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

Variation in milk fat globule size and composition: A source of bioactives for human health

Milk fat globules (MFGs) are secreted from the mammalian gland and are composed of a triacylglycerol core surrounded by a triple membrane structure, the milk fat globule membrane (MFGM). The MFGM contains complex lipids and proteins reported to have nutritional, immunological, neurological and digestive functions. Human and ruminant milk are shown to share a similar MFG structure but with different size, profile and abundance of protein and polar lipids. This review summarizes the reported data on human, bovine, caprine and ovine MFG composition and concentration of bioactive components in different MFG-size fractions. A comprehensive understanding of compositional variations between milk from different species and MFG size fractions may help promote various milk sources as targeted supplements to improve human development and health. MFG size and MFGM composition are species-specific and affected by lactation, diet and breed (or maternal origin). Purification and enrichment methods for some bioactive proteins and lipids present in the MFGM have yet to be established or are not scaled sufficiently to be used to supplement human diets. To overcome this problem, MFG size selection through fractionation or herd selection may provide a convenient way to pre-enrich the MFG fraction with specific protein and lipid components to fulfill human dietary and health requirements.

Lipid Composition, Digestion, and Absorption Differences among Neonatal Feeding Strategies: Potential Implications for Intestinal Inflammation in Preterm Infants

Necrotizing enterocolitis (NEC) is a significant cause of morbidity and mortality in the neonatal population. Formula feeding is among the many risk factors for developing the condition, a practice often required in the cohort most often afflicted with NEC, preterm infants. While the virtues of many bioactive components of breast milk have been extolled, the ability to digest and assimilate the nutritional components of breast milk is often overlooked. The structure of formula differs from that of breast milk, both in lipid composition and chemical configuration. In addition, formula lacks a critical digestive enzyme produced by the mammary gland, bile salt-stimulated lipase (BSSL). The gastrointestinal system of premature infants is often incapable of secreting sufficient pancreatic enzymes for fat digestion, and pasteurization of donor milk (DM) has been shown to inactivate BSSL, among other important compounds. Incompletely digested lipids may oxidize and accumulate in the distal gut. These lipid fragments are thought to induce intestinal inflammation in the neonate, potentially hastening the development of diseases such as NEC. In this review, differences in breast milk, pasteurized DM, and formula lipids are highlighted, with a focus on the ability of those lipids to be digested and subsequently absorbed by neonates, especially those born prematurely and at risk for NEC.

Bile salt-dependent lipase promotes the barrier integrity of Caco-2 cells by activating Wnt/β-catenin signaling via LRP6 receptor

Bile salt-dependent lipase (BSDL) within intestinal lumen can be endocytosed by enterocytes and support the intestinal barrier function. However, the epithelial-supporting effect of this protein has not been verified in a human cell line and neither the direct signaling pathway nor the function of endocytosis in this process has been clearly identified. We sought to investigate the signaling pathway and the membrane receptor through which BSDL might exert these effects using intestinal epithelial cells. Caco-2 cells were treated with recombinant BSDL, and the barrier function, cell proliferation, and activation of the Wnt signaling pathway were assessed. The effect of Wnt signaling activation induced by BSDL and BSDL endocytosis was investigated in LRP6-silenced and non-silenced cells. Moreover, caveolae- and clathrin-dependent endocytosis inhibitors were also applied respectively to analyze their effects on Wnt signaling activation induced by BSDL. BSDL treatment increased the barrier function but not proliferation of Caco-2 cells. It also induced β-catenin nuclear translocation and activated Wnt target gene transcription. Moreover, in the Wnt pathway, BSDL increased the levels of non-phosphorylated-β-catenin (Ser33/37/Thr41) and phosphorylated-β-catenin (Ser552). Notably, the silencing of LRP6 expression impaired BSDL endocytosis and decreased BSDL-induced β-catenin nuclear translocation. The inhibition of BSDL endocytosis induced by caveolae-mediated endocytosis inhibitor was stronger than that by clathrin-mediated endocytosis inhibitor, and the Wnt signaling activation associated with its endocytosis was also most likely caveolae-dependent. Our findings suggested that LRP6, a canonical Wnt pathway co-receptor, can mediate BSDL endocytosis and then activate Wnt signaling in Caco-2 cells.

Maltodextrin-induced intestinal injury in a neonatal mouse model

Prematurity and enteral feedings are major risk factors for intestinal injury leading to necrotizing enterocolitis (NEC). An immature digestive system can lead to maldigestion of macronutrients and increased vulnerability to intestinal injury. The aim of this study was to test in neonatal mice the effect of maltodextrin, a complex carbohydrate, on the risk of intestinal injury. The goal was to develop a robust and highly reproducible murine model of intestinal injury that allows insight into the pathogenesis and therapeutic interventions of nutrient-driven intestinal injury. Five- to 6-day-old C57BL/6 mice were assigned to the following groups: dam fed (D); D+hypoxia+Klebsiella pneumoniae; maltodextrin-dominant human infant formula (M) only; M+hypoxia; and M+hypoxia+K. pneumoniae. The mice in all M groups were gavage fed five times a day for 4 days. Mice were exposed to hypoxia twice a day for 10 min prior to the first and last feedings, and K. pneumoniae was added to feedings as per group assignment. Mice in all M groups demonstrated reduced body weight, increased small intestinal dilatation and increased intestinal injury scores. Maltodextrin-dominant infant formula with hypoxia led to intestinal injury in neonatal mice accompanied by loss of villi, increased MUC2 production, altered expression of tight junction proteins, enhanced intestinal permeability, increased cell death and higher levels of intestinal inflammatory mediators. This robust and highly reproducible model allows for further interrogation of the effects of nutrients on pathogenic factors leading to intestinal injury and NEC in preterm infants.This article has an associated First Person interview with the first author of the paper.

Fat supplementation of human milk for promoting growth in preterm infants

BACKGROUND

As preterm infants do not experience the nutrient accretion and rapid growth phase of the third trimester of pregnancy, they are vulnerable to postnatal nutritional deficits, including of fat. Consequently, they require higher fat intakes compared to their full term counterparts to achieve adequate growth and development. Human milk fat provides the major energy needs of the preterm infant and also contributes to several metabolic and physiological functions. Although human milk has many benefits for this population, its fat content is highly variable and may be inadequate for their optimum growth and development. This is a 2020 update of a Cochrane Review last published in 2000.

OBJECTIVES

To determine whether supplementation of human milk with fat compared with unsupplemented human milk fed to preterm infants improves growth, body composition, cardio-metabolic, and neurodevelopmental outcomes without significant adverse effects.

SEARCH METHODS

We used the standard search strategy of Cochrane Neonatal to search Cochrane Central Register of Controlled Trials (CENTRAL 2019, Issue 8) in the Cochrane Library and MEDLINE via PubMed on 23 August 2019. We also searched clinical trials databases and the reference lists of retrieved articles for randomised controlled trials and quasi-randomised trials.

SELECTION CRITERIA

Published and unpublished randomised controlled trials were eligible if they used random or quasi-random methods to allocate preterm infants fed human milk in hospital to supplementation or no supplementation with additional fat.

DATA COLLECTION AND ANALYSIS

No new randomised controlled trials matching the selection criteria were found but we extracted data from the previously included trial due to changes in review outcomes from when the protocol was first published. Two reviewers independently abstracted data, assessed trial quality, and the quality of evidence at the outcome level using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) criteria. We planned to perform meta-analyses using risk ratio (RR) for dichotomous data and mean difference (MD) for continuous data, with their respective 95% confidence intervals (CIs). We planned to use a fixed-effect model and to explore potential causes of heterogeneity via sensitivity analyses.

MAIN RESULTS

One randomised trial involving 14 preterm infants was included. There was no evidence of a clear difference between the fat-supplemented and unsupplemented groups in in-hospital rates of growth in weight (MD 0.6 g/kg/day, 95% CI -2.4 to 3.6; 1 RCT, n = 14 infants, very low-quality evidence), length (MD 0.1 cm/week, 95% CI -0.08 to 0.3; 1 RCT, n = 14 infants, very low-quality evidence) and head circumference (MD 0.2 cm/week, 95% CI -0.07 to 0.4; 1 RCT n = 14 infants, very low-quality evidence). There was no clear evidence that fat supplementation increased the risk of feeding intolerance (RR 3.0, 95% CI 0.1 to 64.3; 1 RCT, n = 16 infants, very low-quality evidence). No data were available regarding the effects of fat supplementation on long-term growth, body mass index, body composition, neurodevelopmental, or cardio-metabolic outcomes.

AUTHORS' CONCLUSIONS

The one included trial suggests no evidence of an effect of fat supplementation of human milk on short-term growth and feeding intolerance in preterm infants. However, the very low-quality evidence, small sample size, few events, and low precision diminishes our confidence that these results reflect the true effect of fat supplementation of human milk in preterm infants, and no long-term outcomes were reported. Further high-quality research should evaluate the effect on short and long-term growth, neurodevelopmental and cardio-metabolic outcomes in the context of the development of multicomponent fortifiers. Optimal dosage, adverse effects, and delivery practices should also be evaluated.

Fat composition in infant formula contributes to the severity of necrotising enterocolitis

Necrotising enterocolitis (NEC) is a devastating disease that typically affects formula-fed premature infants, suggesting that dietary components may influence disease pathogenesis. TAG are the major fat components of infant formula, and their digestion requires pancreatic lipases, which may be naturally deficient in premature neonates. We hypothesise that NEC develops partly from the accumulation of incompletely digested long-chain TAG-containing unsaturated fatty acids within the intestinal epithelial cells, leading to oxidative stress and enterocyte damage. We further hypothesise that the administration of a formula that contains reduced TAG ('pre-digested fat') that do not require lipase action may reduce NEC severity. To test these hypotheses, we induced NEC in neonatal mice using three different fat formulations, namely 'standard fat', 'pre-digested fat' or 'very low fat', and determined that mice fed 'standard fat' developed severe NEC, which was significantly reduced in mice fed 'pre-digested fat' or 'very low fat'. The expression level of the critical fat-digesting enzyme carboxyl ester lipase was significantly lower in the newborn compared with older pups, leading to impaired fat digestion. The accumulation of mal-digested fat resulted in the significant accumulation of fat droplets within the intestinal epithelium of the distal ileum, resulting in the generation of reactive oxygen species and intestinal inflammation. Strikingly, these changes were prevented in pups fed 'pre-digested fat' or 'very low fat' formulas. These findings suggest that nutritional formula containing a pre-digested fat system may overcome the natural lipase deficiency of the premature gut, and serve as a novel approach to prevent NEC.

Fat supplementation of human milk for promoting growth in preterm infants

BACKGROUND

As preterm infants do not experience the nutrient accretion and rapid growth phase of the third trimester of pregnancy, they are vulnerable to postnatal nutritional deficits, including of fat. Consequently, they require higher fat intakes compared to their full term counterparts to achieve adequate growth and development. Human milk fat provides the major energy needs of the preterm infant and also contributes to several metabolic and physiological functions. Although human milk has many benefits for this population, its fat content is highly variable and may be inadequate for their optimum growth and development. This is a 2018 update of a Cochrane Review last published in 2000.

OBJECTIVES

To determine whether supplementation of human milk with fat compared with unsupplemented human milk fed to preterm infants improves growth, body composition, cardio-metabolic, and neurodevelopmental outcomes without significant adverse effects.

SEARCH METHODS

We used the standard search strategy of Cochrane Neonatal to search the Cochrane Central Register of Controlled Trials (CENTRAL 2018, Issue 1), MEDLINE via PubMed (1966 to 08 February 2018), Embase (1980 to 08 February 2018), and CINAHL (1982 to 08 February 2018). We also searched clinical trials databases, conference proceedings, and the reference lists of retrieved articles for randomised controlled trials and quasi-randomised trials.

SELECTION CRITERIA

Published and unpublished randomised controlled trials were eligible if they used random or quasi-random methods to allocate preterm infants fed human milk in hospital to supplementation or no supplementation with additional fat.

DATA COLLECTION AND ANALYSIS

No new randomised controlled trials matching the selection criteria were found but we extracted data from the previously included trial due to changes in review outcomes from when the protocol was first published. Two reviewers independently abstracted data, assessed trial quality, and the quality of evidence at the outcome level using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) criteria. We planned to perform meta-analyses using risk ratio (RR) for dichotomous data and mean difference (MD) for continuous data, with their respective 95% confidence intervals (CIs). We planned to use a fixed-effect model and to explore potential causes of heterogeneity via sensitivity analyses.

MAIN RESULTS

One randomised trial involving 14 preterm infants was included. There was no evidence of a clear difference between the fat-supplemented and unsupplemented groups in in-hospital rates of growth in weight (MD 0.6 g/kg/day, 95% CI -2.4 to 3.6; 1 RCT, n = 14 infants, very low-quality evidence), length (MD 0.1 cm/week, 95% CI -0.08 to 0.3; 1 RCT, n = 14 infants, very low-quality evidence) and head circumference (MD 0.2 cm/week, 95% CI -0.07 to 0.4; 1 RCT n = 14 infants, very low-quality evidence). There was no clear evidence that fat supplementation increased the risk of feeding intolerance (RR 3.0, 95% CI 0.1 to 64.3; 1 RCT, n = 16 infants, very low-quality evidence). No data were available regarding the effects of fat supplementation on long-term growth, body mass index, body composition, neurodevelopmental, or cardio-metabolic outcomes.

AUTHORS' CONCLUSIONS

The one included trial suggests no evidence of an effect of fat supplementation of human milk on short-term growth and feeding intolerance in preterm infants. However, the very low-quality evidence, small sample size, few events, and low precision diminishes our confidence that these results reflect the true effect of fat supplementation of human milk in preterm infants, and no long-term outcomes were reported. Further high-quality research should evaluate the effect on short and long-term growth, neurodevelopmental and cardio-metabolic outcomes in the context of the development of multicomponent fortifiers. Optimal dosage, adverse effects, and delivery practices should also be evaluated.

Bile salt dependent lipase promotes intestinal adaptation in rats with massive small bowel resection

Intestinal adaptation is important for the short bowel syndrome (SBS) patients. Growing evidence has suggested that bile salt dependent lipase (BSDL) not only has the lipolytic activity, but also the immune-modulating and pro-proliferative activities. The purpose of the present study was to investigate the effects of BSDL on intestinal adaptive growth and gut barrier function in a rat model of SBS. Twenty-four male Sprague-Dawley rats were randomly divided into three experimental groups: sham group (rats underwent bowel transection and re-anastomosis), SBS group (rats underwent 80% bowel resection), SBS-BSDL group (SBS rats orally administered BSDL). The animals were weighed daily. The intestinal morpho-histochemical changes and intestinal barrier function were determined 14 days after the operations. Meanwhile, the expressions of Wnt signaling molecules in enterocytes were also analyzed by immunohistochemistry and Western blot. The postoperative weight gain was faster in the SBS rats treated with BSDL than in the SBS/untreated group. The SBS rats treated with BSDL had significantly greater villus height, crypt depth, and enterocyte proliferation in their residual intestines, as compared with the SBS/untreated group. The recovery of intestinal barrier function was promoted and the expressions of tight-junction proteins were increased in the SBS rats treated with BSDL. Additionally, the data indicated that the proadaptive activities of BSDL might be mediated by Wnt signaling activation in the enterocytes. These observations suggested that enteral BSDL administration promoted intestinal adaptive growth and barrier repairing by activating Wnt signaling pathway in SBS rats.

Pancreatic adenocarcinoma, chronic pancreatitis, and MODY-8 diabetes: is bile salt-dependent lipase (or carboxyl ester lipase) at the crossroads of pancreatic pathologies?

Pancreatic adenocarcinomas and diabetes mellitus are responsible for the deaths of around two million people each year worldwide. Patients with chronic pancreatitis do not die directly of this disease, except where the pathology is hereditary. Much current literature supports the involvement of bile salt-dependent lipase (BSDL), also known as carboxyl ester lipase (CEL), in the pathophysiology of these pancreatic diseases. The purpose of this review is to shed light on connections between chronic pancreatitis, diabetes, and pancreatic adenocarcinomas by gaining an insight into BSDL and its variants. This enzyme is normally secreted by the exocrine pancreas, and is diverted within the intestinal lumen to participate in the hydrolysis of dietary lipids. However, BSDL is also expressed by other cells and tissues, where it participates in lipid homeostasis. Variants of BSDL resulting from germline and/or somatic mutations (nucleotide insertion/deletion or nonallelic homologous recombination) are expressed in the pancreas of patients with pancreatic pathologies such as chronic pancreatitis, MODY-8, and pancreatic adenocarcinomas. We discuss the possible link between the expression of BSDL variants and these dramatic pancreatic pathologies, putting forward the suggestion that BSDL and its variants are implicated in the cell lipid metabolism/reprogramming that leads to the dyslipidemia observed in chronic pancreatitis, MODY-8, and pancreatic adenocarcinomas. We also propose potential strategies for translation to therapeutic applications.

Purification and characterization of recombinant human bile salt-stimulated lipase expressed in milk of transgenic cloned cows

Bile salt-stimulated lipase (BSSL) is a lipolytic digestive enzyme with broad substrate specificity secreted from exocrine pancreas into the intestinal lumen in all species and from the lactating mammary gland into the milk of some species, notably humans but not cows. BSSL in breast milk facilitates digestion and absorption of milk fat and promotes growth of small for gestational age preterm infants. Thus, purified recombinant human BSSL (rhBSSL) can be used for treatment of patients with fat malabsorption and expressing rhBSSL in the milk of transgenic cloned cows would therefore be a mean to meet a medical need. In the present study, a vector pBAC-hLF-hBSSL was constructed, which efficiently expressed active rhBSSL in milk of transgenic cloned cows to a concentration of 9.8 mg/ml. The rhBSSL purified from cow milk had the same enzymatic activity, N-terminal amino acid sequence, amino acid composition and isoelectric point and similar physicochemical characteristics as human native BSSL. Our study supports the use of transgenic cattle for the cost-competitive, large-scale production of therapeutic rhBSSL.

Specificity of infant digestive conditions: some clues for developing relevant in vitro models

Digestion of nutrients is an essential function of the newborn infant gut to allow growth and development and understanding infant digestive function is essential to optimize nutrition and oral drug delivery. Ethical considerations prohibit invasive in vivo trials and as a consequence in vitro assays are often conducted. However, the choice of in vitro model parameters are not supported by an exhaustive analysis of the literature and do not mimic precisely the digestive conditions of the infant. This review contains a compilation of the studies which characterized the gastroduodenal conditions in full-term or preterm infants of variable postnatal age from birth up to six months. Important data about healthy full-term infants are reported. The enzymatic (type of enzymes and level of activity) and nonenzymatic (milk-based diet, frequency of feeding, bile salt concentrations) conditions of digestion in infants are shown to differ significantly from those in adults. In addition, the interindividual and developmental variability of the digestive conditions in infants is also highlighted.

rhBSSL improves growth and LCPUFA absorption in preterm infants fed formula or pasteurized breast milk

OBJECTIVES

Preterm infants often experience suboptimal growth, which can affect organ development. The aim of this study was to improve growth by treatment with bile salt-stimulated lipase (BSSL), naturally present in breast milk, but lost after pasteurization, and absent in formula.

METHODS

Two clinical trials were performed with a predefined analysis of combined data to investigate the effects of recombinant human BSSL (rhBSSL) treatment on growth velocity and fat absorption in preterm infants. The studies were randomized and double-blinded comparing 7-day treatment with rhBSSL and placebo, administered in pasteurized breast milk or formula, using a crossover design.

RESULTS

Sixty-three infants were evaluated for safety. At randomization, the mean (standard deviation) weight was 1467 (193) g and mean postmenstrual age was 32.6 (0.5) weeks. Sixty and 46 infants were evaluated for growth velocity and fat absorption, respectively. rhBSSL treatment significantly improved mean growth velocity by 2.93 g · kg · day (P<0.001) compared with placebo (mean 16.86 vs 13.93 g · kg · day) and significantly decreased the risk of suboptimal growth (<15 g · kg · day) (30% vs 52%, P=0.004). rhBSSL significantly increased absorption of the long-chain polyunsaturated fatty acids, docosahexaenoic acid, and arachidonic acid by 5.76% (P=0.013) and 8.55% (P=0.001), respectively, but had no significant effect on total fat absorption. The adverse-event profile was similar to placebo.

CONCLUSIONS

In preterm infants fed pasteurized breast milk or formula, 1 week of treatment with rhBSSL was well tolerated and significantly improved growth and long-chain polyunsaturated fatty acid absorption compared to placebo. This publication presents the first data regarding the use of rhBSSL in preterms and the results have led to further clinical studies.

Bile salt-stimulated lipase plays an unexpected role in arthritis development in rodents

OBJECTIVE

The present study aimed to explore the hypothesis that bile salt-stimulated lipase (BSSL), in addition to being a key enzyme in dietary fat digestion during early infancy, plays an important role in inflammation, notably arthritis.

METHODS

Collagen-induced arthritis (CIA) and pristane-induced arthritis (PIA) in rodents are commonly used experimental models that reproduce many of the pathogenic mechanisms of human rheumatoid arthritis, i.e. increased cellular infiltration, synovial hyperplasia, pannus formation, and erosion of cartilage and bone in the distal joints. We used the CIA model to compare the response in BSSL wild type (BSSL-WT) mice with BSSL-deficient 'knock-out' (BSSL-KO) and BSSL-heterozygous (BSSL-HET) littermates. We also investigated if intraperitoneal injection of BSSL-neutralizing antibodies affected the development or severity of CIA and PIA in mice and rats, respectively.

RESULTS

In two consecutive studies, we found that BSSL-KO male mice, in contrast to BSSL-WT littermates, were significantly protected from developing arthritis. We also found that BSSL-HET mice were less prone to develop disease compared to BSSL-WT mice, but not as resistant as BSSL-KO mice, suggesting a gene-dose effect. Moreover, we found that BSSL-neutralizing antibody injection reduced both the incidence and severity of CIA and PIA in rodents.

CONCLUSION

Our data strongly support BSSL as a key player in the inflammatory process, at least in rodents. It also suggests the possibility that BSSL-neutralizing agents could serve as a therapeutic model to reduce the inflammatory response in humans.

Comparative Structures and Evolution of Vertebrate Carboxyl Ester Lipase (CEL) Genes and Proteins with a Major Role in Reverse Cholesterol Transport

Bile-salt activated carboxylic ester lipase (CEL) is a major triglyceride, cholesterol ester and vitamin ester hydrolytic enzyme contained within pancreatic and lactating mammary gland secretions. Bioinformatic methods were used to predict the amino acid sequences, secondary and tertiary structures and gene locations for CEL genes, and encoded proteins using data from several vertebrate genome projects. A proline-rich and O-glycosylated 11-amino acid C-terminal repeat sequence (VNTR) previously reported for human and other higher primate CEL proteins was also observed for other eutherian mammalian CEL sequences examined. In contrast, opossum CEL contained a single C-terminal copy of this sequence whereas CEL proteins from platypus, chicken, lizard, frog and several fish species lacked the VNTR sequence. Vertebrate CEL genes contained 11 coding exons. Evidence is presented for tandem duplicated CEL genes for the zebrafish genome. Vertebrate CEL protein subunits shared 53-97% sequence identities; demonstrated sequence alignments and identities for key CEL amino acid residues; and conservation of predicted secondary and tertiary structures with those previously reported for human CEL. Phylogenetic analyses demonstrated the relationships and potential evolutionary origins of the vertebrate CEL family of genes which were related to a nematode carboxylesterase (CES) gene and five mammalian CES gene families.

BSSL and PLRP2: key enzymes for lipid digestion in the newborn examined using the Caco-2 cell line

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.

Carboxyl ester lipase from either mother's milk or the pancreas is required for efficient dietary triglyceride digestion in suckling mice

Because dietary fats provide an important source of energy in the newborn, the efficient digestion of dietary fats is critical to their well-being. Despite the importance of dietary fat digestion, newborns have a deficiency of pancreatic triglyceride lipase, the predominant digestive lipase in adults. The efficient dietary fat digestion in newborns suggests that other lipases must compensate for the lack of pancreatic triglyceride lipase. In this study, we test the hypothesis that breast milk, pancreatic carboxyl ester lipase (CEL), or both contribute to dietary fat digestion in the newborn. To test this hypothesis, we determined the amount and composition of fecal fat in wild-type and CEL-deficient newborns nursed by either wild-type or CEL-deficient dams. We tested all genetic permutations of the nursing pairs. An interaction between the genotype of the dam and of the pup determined the amount of fecal fat (P < 0.001). Fecal fat was highest in CEL-deficient pups nursed by CEL-deficient dams. Furthermore, only the feces from the CEL-deficient pups nursed by CEL-deficient dams contained undigested lipids. Even with increased fecal fats, the CEL-deficient pups had normal weight gain. Our results demonstrate that CEL contributes significantly to dietary triglyceride digestion whether it originates from mother's milk or pancreatic secretions. However, only the absence of both mother's milk and pancreatic CEL produces fat maldigestion. The absence of a single CEL source makes no difference in the efficiency of dietary fat absorption.

Bile salt-stimulated lipase and pancreatic lipase-related protein 2 are the dominating lipases in neonatal fat digestion in mice and rats

During infancy, the basic conditions for digestion of dietary fat differ from later in life. The bile salt-stimulated lipase (BSSL) is an enzyme expressed in the exocrine pancreas and in some species (including human) also in the lactating mammary gland and secreted with the milk. The aim of this study was to compare the ontogeny of four pancreatic lipases [BSSL, pancreatic triglyceride lipase (PL), pancreatic lipase-related protein 2 (PLRP2), and phospholipase A2 (PLA2)] in one species that supplies BSSL with milk (the mouse) and one that does not (the rat). We followed expression of the four pancreatic lipases from postnatal d 1 until after weaning in both species. We found that BSSL and PLRP2, two lipases with broad substrate specificity, dominated. It was not until weaning that significant expression of PL and PLA2 were induced. Thus, BSSL and PLRP2 seem to be responsible for fat digestion as long as milk is the main food. Moreover, the early temporal pattern of BSSL expression differed between species. We speculate that the milk-borne BSSL is able to compensate for a slower ontogeny of pancreatic BSSL expression in the mouse.

Human pancreatic digestive enzymes

A primary function of the pancreas is to produce digestive enzymes that are delivered to the small intestine for the hydrolysis of complex nutrients. Much of our understanding of digestive enzymes comes from studies in animals. New technologies and the availability of the sequence of the human genome allow for a critical review of older reports and assumptions based on animal studies. This report updates our understanding of human pancreatic digestive enzymes with a focus on new insights into the biology of human proteases, lipases and amylases.

Crystal structure of the catalytic domain of human bile salt activated lipase

Bile-salt activated lipase (BAL) is a pancreatic enzyme that digests a variety of lipids in the small intestine. A distinct property of BAL is its dependency on bile salts in hydrolyzing substrates of long acyl chains or bulky alcoholic motifs. A crystal structure of the catalytic domain of human BAL (residues 1-538) with two surface mutations (N186D and A298D), which were introduced in attempting to facilitate crystallization, has been determined at 2.3 A resolution. The crystal form belongs to space group P2(1)2(1)2(1) with one monomer per asymmetric unit, and the protein shows an alpha/beta hydrolase fold. In the absence of bound bile salt molecules, the protein possesses a preformed catalytic triad and a functional oxyanion hole. Several surface loops around the active site are mobile, including two loops potentially involved in substrate binding (residues 115-125 and 270-285).