Abstract
In rodents, bile salt-stimulated lipase (BSSL) and pancreatic lipase-related protein 2 (PLRP2) are the dominant lipases expressed in the exocrine pancreas in early life when milk is the main food. The aim of the present study was to evaluate whether BSSL and PLRP2 are also key enzymes in neonatal intestinal fat digestion. Using Caco-2 cells as a model for the small intestinal epithelium, purified human enzymes were incubated in the apical compartment with substrates, bile salt composition and concentrations physiologic to newborn infants. Both BSSL and PLRP2 hydrolyzed triglycerides (TG) to free FA and glycerol. Released FA were absorbed by the cells and reesterfied to TG. Together, BSSL and PLRP2 had a synergistic effect, increasing cellular uptake and reesterification 4-fold compared with the sum of each lipase alone. A synergistic effect was also observed with retinyl ester as a substrate. PLRP2 hydrolyzed cholesteryl ester but not as efficiently as BSSL, and the two had an additive rather than synergistic effect. We conclude the key enzymes in intestinal fat digestion are different in newborns than later in life. Further studies are needed to fully understand this difference and its implication for designing optimal neonatal nutrition.
Highlights
In rodents, bile salt-stimulated lipase (BSSL) and pancreatic lipase-related protein 2 (PLRP2) are the dominant lipases expressed in the exocrine pancreas in early life when milk is the main food
In the present study, using in vitro conditions aiming at resembling physiologic conditions of the newborn infant with respect to pH, bile salt composition and concentration, lipid substrates, enzyme concentrations, and uptake of cellular lipolysis products, we demonstrated both BSSL and PLRP2 hydrolyze TG, retinyl esters (RE), and cholesterol esters (CE)
Both have the potential to hydrolyze each TG into three FA and one glycerol rather than two FA and one sn2-MG, which is a characteristic of pancreatic triglyceride lipase (PTL)
Summary
Bile salt-stimulated lipase (BSSL) and pancreatic lipase-related protein 2 (PLRP2) are the dominant lipases expressed in the exocrine pancreas in early life when milk is the main food. Using Caco-2 cells as a model for the small intestinal epithelium, purified human enzymes were incubated in the apical compartment with substrates, bile salt composition and concentrations physiologic to newborn infants. Both BSSL and PLRP2 hydrolyzed triglycerides (TG) to free FA and glycerol. The luminal bile salt concentration during digestion reported for healthy adults is in the range 2–30 mM [2], partly depending on the composition of the meal [3] In newborn infants, this range is much lower, 1–5 mM [2, 4, 5], during established fat absorption [6]. When fed raw milk, the infants gained more weight and the kneeheal length increased more compared with when fed pasteurized milk [18]
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