Carboxyl ester lipase activity in milk prevents fat-derived intestinal injury in neonatal mice

Abstract

Carboxyl ester lipase (bile salt-stimulated lipase) is a pancreatic enzyme capable of hydrolyzing esters of cholesterol and fat-soluble vitamins. It also efficiently digests triglycerides (TG) into free fatty acids and glycerol and is abundant in the milk of humans and several other species. We used the mouse as a model to test the hypothesis that milk-derived carboxyl ester lipase (CEL) digests milk TG and that without its activity milk lipids and their digestion intermediates can disrupt the intestinal epithelium of neonates. CEL protein and enzymatic activity were shown to be abundant in mouse milk. After 24-h administration of the CEL-specific inhibitor, WAY-121,751-5, the small intestines of treated and control neonates were analyzed histologically for signs of fat malabsorption and injury to their villus epithelium. In vehicle-fed controls, TG were digested and absorbed in the duodenum and jejunum, whereas, in inhibitor-fed littermates, large intracellular neutral lipid droplets accumulated in enterocytes of the ileum, resulting in damage to the villus epithelium. Similar results were observed in neonates nursed by CEL knockout females compared with heterozygous controls. The results suggest that lack of CEL activity causes incomplete digestion of milk fat and lipid accumulation by enterocytes in the ileum of neonatal mice.

Fig. 1

Western blot of whey proteins from mouse milk. Lanes 1 and 2 show milk samples from two different female mice transferred to nitrocellulose, reacted with antibodies against carboxyl ester lipase (CEL), and detected with ¹²⁵I-labeled secondary antibody.

Fig. 2

Representative histopathology of small intestines from control and treated mice. A-F: hematoxylin and eosin (H&E)-stained sections of paraffin-embedded tissues from 4-day-old pups. G-L: oil red O-stained sections of frozen specimens from 8-day-old pups. A-C and G-I are from control animals, and D-F and J-L are from inhibitor-treated animals. A, D, G, and J are duodenum; B, E, H, and K are jejunum; C, F, I, and L are ileum. Arrowheads in F indicate areas of apparent disruption of villus epithelium in ileum from inhibitor-treated pups. Bars in A-F = 100 µm. Original magnification, × 66 for G, H, I, J, and L and × 50 for K.

Fig. 3

Representative histopathology of jejunoileal segments of intestines from 6- to 7-day-old pups nursed by CEL heterozygous females (A and C) or CEL knockout females (B and D). A and B: H&E-stained paraffin sections. C and D: oil red O-stained frozen sections. Bars = 100 µm. Pups were CEL heterozygous in A and C and CEL knockout in B and D.