administration of either raw, or pasteurized or pasteurized-homogenized human milks (RHM, PHM, PHHM, respectively).In vivo study was conducted at Rennes Hospital on preterm infants fed by nasogastric tube (NCT02112331), included in two independent groups determining the type of meals: A) RHM and PHM; B) PHM and PHHM. Over a six-day sequence, gastric aspirates were collected twice a day, before and at 35, 60 or 90 min after the start of ingestion. Lipolytic activity was determined by titration of released free fatty acids from tributyrin (pH-stat technique, at pH 4.5, 6 and 8, at 37°C). Gastric pH and volume were monitored. In fasted state (n = 20 infants), the average HGL concentration was 61.7 ± 0.01 µg/mL and the global lipolytic activity detected at pH 4.5 averaged 17.5 ± 2.9 U/mL/kg. Results revealed a contribution of non-gastric lipases in the fasting state, indicating the presence of bile salt stimulated lipase (BSSL) or, in few aspirates, of pancreatic lipase. Postprandial lipolytic activity increased with time, indicating that meal induced HGL secretion. In group A, it was higher after administration of RHM compared to PHM (n = 5), disregarding the postprandial time (respectively 17.1 ± 0.0 and 8.0 ± 0.0 U/mL/kg at 90 min, p < 0.05). In group B, homogenization had no effect on postprandial lipolytic activity (n = 4), with an average of 12.9 ± 0.0 U/mL/kg at 90 min. Results were compared with available literature data on lipase activity and lipolysis level.The influence of RHM administration suggests that, in addition to conveying additional activity via its content in BSSL, this milk may enhance gastric secretions as compared to PHM. 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.