Bile salt stimulated lipase: comparative studies in ferret milk and lactating mammary gland

Identification and characterization of novel carboxyl ester lipase gene variants in patients with different subtypes of diabetes

INTRODUCTION

Mutations of CEL gene were first reported to cause a new type of maturity-onset diabetes of the young (MODY) denoted as MODY8 and then were also found in patients with type 1 (T1D) and type 2 diabetes (T2D). However, its genotype-phenotype relationship has not been fully determined and how carboxyl ester lipase (CEL) variants result in diabetes remains unclear. The aim of our study was to identify pathogenic variants of CEL in patients with diabetes and confirm their pathogenicity.

RESEARCH DESIGN AND METHODS

All five patients enrolled in our study were admitted to Shandong Provincial Hospital and diagnosed with diabetes in the past year. Whole-exome sequencing was performed to identify pathogenic variants in three patients with MODY-like diabetes, one newborn baby with T1D and one patient with atypical T2D, as well as their immediate family members. Then the consequences of the identified variants were predicted by bioinformatic analysis. Furthermore, pathogenic effects of two novel CEL variants were evaluated in HEK293 cells transfected with wild-type and mutant plasmids. Finally, we summarized all CEL gene variants recorded in Human Gene Mutation Database and analyzed the mutation distribution of CEL.

RESULTS

Five novel heterozygous variants were identified in CEL gene and they were predicted to be pathogenic by bioinformatic analysis. Moreover, in vitro studies indicated that the expression of CEL^R540C was remarkably increased, while p.G729_T739del variant did not significantly affect the expression of CEL. Both novel variants obviously abrogated the secretion of CEL. Furthermore, we summarized all reported CEL variants and found that 74.3% of missense mutations were located in exons 1, 3, 4, 10 and 11 and most missense variants clustered near catalytic triad, Arg-83 and Arg-443.

CONCLUSION

Our study identified five novel CEL variants in patients with different subtypes of diabetes, expanding the gene mutation spectrum of CEL and confirmed the pathogenicity of several novel variants.

Homozygosity of short VNTR lengths in the CEL gene may confer susceptibility to idiopathic chronic pancreatitis

OBJECTIVE

The carboxyl-ester lipase (CEL) gene contains a variable number of tandem repeats (VNTR) region. It remains unclear whether the number of repeats in the CEL VNTR is related to the risk of pancreatic diseases. The aim of this study was to investigate whether CEL VNTR length is associated with idiopathic chronic pancreatitis (ICP), alcoholic chronic pancreatitis (ACP), or pancreatic cancer in a cohort of Chinese patients.

METHODS

CEL VNTRs were genotyped in patients diagnosed with ICP (n = 771), ACP (n = 222), or pancreatic cancer (n = 263), and in healthy controls (n = 927). CEL VNTR lengths were determined using a screening method combining PCR and DNA fragment analysis.

RESULTS

Overall, the CEL VNTR lengths ranged from 5 to 22 repeats, with the 16-repeat allele ('normal' size, N) accounting for 73.82% of all observed alleles. The VNTR allele frequencies and genotype distributions were not significantly different between healthy controls and patients with ACP or pancreatic cancer. For the ICP group, allele frequencies did not differ significantly from the controls, while the frequency of the SS genotype (homozygosity for 5-15 repeats) was significantly higher in the patients (4.67%) than in the controls (1.94%) (p = 0.0014; OR = 2.47; 95% CI = 1.39-4.39).

CONCLUSIONS

There were no associations between the CEL VNTR length and ACP or pancreatic cancer. However, homozygosity for short VNTR lengths may confer susceptibility to ICP.

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.

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.

Is Frozen Human Milk That Is Refused by Mother's Own Infant Suitable for Human Milk Bank Donation?

Background: Infant refusal to feed previously frozen human milk is thought possibly attributable to lipase, an enzyme that cleaves fatty acids from milk triglycerides potentially changing the taste of the milk. Previous reports suggest that this milk is not harmful to infants; however, the lipase activity, macronutrient content, concentration of free fatty acids (FFAs), pH, and bacterial load of milk that meets this criterion are not fully understood. Objective: The objective was to determine whether refused frozen milk is different in composition from typical milk deposits received at a human milk bank. Methods: Frozen milk deposits previously refused by mother's own infant were collected from 16 mothers at five different time points when available (postpartum days 30, 60, 90, 120, and 150). Lipase activity, macronutrient composition, levels of FFA, pH, and bacteriology were determined. Analysis of mature donor milk and bacteriology data from the Ontario milk bank were used as controls. Results: The lipase activity for all samples was at or below literature values for mature human milk and lower compared with control milk (p < 0.001) for all time periods except at day 30. Macronutrient composition was not different from control values and did not change significantly over 150 days, with the exception of crude protein, which declined with milk maturity (p < 0.005). The pH for all postpartum time groups was lower (p < 0.02) in refused milk, and was inversely associated with lipase activity and FFA. FFA and bacterial counts were not different from control samples. Conclusions: Infant refusal of previously frozen milk may not be entirely due to endogenous lipase activity. This milk appears suitable for donation to human milk banks.

The role of the carboxyl ester lipase (CEL) gene in pancreatic disease

The enzyme carboxyl ester lipase (CEL), also known as bile salt-dependent or -stimulated lipase (BSDL, BSSL), hydrolyzes dietary fat, cholesteryl esters and fat-soluble vitamins in the duodenum. CEL is mainly expressed in pancreatic acinar cells and lactating mammary glands. The human CEL gene resides on chromosome 9q34.3 and contains a variable number of tandem repeats (VNTR) region that encodes a mucin-like protein tail. Although the number of normal repeats does not appear to significantly influence the risk for pancreatic disease, single-base pair deletions in the first VNTR repeat cause a syndrome of endocrine and exocrine dysfunction denoted MODY8. Hallmarks are low fecal elastase levels and pancreatic lipomatosis manifesting before the age of twenty, followed by development of diabetes and pancreatic cysts later in life. The mutant protein forms intracellular and extracellular aggregates, suggesting that MODY8 is a protein misfolding disease. Recently, a recombined allele between CEL and its pseudogene CELP was discovered. This allele (CEL-HYB) encodes a chimeric protein with impaired secretion increasing five-fold the risk for chronic pancreatitis. The CEL gene has proven to be exceptionally polymorphic due to copy number variants of the CEL-CELP locus and alterations involving the VNTR. Genome-wide association studies or deep sequencing cannot easily pick up this wealth of genetic variation. CEL is therefore an attractive candidate gene for further exploration of links to pancreatic disease.

Long-chain polyunsaturated fatty acids (LC-PUFA) during early development: contribution of milk LC-PUFA to accretion rates varies among organs

Long-chain polyunsaturated fatty acids (LC-PUFA) accretion (essential for growth and neural development) was studied from late fetal throughout weaning age in the ferret, a species with maternal LC-PUFA sufficiency during pregnancy and lactation. The data show that a) accretion rate of LC-PUFA is rapid during early postnatal development, b) milk LC-PUFA decrease during lactation, c) adipose tissue LC-PUFA level is directly related to milk LC-PUFA level, while accretion in brain and liver exceeds dietary intake, d) accretion of arachidonic acid occurs earlier than docosahexaenoic acid, suggesting earlier development of n6-fatty acid endogenous synthesis.

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

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.

Molecular cloning of the bile salt-dependent lipase of ferret lactating mammary gland: an overview of functional residues

Ferret lactating mammary gland bile salt-dependent lipase (BSDL, EC 3.1.1.-) has been cloned by RT-PCR. The open reading frame consists of 1869 nucleotides which encode 623 amino acids of the functional enzyme. When compared to other species, the greatest homology is observed between residues 1 and 484, with little or no homology at the C-terminal end where seven repeated segments of similar sequence are located. Ferret mammary gland BSDL retains residues involved in the active site and the tentative heparin binding site at similar positions in comparison to other milk or pancreatic BSDL. Other important items, such as binding peptide to chaperone molecular, phosphorylation site(s) or bile salt binding sites, were also tentatively located in well conserved regions of seven available BSDL sequences.

Gastric lipase and pepsin activities in the developing ferret: nonparallel development of the two gastric digestive enzymes

BACKGROUND

Gastric lipase has an important compensatory function in neonatal fat digestion. The activity level of pepsin and its role in protein digestion is less well understood. We have, therefore, studied the ontogeny of lipase and pepsin in the ferret, a species with a neonatal fat digestion pattern similar to that of humans.

METHODS

Gastric lipase and pepsin activities were quantified from the late fetal period throughout lactation, and were compared with those of the adult.

RESULTS

The data show earlier ontogeny and much more rapid rise of lipase activity than of pepsin. Lipase activity was present during the last week of fetal development, whereas pepsin was detected only postnatally. Lipase activity was 72.8% +/- 14.2% and 153% +/- 9.95% and pepsin activity was 11.6% +/- 1.3% and 30.1% +/- 1.3% of the adult level at 2 and 4 wk of age, respectively.

CONCLUSIONS

We conclude that lipase activity develops early and exceeds adult activity during the suckling period, when fat intake is very high. The low pepsin activity and high postprandial pH probably limit gastric proteolysis, thereby contributing to the structural and functional stability of milk proteins, many with protective or bioactive function in the gastrointestinal tract of the newborn.

Digestive enzymes in human milk: stability at suboptimal storage temperatures

BACKGROUND

Women who return to work outside of the home while still breastfeeding must often store the expressed milk at less than optimal temperatures. Human milk provides digestive enzymes (amylase and lipase) that compensate in the newborn for immature pancreatic function.

METHODS

We have assessed the stability of amylase and bile salt-dependent lipase after storage for 1-24 h at 15, 25, and 38 degrees C.

RESULTS

Both enzymes were stable at 15 and 25 degrees C for 24 h, whereas at 38 degrees C there was a 15 and 20% decrease in lipase and amylase activity, respectively. The stability of milk lipoprotein lipase was also tested. This very labile enzyme was more stable in milk than previously reported for blood and tissues, i.e., 20 and 50% decrease in activity after storage at 15 or 25 degrees C for 24 h, respectively. A two-unit drop in milk pH by 24 h of storage would not affect the activity of digestive enzymes, which are stable at pH > 3.5.

CONCLUSIONS

We conclude that milk provides the same compensatory digestive activity after short-term storage, even at relatively high temperature, as when fed fresh to the infant.

Digestive lipases of the newborn ferret: compensatory role of milk bile salt-dependent lipase

The amount of mRNA hybridizing to bile salt-dependent lipase and to colipase-dependent lipase probes as well as their translation into active proteins were quantified in the adult and newborn pancreas and lactating mammary gland from the ferret, a species whose milk, similar to that of the human, has bile salt-dependent lipase. The concentration of colipase-dependent lipase mRNA correlated with the amount of activity found in the adult and newborn pancreas, whereas neither mRNA nor activity of this enzyme was detected in the kit pancreas or in the lactating mammary gland. These data indicate that colipase-dependent lipase is actually expressed in adult pancreas and might represent the main lipolytic system in the adult. mRNA hybridizing to the bile salt-dependent lipase probe used in this study were detected in adult and in newborn ferret pancreas as well as in lactating mammary gland. However, the bile salt-dependent lipase activity expressed in the newborn pancreas was very low when compared with the activity expressed either in the mammary gland or in the adult pancreas. These data argue for a compensatory role of milk bile salt-dependent lipase in lipid digestion in the newborn. The hydrolysis of dietary fat might be initiated by preduodenal lipase, the activity of which is only two times lower in the gastric mucosa of the newborn than in the adult ferret. The high concentration of mRNA hybridizing to the bile salt-dependent lipase probe associated with a very poor bile salt-dependent lipase activity and protein suggests either that these mRNA are very unstable or that they are poorly translated into an active pancreatic bile salt-dependent lipase.

Lipid metabolism in pediatric nutrition

The abrupt transition from carbohydrate to fat as the main energy source that occurs at birth is not matched by commensurate endogenous fat-digesting capacity in the newborn. Newborn infants are, however, able to digest fat efficiently through the activities of gastric lipase and the exogenous digestive lipase of human milk, which compensate for the low activity of pancreatic lipase. Fat absorption is well-developed at birth and is commensurate with the high fat intake of the infant. Tissue uptake of dietary fat is also adequate, based on sufficient lipoprotein lipase (above 26 to 27 weeks' gestation) and rapid postnatal increase of lecithin:cholesterol acyl transferase, the enzymes that regulate tissue uptake of circulatory lipoprotein triglyceride and cholesterol.