Ontogeny of human gastric lipase and pepsin activities

Physiology of the Neonatal Gastrointestinal System Relevant to the Disposition of Orally Administered Medications

A thorough knowledge of the newborn (age, birth to 1 month postpartum) infant's gastrointestinal tract (GIT) is critical to the evaluation of the absorption, distribution, metabolism, and excretion (ADME) of orally administered drugs in this population. Developmental changes in the GIT during the newborn period are important for nutrient uptake as well as the disposition of orally administered medications. Some aspects of gastrointestinal function do not mature until driven by increased dietary complexity and nutritional demands later in the postnatal period. The functionalities present at birth, and subsequent maturation, can also impact the ADME parameters of orally administered compounds. This review will examine some specific contributors to the ADME processes in human neonates, as well as what is currently understood about the drivers for their maturation. Key species differences will be highlighted, with a focus on laboratory animals used in juvenile toxicity studies. Because of the gaps and inconsistencies in our knowledge, we will also highlight areas where additional study is warranted to better inform the appropriate use of medicines specifically intended for neonates.

Gastrointestinal Development: Implications for Management of Preterm and Term Infants

The gastrointestinal (GI) system provides digestive, absorptive, neuroendocrine, and immunologic functions to support overall health. If normal development is interrupted, a variety of complications and disease can arise. This article explores normal development of the GI tract and specific clinical challenges pertinent to preterm and term infants. Specific topics include abnormal motility, gastroesophageal reflux, current feeding recommendations for preterm infants, effects of parenteral nutrition, and the relationship between the GI tract and the immune system.

Scientific opinion on pesticides in foods for infants and young children

Following a request from the European Commission, the EFSA Panel on Plant Protection Products and their Residues (PPR Panel) prepared a scientific opinion to provide a comprehensive evaluation of pesticide residues in foods for infants and young children. In its approach to develop this scientific opinion, the EFSA PPR Panel took into account, among the others, (i) the relevant opinions of the Scientific Committee for Food setting a default maximum residue level (MRL) of 0.01 mg/kg for pesticide residues in foods for infants and young children; (ii) the recommendations provided by EFSA Scientific Committee in a guidance on risk assessment of substances present in food intended for infants below 16 weeks of age; (iii) the knowledge on organ/system development in infants and young children. For infants below 16 weeks of age, the EFSA PPR Panel concluded that pesticide residues at the default MRL of 0.01 mg/kg for food for infants and young children are not likely to result in an unacceptable exposure for active substances for which a health-based guidance value (HBGV) of 0.0026 mg/kg body weight (bw) per day or higher applies. Lower MRLs are recommended for active substances with HBGVs below this value. For infants above 16 weeks of age and young children, the established approach for setting HBGVs is considered appropriate. For infants below 16 weeks of age the approach may not be appropriate and the application of the EFSA guidance on risk assessment of substances present in food intended for infants below 16 weeks of age is recommended. The contribution of conventional food to the total exposure to pesticide residues is much higher than that from foods intended for infants and young children. Because of the increased intake of conventional food by young children, these have the highest exposure to pesticide residues, whereas infants 3-6 months of age generally have lower exposure. The impact of cumulative exposure to pesticide residues on infants and young children is not different from the general population and the EFSA cumulative risk assessment methodology is also applicable to these age groups. Residue definitions established under Regulation (EC) No 396/2005 are in general considered appropriate also for foods for infants and young children. However, based on a tier 1 analysis of the hydrolysis potential of pesticides simulating processing, the particular appropriateness of existing residue definitions for monitoring to cover processed food, both intended for infants and young children as well as conventional food, is questionable.

Guidance on the risk assessment of substances present in food intended for infants below 16 weeks of age

Following a request from the European Commission to EFSA, the EFSA Scientific Committee (SC) prepared a guidance for the risk assessment of substances present in food intended for infants below 16 weeks of age. In its approach to develop this guidance, the EFSA SC took into account, among others, (i) an exposure assessment based on infant formula as the only source of nutrition; (ii) knowledge of organ development in human infants, including the development of the gut, metabolic and excretory capacities, the brain and brain barriers, the immune system, the endocrine and reproductive systems; (iii) the overall toxicological profile of the substance identified through the standard toxicological tests, including critical effects; (iv) the relevance for the human infant of the neonatal experimental animal models used. The EFSA SC notes that during the period from birth up to 16 weeks, infants are expected to be exclusively fed on breast milk and/or infant formula. The EFSA SC views this period as the time where health-based guidance values for the general population do not apply without further considerations. High infant formula consumption per body weight is derived from 95th percentile consumption. The first weeks of life is the time of the highest relative consumption on a body weight basis. Therefore, when performing an exposure assessment, the EFSA SC proposes to use the high consumption value of 260 mL/kg bw per day. A decision tree approach is proposed that enables a risk assessment of substances present in food intended for infants below 16 weeks of age. The additional information needed when testing substances present in food for infants below 16 weeks of age and the approach to be taken for the risk assessment are on a case-by-case basis, depending on whether the substance is added intentionally to food and is systemically available.

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.

Isolation and functional studies of human fetal gastric epithelium in primary culture

Our understanding of gastric epithelial physiology in man is limited by the absence of normal or appropriate cancer cell lines that could serve as an in vitro model. Research mostly relied on primary culture of gastric epithelial cells of animal species, enriched with surface mucous cells, and devoid of glandular zymogenic chief cells. We successfully applied a new nonenzymatic procedure using Matrisperse Cell Recovery Solution to dissociate the entire epithelium from human fetal stomach. Cultures were generated by seeding multicellular aggregates prepared by mechanical fragmentation. We further demonstrate that this simple and convenient technique allows for the maintenance of heterogenous gastric epithelial primary cultures on plastic without a biological matrix as well as the persistence of viable chief cells able to synthesize and secrete gastric digestive enzymes, i.e., pepsinogen and gastric lipase. In wounding experiments, epithelial restitution occurred in serum-reduced conditions and was modulated by exogenous agents. This culture system is thus representative of the foveolus-gland axis and offers new perspectives to establish the influence of individual growth factors and extracellular matrix components as well as their combinatory effects on gastric epithelium homeostasis.

Functional development of human fetal gastrointestinal tract

The morphological development of the gastrointestinal tract (GI), in laboratory animals as well as in humans, has been well described since more than 100 years. However, even though its functional development and regulatory mechanisms are pretty well understood, our knowledge of the human GI functions originated primarily from studies on rat and mouse. Because of clear differences in genetic make up, development rates and sequences, as well as physiological differences, extrapolations of animal data to the human must be made with caution. A reliable organ culture technique in which the morphological as well as physiological parameters are well maintained has been set up. This technique allows studies of basic physiological functions such as gene expression, localization of specific cell markers, numerous digestive enzymatic activities, and lipid and lipoprotein processing. Furthermore, it also permits to determine and characterize the biological actions of potential regulators such as growth factors and hormones. Finally, the establishment of human intestinal epithelial cell lines allows the validation and the characterization of the molecular mechanisms involved in the specific regulatory pathways of the human GI development.

Establishment of human gastric epithelial (HGE) cell lines exhibiting barrier function, progenitor, and prezymogenic characteristics

The unavailability of human cell lines representative of the gastric glandular epithelium while able to form a functional barrier restricts the application of a cell culture approach to the field of gastric epithelial physiology. In the current study, we have characterized new non-transfected clones isolated from gastric carcinoma cell lines known to express functional markers of the human gastric mucosa (J Cell Biochem 2001;81:241). Twenty-one clones exhibiting epithelial-type junctions (renamed HGE cell lines) were isolated from NCI-N87 (ATCC CRL 5822), whereas only squamous cell lines could be generated from other native strains. Of these 21 clones, HGE-17 and HGE-20 formed dense coherent monolayers and displayed true epithelial phenotype. E-cadherin and ZO-1 proteins were consistently localized at the periphery of all cells which also generated transepithelial electrical resistance. Moreover, growth factors known to be trophic for the gastric mucosa were able to stimulate mitogenesis at subconfluence. HGE-17 exhibited a poorly differentiated precursor-like status and responded strongly to EGF/TGFalpha treatment in restitution assays. HGE-20 cells, on the other hand, exhibited a higher degree of differentiation at the ultrastructural level as well as higher gastric lipase and pepsinogen levels. These latter zymogens were compartmentalized into granules which also contained mucin-6 (MUC6, prezymogenic-like status). Exogenous hormones, i.e., 1 mug/ml hydrocortisone and 5 microM retinoic acid, significantly increased enzyme levels in HGE-20. In conclusion, HGE-17 and HGE-20 represent the first human gastric cell lines with true epithelial characteristics, opening a venue to important applications for the study of re-epithelization, permeability, and regulation of digestive functions in the context of gastric physiology and pathology.

Potential host-defense role of a human milk vitamin B-12-binding protein, haptocorrin, in the gastrointestinal tract of breastfed infants, as assessed with porcine haptocorrin in vitro

BACKGROUND

Limited information exists on the biological role of a vitamin B-12-binding protein, haptocorrin, in human milk. The expression of haptocorrin by human mammary epithelial cells and its presence in human milk suggest a potential physiologic function in breastfed infants.

OBJECTIVE

We investigated the extent to which haptocorrin could withstand proteolytic degradation and exert antimicrobial activity under in vitro conditions designed to simulate the gastrointestinal tract of breastfed infants.

DESIGN

An in vitro model that simulates infant gastric and intestinal digestion was developed. The structural stability of porcine haptocorrin after exposure to digestive enzymes (pepsin and pancreatin) was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blot analysis, column chromatography, and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The antimicrobial activity of haptocorrin was determined by incubating haptocorrin with enteropathogenic Escherichia coli O127 strain 2348/69 and monitoring bacterial growth.

RESULTS

The structural analysis of haptocorrin exposed to enzymes did not show a decrease in molecular weight, which indicated that haptocorrin can survive proteolytic degradation. Both haptocorrin exposed to digestive enzymes and undigested haptocorrin inhibited the growth of enteropathogenic E. coli and did so to a similar extent. Thus, haptocorrin in vitro not only retains its structure after exposure to proteases but also exhibits antimicrobial activity.

CONCLUSION

These results suggest that haptocorrin may exert a host-defense function against pathogens in the gastrointestinal tracts of breastfed infants.

Gastric proteolysis in preterm infants fed mother's milk or formula

Gastric proteolysis is assumed to be low in the newborn (Britton & Koldovsky 1989). Postprandial pepsin output is significantly lower in preterm infants than adults, 589 vs. 3352U/kg, respectively (Armand et al. 1995, 1996). We now report on gastric proteolysis in preterm infants (gestation age, 29 weeks; postnatal age, 5-6 weeks) gavage-fed mother's milk or preemie formula. The data show that a) the nonprotein component is higher in human milk than formula, b) net proteolysis amounts to 15% of protein, c) gastric proteolysis is lower than lipolysis and, contrary to the latter, is not enhanced by milk feeding (Armand et al. 1996). We suggest that stomach pH, enzyme output, and food structure are the reasons for differences in gastric digestion of protein and fat in infants.

Nutrient requirements for preterm infant formulas

Achieving appropriate growth and nutrient accretion of preterm and low birth weight (LBW) infants is often difficult during hospitalization because of metabolic and gastrointestinal immaturity and other complicating medical conditions. Advances in the care of preterm-LBW infants, including improved nutrition, have reduced mortality rates for these infants from 9.6 to 6.2% from 1983 to 1997. The Food and Drug Administration (FDA) has responsibility for ensuring the safety and nutritional quality of infant formulas based on current scientific knowledge. Consequently, under FDA contract, an ad hoc Expert Panel was convened by the Life Sciences Research Office of the American Society for Nutritional Sciences to make recommendations for the nutrient content of formulas for preterm-LBW infants based on current scientific knowledge and expert opinion. Recommendations were developed from different criteria than that used for recommendations for term infant formula. To ensure nutrient adequacy, the Panel considered intrauterine accretion rate, organ development, factorial estimates of requirements, nutrient interactions and supplemental feeding studies. Consideration was also given to long-term developmental outcome. Some recommendations were based on current use in domestic preterm formula. Included were recommendations for nutrients not required in formula for term infants such as lactose and arginine. Recommendations, examples, and sample calculations were based on a 1000 g preterm infant consuming 120 kcal/kg and 150 mL/d of an 810 kcal/L formula. A summary of recommendations for energy and 45 nutrient components of enteral formulas for preterm-LBW infants are presented. Recommendations for five nutrient:nutrient ratios are also presented. In addition, critical areas for future research on the nutritional requirements specific for preterm-LBW infants are identified.

Laminins and TGF-beta maintain cell polarity and functionality of human gastric glandular epithelium

The human gastric glandular epithelium produces a gastric lipase enzyme (HGL) that plays an important role in digestion of dietary triglycerides. To assess the involvement of extracellular matrix components and transforming growth factor-beta1 (TGF-beta1) in the regulation of this enzymic function, normal gastric epithelial cells were cultured on collagen type I, Matrigel, and laminins (LN)-1 and -2 with or without TGF-beta1. Epithelial morphology and HGL expression were evaluated using microscopy techniques, enzymic assays, Western blot, Northern hybridization, and RT-PCR. A correlation was observed between the cell polarity status and the level of HGL expression. TGF-beta1 alone or individual matrix components stimulated cell spreading and caused a downfall of HGL activity and mRNA. By contrast, Matrigel preserved the morphological features of differentiated epithelial cells and maintained HGL expression. The combination of LNs with TGF-beta1 (two constituents of Matrigel) exerted similar beneficial effects on epithelial cell polarity and evoked a 10-fold increase of HGL levels that was blunted by a neutralizing antibody against the alpha(2)-integrin subunit and by mitogen-activated protein kinase (MAPK) inhibitors PD-98059 (p42/p44) or SB-203580 (p38). This investigation demonstrates for the first time that a powerful synergism between a growth factor and basement membrane LNs positively influences cell polarity and functionality of the human gastric glandular epithelium through an activation of the alpha(2)beta(1)-integrin and effectors of two MAPK pathways.

Morphologic and functional development of whole human fetal stomachs grafted into nude mice

To study in vivo the cellular differentiation and secretion of human developing fetal stomach, ethically and technically impossible to perform in utero, 256 fetal stomachs were xenografted. Human stomachs from 6- to 10-week-old fetuses were grafted for 1-273 days into nude mice. Biopsies for immunohistochemistry, hybridization and electron microscopy were taken and a catheter introduced into the human stomach. Macroscopic growth was fast and cells in S phase were numerous during the first 9 weeks, then the stomach size was stable and the gastric mucosa, of adult type, remained normal. In situ hybridization detected only a minute mouse mesenchymal chimerism in the graft. Chromogranin A, intrinsic factor and H+/K+ adenosine triphosphatase were immunohistolocally detected in epithelial cells 20 days after grafting, gastrin was detected after 30 days and pepsinogen after 60 days. The pH in gastric juice, which was at 8.0 +/- 0.1 from days 10-25, dropped from 4.39 +/- 1.80 at 30 days to 1.58 +/- 0.29 at 90 days. Intrinsic factor was stable and pepsin ranged from 6.8 +/- 7.8 to 134 +/- 51 units at 90 days. The differentiation of the epithelial cells in xenografts was very accelerated in comparison to that in utero.

Establishment of culture systems of human gastric epithelium for the study of pepsinogen and gastric lipase synthesis and secretion

A main purpose of gastric secretion pertains to the digestion of dietary proteins and involves the release of pepsinogens by the fundic and antral mucosa. Over the last decade, data on human gastric physiology has expanded to equally include a significant role in fat digestion. Characteristics of human gastric lipase (HGL) such as optimum acid pH, resistance to proteolysis and non requirement of bile salts or cofactors, are advantageous in gastric lipolysis. Furthermore, the importance of HGL increases in the context of perinatal physiology and pathological situations where secretion of HGL could compensate, to some extent the depressed pancreatic activities. It is therefore important to understand the regulatory mechanisms involved in the synthesis and secretion of human gastric digestive enzymes. The establishment of an organ culture technique as well as a novel primary culture system of human gastric epithelium permitted us to demonstrate that Pg5 and HGL are colocalized in human chief cells and both digestive enzymes are efficiently synthesized and secreted in explants and primary cultures. Pepsin activity rises at the cellular level while its secretion remains constant. In contrast, cellular lipase activity drastically diminishes while being preferentially secreted. This nonparallelism supports the concept that Pg5 and HGL are differently regulated in culture. Furthermore, EGF downregulates HGL expression at the mRNA level via the p42/44(MAPK) pathway without affecting Pg5. Future studies should be designed to fully understand the cellular and molecular mechanisms involved in regulating HGL activity in normal and pathological conditions.

A new primary culture system representative of the human gastric epithelium

The gastric pit-gland unit is a highly dynamic and compartimentalized structure which assumes important key functions such as acid secretion, digestion of dietary proteins and triglycerides, protection, and epithelial restitution following injury. However, in vitro models representative of the intact gastric epithelium are still lacking. The current study was undertaken to investigate the possibility of generating such primary cultures from human fetal stomach. The use of Matrisperse, a nonenzymatic solution, allowed complete dissociation of the epithelial layer and the maintenance for at least 7 days of all gastric epithelial cell types in primary culture on plastic. Indirect immunofluorescence and Western blot analyses confirmed the purity of epithelial cultures, composed of 60% mucus-secreting cells, 25% zymogenic chief cells, 5% parietal cells, and a small proportion of mitotic precursors. Their functionality was demonstrated by the presence of zonulae occludens and adherens at cell to cell contacts, [(3)H]thymidine incorporation, Periodic acid Schiff staining, and expression of growth factor receptors (EGF/TGFalpha, IGF1, HGF, KGF), gastric H(+)/K(+)-ATPase, pepsinogen (Pg5), and human gastric lipase (HGL). Chief cells were able to produce and secrete both Pg5 and HGL and to respond to EGF treatment. In conclusion, we developed a new primary culture system of human gastric epithelium characterized for the first time by the absence of added matrix and the maintenance of functional chief cells. It represents an experimental breakthrough that will serve applications in investigating the actions of hormones, mesenchymal growth factors, and basement membrane proteins on human gastric functions in vitro.

Architecture of blood vessels in human fetal gastric corpus: a corrosion casting study

Vascular architecture of the gastric corpus was investigated in 16-24 wk human fetuses using a corrosion casting technique and the scanning electron microscopy. The general distribution of blood vessels seen in adults has already been established in the fetus, with three major vascular plexuses located in the serosa, submucosa and mucosa. The serosal plexus, supplied and drained by large extramural vessels, contained anastomosing, arcade-like arrays of arteries and veins with their branches piercing the muscularis and communicating with the compact submucosal plexus. Vertical arterioles and capillaries were sent by submucosal arteries to supply a very dense capillary plexus which surrounded the gastric pits and consisted of wide, sinusoidal vessels showing morphological manifestations of angiogenesis by intussusceptive growth. The plexus was drained by vertical venules emptying into submucosal veins. In contrast to the richly vascularized upper half of the mucosa, the lower half showed a relative paucity of blood vessels, probably due to the thinness of the fetal mucosa allowing an effective diffusion of oxygen and nutrients from the upper half. Neither arteriovenous anastomoses, nor end-arteries were found in the fetal stomach. Results of this study support one of the two existing models of mucosal vascularization in the human stomach: i.e. the model postulating the presence of short and long arterioles and two distinct, albeit interconnected capillary networks in the upper and lower zones of the mucosa respectively. In human fetuses, the latter network is absent; it probably develops by remodelling of the preexisting vertical capillaries in the last phase of pregnancy, prior to the onset of gastric gland function.

Epidermal growth factor and transforming growth factor alpha down-regulate human gastric lipase gene expression

BACKGROUND & AIMS

It was recently reported that human gastric lipase (HGL) activity is modulated by epidermal growth factor (EGF). The aims of this study were to establish the cellular localization of HGL, to assess the correlation between HGL messenger RNA (mRNA) and protein levels, and to establish the molecular mechanism of action of EGF and its homologue transforming growth factor alpha (TGF-alpha) on HGL expression.

METHODS

Cellular localization of HGL was determined by immunohistochemistry using a polyclonal antibody. Enzymic determinations, Western blotting, and Northern hybridization were used to analyze expression of HGL mRNA, protein, lipase activity, and the p42/p44(mapk) activation status.

RESULTS

HGL was localized in the secretory granules of gastric chief cells as early as 13 weeks. A close parallelism was found between the variations of mRNA, protein, and enzymic activity. EGF and/or TGF-alpha down-regulated HGL mRNA levels and decreased enzymic activity. The role of the mitogen-activated protein kinase cascade in the regulation of HGL expression was highlighted by the use of MAP kinase kinase-1/2 inhibitor PD98059, which blunted both the activation of p42/p44(mapk) and the down-regulation of HGL mRNA induced by EGF and/or TGF-alpha.

CONCLUSIONS

The expression of HGL is regulated at the mRNA level, and the down-regulatory action of EGF and/or TGF-alpha on HGL involves the stimulation of p42/p44(mapk) cascade.

Development of the human gastrointestinal tract: twenty years of progress

A combination of approaches has begun to elucidate the mechanisms of gastrointestinal development. This review describes progress over the last 20 years in understanding human gastrointestinal development, including data from both human and experimental animal studies that address molecular mechanisms. Rapid progress is being made in the identification of genes regulating gastrointestinal development. Genes directing initial formation of the endoderm as well as organ-specific patterning are beginning to be identified. Signaling pathways regulating the overall right-left asymmetry of the gastrointestinal tract and epithelial-mesenchymal interactions are being clarified. In searching for extrinsic developmental regulators, numerous candidate trophic factors have been proposed, but compelling evidence remains elusive. A critical gene that initiates pancreas development has been identified, as well as a number of genes regulating liver, stomach, and intestinal development. Mutations in genes affecting neural crest cell migration have been shown to give rise to Hirschsprung's disease. Considerable progress has been achieved in understanding specific phenomena, such as the transcription factors regulating expression of sucrase-isomaltase and fatty acid-binding protein. The challenge for the future is to integrate these data into a more complete understanding of the physiology of gastrointestinal development.

Uptake and metabolism of structured triglyceride by Caco-2 cells: reversal of essential fatty acid deficiency

Structured lipids have been proposed as efficient vehicles for the supplementation of essential fatty acids (EFA) to patients with malabsorption. We investigated how a novel structured triglyceride (STG), containing purely octanoic acid in the sn-1/sn-3 and [14C]linoleic acid in the sn-2 positions, was incorporated into different lipid classes in Caco-2 cells. We also evaluated the contribution of gastric lipase in the uptake and metabolism of [14C]linoleic acid from the STG. We furthermore determined the potential of the STG to correct EFA deficiency induced in Caco-2 cells. The absorption of STG by Caco-2 cells was significantly greater compared with that of triolein. The addition of human gastric lipase significantly enhanced cellular uptake of the labeled substrate, reflecting the stereoselectivity of gastric lipase to hydrolyze medium chain FA. Analysis of the intracellular lipids synthesized revealed a predominance of phospholipids-monoglycerides. Most of the radioactivity in the lipoproteins isolated from Caco-2 cells was recovered in TG-rich lipoproteins (45%) and to a lesser extent in the high-density lipoprotein (36%) and low-density lipoprotein (17%) fractions. The administration of STG to Caco-2 cells rendered EFA deficient produced a marked increase of the cellular level of linoleic and arachidonic acids. This resulted in a lower ratio of 20:3(n-9) to 20:4(n-6), reflecting the correction of EFA deficiency in Caco-2 cells. Our data demonstrate that STG, in the presence of gastric lipase, have beneficial effects on lipid incorporation, lipoprotein production, and EFA status, utilizing Caco-2 cells as a model of EFA deficiency.

Endogenous lipase activity in Caco-2 cells

Dietary triglycerides, the major precursors of long chain fatty acids (FA), require hydrolysis by pancreatic enzymes prior to their absorption by the small intestine. Although Caco-2 cells are frequently employed for the study of enterocyte lipid metabolism, the presence of an endogenous lipase activity has never been previously reported. The major goal of this investigation was to determine the presence of endogenous Caco-2 cell lipase activity, to examine its capacity to hydrolyze triglycerides, and to define its intracellular location. Caco-2 cells were found to have an endogenous lipase activity, capable of hydrolyzing [1-14C]triolein from the apical cell compartment. A time and concentration dependence of lipase activity was observed, with hydrolysis of triolein into free fatty acids and monoglyceride. The majority of the lipase activity was found in the cytosolic cell fraction and, to a lesser extent, in the apical brush border membrane and other organelles. Protamine sulfate markedly reduced the Caco-2 cell lipase activity, yet it remained relatively insensitive to high concentrations of NaCl, taurocholate, calcium, heparin and chloroquine. The addition of exogenous human gastric lipase to the medium of the apical compartment resulted in a significant increased rate of hydrolysis of triolein, followed by enhanced Caco-2 cell fatty acid uptake and basolateral lipid secretion. The major esterified intracellular lipids were triglycerides and phospholipids. We conclude that Caco-2 cells possess an endogenous lipase capable of hydrolyzing cytosolic triglycerides. Furthermore, activity present on the apical membrane and secreted into the apical medium, though quantitatively less important than the cytosolic lipase, may permit an additional route for energy uptake. The addition of gastric lipase to the Caco-2 cell cultures greatly enhanced FA uptake above that seen with the endogenous lipase alone.

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.

Differential expression of extracellular matrix components during the morphogenesis of human gastric mucosa

BACKGROUND

Components of extracellular matrix play a crucial role in morphogenesis and epithelial cell differentiation. In this study, we examined the spatiotemporal expression and distribution of several major extracellular macromolecules of developing and adult human gastric mucosa, with particular emphasis on the pit-gland axis.

METHODS

Indirect immunofluorescence was performed on cryosections of developing and adult gastric tissues by using specific antibodies.

RESULTS

From 8 weeks of gestation onward, including adults, heparan sulfate proteoglycan, type IV collagen, and laminin alpha 1, beta 1, and gamma 1 chains were systematically and uniformly located at the basement membrane of the stratified epithelium (8-11 weeks) and of surface and pit-gland epithelia. Between 8 and 20 weeks of gestation, fibronectin and tenascin were colocalized throughout the entire mesenchyme. In adult mucosa, fibronectin was distributed at all levels of surface and glandular epithelium, whereas tenascin expression was restricted to surface and pit epithelial cells. The expression of the alpha 2 laminin chain was first detected at 12 weeks at the base of forming gastric glands. In the adult, the alpha 2 as opposed to the alpha 1 chain of laminin was confined to the basement membrane of the glandular and lower part of gastric pit epithelia.

CONCLUSIONS

This analysis of the composition of the extracellular matrix in human gastric mucosa suggests an important role for some of its components in morphogenesis and maintenance of gastric glands.