Brush Border Hydrolases Research Articles

A CRISPR screen in intestinal epithelial cells identifies novel factors for polarity and apical transport.

Epithelial polarization and polarized cargo transport are highly coordinated and interdependent processes. In our search for novel regulators of epithelial polarization and protein secretion, we used a genome-wide CRISPR/Cas9 screen and combined it with an assay based on fluorescence-activated cell sorting (FACS) to measure the secretion of the apical brush-border hydrolase dipeptidyl peptidase 4 (DPP4). In this way, we performed the first CRISPR screen to date in human polarized epithelial cells. Using high-resolution microscopy, we detected polarization defects and mislocalization of DPP4 to late endosomes/lysosomes after knockout of TM9SF4, anoctamin 8, and ARHGAP33, confirming the identification of novel factors for epithelial polarization and apical cargo secretion. Thus, we provide a powerful tool suitable for studying polarization and cargo secretion in epithelial cells. In addition, we provide a dataset that serves as a resource for the study of novel mechanisms for epithelial polarization and polarized transport and facilitates the investigation of novel congenital diseases associated with these processes.

The Proteome of Filter-Grown Caco-2 Cells With a Focus on Proteins Involved in Drug Disposition

Caco-2 cells are widely used in studies of intestinal cell physiology and drug transport. Here, the global proteome of filter-grown Caco-2 cells was quantified using the total protein approach and compared with the human colon and jejunum proteomes. In total, 8096 proteins were identified. In-depth analysis of proteins defining enterocyte differentiation—including brush-border hydrolases, integrins, and adherens and tight junctions—gave near-complete coverage of the expected proteins. Three hundred twenty-seven absorption, distribution, metabolism and excretion proteins were identified, including 112 solute carriers and 20 ATP-binding cassette transporters. OATP2B1 levels were 16-fold higher in Caco-2 cells than in jejunum. To investigate the impact of this difference on in vitro-in vivo extrapolations, we studied the uptake kinetics of the OATP2B1 substrate pitavastatin in Caco-2 monolayers, and found that the contribution of OATP2B1 was 60%-70% at clinically relevant intestinal concentrations. Pitavastatin kinetics was combined with transporter concentrations to model the contribution of active transport and membrane permeation in the jejunum. The lower OATP2B1 expression in jejunum led to a considerably lower transporter contribution (<5%), suggesting that transmembrane diffusion dominates pitavastatin absorption in vivo. In conclusion, we present the first in-depth quantification of the filter-grown Caco-2 proteome. We also demonstrate the crucial importance of considering transporter expression levels for correct interpretation of drug transport routes across the human intestine.

Structural changes induced by heating affect ovalbumin-antigen processing and reduce allergic response in mouse model of food allergy

Background Food allergy is a serious health concern affecting about 8% of young children and about 3% of adults. The egg protein ovalbumin belongs among six frequent food allergens. Our goal was to develop the mouse model of ovalbumin food allergy and investigate how thermal processing affects its ability to induce allergic responses. Methods Effect of thermal processing (70°C and 95°C) on an ovalbumin secondary structure was characterized by circular dichroism and by kinetics of pepsin digestion with subsequent HPLC analysis. BALB/c mice were sensitized intraperitoneally and challenged intragastrically with native form or thermal processed ovalbumin (70°C). Clinical symptoms (allergic diarrhea, weight and temperature) were observed during the mice challenging. Levels of allergen-specific serum antibodies were determined by ELISA (IgA, IgG1 and IgG2a) by beta-hexosaminidase release test (IgE). Cytokine production (IL-4, IL-5, IL-6, IL-10, IL-13, IL-17, IFN-gamma) and mast cell protease-1 activity were assessed by ELISA. The activities of brush-border hydrolases were determined in the jejunum of treated mice. Results Heating of ovalbumin caused slight irreversible changes in secondary structure and significantly decreased clinical symptoms (allergic diarrhea). The thermal processing also decreased immune allergic response on the level of IgE, IL-4, IL-5, IL-13. Furthermore, thermal-processed ovalbumin induced lower activities of serum mast cell protease-1 and enterocyte brush border membrane alkaline phosphatase as compared to native ovalbumin. On the other hand, thermal-processed ovalbumin stimulated higher IgG2a antibodies in sera and IFN-gamma secretion by splenocytes. Conclusion In our mice model of food allergy, we show that even a slight change in the secondary structure of ovalbumin after thermal processing reduces its allergenicity and induces shift towards Th1 immune responses. At present, we utilize this model for studying of food allergy in germfree mice.

The dual role of annexin II in targeting of brush border proteins and in intestinal cell polarity

Functional intestinal epithelium relies on complete polarization of enterocytes marked by the formation of microvilli and the accurate trafficking of glycoproteins to relevant membrane domains. Numerous transport pathways warrant the unique structural identity and protein/lipid composition of the brush border membrane. Annexin II (Ca 2+-dependent lipid-binding protein) is an important component of one of the apical protein transport machineries, which involves detergent-resistant membranes and the actin cytoskeleton. Here, we investigate in intestinal Caco-2 cells the contribution of annexin II to the sorting and transport of brush border hydrolases and role in intestinal cell polarity. Downregulation of annexin II in Caco-2-A4 cell line results in a severe reduction of the levels of the brush border membrane resident enzyme sucrase isomaltase (SI) as well as structural components such as ezrin. This reduction is accompanied by a redistribution of these proteins to intracellular compartments and a striking morphological transition of Caco-2 cells to rudimentary epithelial cells that are characterized by an almost flat apical membrane with sparse and short microvilli. Concomitant with this alteration is the redistribution of the intermediate filament protein keratin 19 to the intracellular membranes in Caco-2-A4 cells. Interestingly, keratin 19 interacts with annexin II in wild type Caco-2 cells and this interaction occurs exclusively in lipid rafts. Our findings suggest a role for annexin II and K19 in differentiation and polarization of intestinal cells.

Lipid raft organization and function in the small intestinal brush border

The enterocyte brush border of the small intestine is a highly specialized membrane designed to function both as a high capacity digestive/absorptive surface of dietary nutrients and a permeability barrier towards lumenal pathogens. It is characterized by an unusually high content of glycolipids (approximately 30% of the total microvillar membrane lipid), enabling the formation of liquid ordered microdomains, better known as lipid rafts. The glycolipid rafts are stabilized by galectin-4, a 36 kDa divalent lectin that cross-links galactosyl (and other carbohydrate) residues present on membrane lipids and several brush border proteins, including some of the major hydrolases. These supramolecular complexes are further stabilized by intelectin, a 35 kDa trimeric lectin that also functions as an intestinal lactoferrin receptor. As a result, brush border hydrolases, otherwise sensitive to pancreatic proteinases, are protected from untimely release into the gut lumen. Finally, anti-glycosyl antibodies, synthesized by plasma cells locally in the gut, are deposited on the brush border glycolipid rafts, protecting the epithelium from lumenal pathogens that exploit lipid rafts as portals for entry to the organism.

Loss of galectin-3 impairs membrane polarisation of mouse enterocytes in vivo

Epithelial cells are characterised by distinct apical and basolateral membrane domains that are separated by tight junctions. Establishment and maintenance of this polarity depend on specific gene expression and protein targeting to their correct location. Our former studies, performed with renal epithelial MDCK cells, revealed a new function for galectin-3, a member of a conserved family of lectins. There, galectin-3 is required for intracellular sorting and correct targeting of non-raft-associated glycoproteins to the apical plasma membrane. In the present study, we found transport defects of the intestinal brush border hydrolases lactase-phlorizin hydrolase (LPH) and dipeptidylpeptidase IV (DPPIV) in galectin-3-null mutant mice. We could show that, in enterocytes of wild-type mice, both glycoproteins directly interact with galectin-3 and transit through non-raft-dependent apical transport platforms. Therefore, this genetic analysis provides definitive evidence for the involvement of galectin-3 in protein intracellular trafficking in vivo. Further investigations revealed that gal3-null enterocytes also exhibit striking cytoarchitecture defects, with the presence of numerous and regular protrusions located along basolateral membranes. Moreover, beta-actin and villin, two characteristic markers of brush borders, become abnormally distributed along these atypical basolateral membranes in gal3(-/-) mice. Taken together, our results demonstrate that, in addition to a pivotal role in apical trafficking, galectin-3 also participates in epithelial morphogenesis in mouse enterocytes.

Mosaic Pattern of Sucrase Isomaltase Deficiency in Two Brothers

The pathophysiology of mucosal changes observed in infants with chronic protracted diarrhea is poorly understood. We report on two brothers suffering from a special form of sucrase isomaltase (SI) deficiency. The children presented with weight loss and dyspepsia after sucrose exposition. We performed an H respiration test, which showed a pathologic result in the younger brother. Analysis of the brush border enzyme activities showed low expression of lactase and SI. Immunoelectron microscopy of duodenal biopsies showed an isolated SI deficiency in a mosaic pattern [e.g., 42% (14%) crypt enterocytes and 64% (59%) villus enterocytes with decreased amounts of SI on microvilli], whereas lactase and aminopeptidase n (ApN) were present at the apical membrane of all cells in a normal range. The SI mosaic pattern of these patients shows that the enterocytes contain low amounts of SI on the apical membrane but express normal quantities of other disaccharidases. These findings suggest the existence of different clonal expressions or specific (posttranslational) mechanisms of postGolgi transportation for individual brush border enzymes. It remains unresolved whether the mosaic distribution is part of a normal maturation process or caused by a lack of an overall control mechanism in the expression of brush border hydrolases.

Electroencephalography: Basic Principles, Clinical Applications, and Related Fields, Fifth Edition

Highly differentiated human proximal tubule (HPT) cells in primary culture were established from heterogeneous suspension of tubules prepared from the human renal cortex by an original two-step procedure. First, gluconeogenic-competent HPT cells were selected by using a hormonally defined serum-free medium without glucose or insulin; then, the selected HPT cells were grown in a medium containing a low concentration of glucose (1 mM) and insulin (0.5 micrograms/mL) but no antibiotics. HPT cells grown on plastic support formed confluent, cobblestone-like monolayers with numerous mitochondria and pinocytosis vacuoles, solitary cilia, junctional complexes, and a well-developed brush border consisting of densely packed microvilli. Compared with cell monolayers on plastic support, HPT cells grown on porous filter membranes showed better morphologic differentiation. HPT cell monolayers expressed the following differentiated functions of the proximal tubule in situ: a low-affinity, high-capacity Na(+)-dependent glucose transport system inhibited by phlorizin, a high-affinity Na(+)-dependent phosphate transport system, a basolateral organic cation uptake inhibited by mepiperphenidol, parathyroid hormone-sensitive cAMP synthesis, brush-border hydrolase activities, gluconeogenesis-associated enzymes, glutathione-S-transferases and N-acetyl-beta-D-glucosaminidase. The medium containing low glucose and insulin concentrations markedly limited the increase in glycolysis but did not prevent the falls in gluconeogenesis and brush-border hydrolase activity at any time of the culture period. Similar decreases of brush border enzyme activities were obtained for HPT cells grown either on plastic or on porous filter membrane. A thorough characterization study demonstrated that this simple and preparative experimental approach makes it possible to establish highly differentiated HPT cells in primary culture suitable for investigating human renal proximal tubular cell function.

Functional interaction of Escherichia coli heat‐labile enterotoxin with blood group A‐active glycoconjugates from differentiated HT29 cells

Human colon adenocarcinoma cells (HT29-ATCC) and the clone HT29-5F7 were cultured under conditions that differentiate cells to a polarized intestinal phenotype. Differentiated cells showed the presence of junctional complexes and intercellular lumina bordered by microvilli. Intestinal brush border hydrolase activities (sucrase, aminopeptidase N, lactase and maltase) were detected mainly in differentiated HT29-ATCC cells compared with the differentiated clone, HT29-5F7. The presence of non-GM1 receptors of Escherichia coli heat-labile enterotoxin (LT-I) on both types of differentiated HT29 cells was indicated by the inability of cholera toxin B subunit to block LT-I binding to the cells. Binding of LT-I to cells, when GM1 was blocked by the cholera toxin B subunit, was characterized by an increased number of LT-I receptors with respect to undifferentiated control cells. Moreover, both types of differentiated cells accumulated higher amounts of cyclic AMP in response to LT-I than undifferentiated cells. Helix pomatia lectin inhibited the binding of LT-I to cells and the subsequent production of cyclic AMP. LT-I recognized blood group A-active glycosphingolipids as functional receptors in both HT29 cell lines and the active pro-sucrase form of the glycoprotein carrying A-blood group activity present in HT29-ATCC cells. These results strongly suggest that LT-I can elicit an enhanced functional response using blood group A-active glycoconjugates as additional receptors on polarized intestinal epithelial cells.

Carbenoxolone accelerates maturation of rat intestine.

The rat undergoes profound maturational changes in the intestinal structure and function during the third week of its life. To investigate the role of peripheral glucocorticoid metabolism in this process, we studied the postnatal maturation of intestinal structure and function. The peripheral metabolism of glucocorticoids depends on enzyme 11beta-hydroxysteroid dehydrogenase (11betaHSD), which is responsible for the interconversion of corticosterone to 11-dehydrocorticosterone and thus for the modulation of glucocorticoid access to corticosteroid receptors. The pups were treated with carbenoxolone (CBX), an inhibitor of 11betaHSD, for 10 d during the suckling (days 8-18) or weaning period (days 14-24 or days 20-30), and we determined the parameters of intestinal growth and activities of sucrase, alkaline phosphatase, and Na,K-ATPase. The CBX treatment increased plasma concentrations of corticosterone as a result of a significant reduction of peripheral degradation of corticosterone catalyzed by 11betaHSD. This also stimulated intestinal growth without changing somatic growth. The mucosal cell mass was significantly higher in CBX-treated suckling rats, whereas the effect of this treatment was less obvious in weanling animals. CBX increased the crypt depth and villus height in 18- and 24-d-old pups but not in 30-d-old animals. The small intestinal activities of sucrase, alkaline phosphatase, and Na,K-ATPase were not influenced by CBX. In contrast, colonic Na,K-ATPase was stimulated by CBX. We conclude that the administration of CBX results in acceleration of intestinal growth and structural maturation without any influence on the developmental pattern of brush-border hydrolases. The results indicate an important role of peripheral glucocorticoid metabolism in the regulation of intestinal growth during early postnatal life.

Region-specific adaptation of apical Na/H exchangers after extensive proximal small bowel resection

After massive small bowel resection (MSBR), the remnant small intestine adapts to restore Na absorptive function. The possibility that this occurs through increases in cellular Na absorptive capacity was examined by assessing the regional effects of 50% proximal MSBR on the function and expression of the apical membrane Na/H exchangers (NHEs) NHE2 and NHE3. Morphometric analysis confirmed adaptive changes consistent with villus hypertrophy, particularly distal to the anastomosis. Villus epithelium prepared by light mucosal scrapings from 2-wk-postresected and -posttransected control rats exhibited comparable brush-border hydrolase activities, total cell protein per DNA, and villin expression but increased basolateral Na-K-ATPase activity. Parallel increases of two- to threefold in protein and mRNA abundance of NHE2 and NHE3 were observed only in ileal regions distal to the anastomosis of resected rats. Basolateral NHE1 expression was unchanged. After 80% resection, increases in NHE2 and NHE3 became evident in proximal colon. We conclude that increased enterocyte expression and function of apical membrane NHEs in regions distal to the anastomosis play a role in the adaptive process after MSBR. The increased luminal Na load to distal bowel regions after proximal resection may stimulate increases in apical membrane NHE gene transcription and protein expression.

Developmental regulation of intestinal epithelial hydrolase activity in human fetal jejunal xenografts maintained in severe-combined immunodeficient mice.

Intestinal epithelial brush border hydrolases are important and sensitive enzyme markers of gastrointestinal development and function. Little is know about the mechanisms that regulate the induction of these enzymes during human fetal development, as these events occur primarily in utero. The present work used ectopically grafted human fetal jejunal xenografts (median age,13.3 wk of gestation), maintained in severe-combined immunodeficient mice, to study the differential expression of five different hydrolases after 10 wk of xenotransplantation. The spatio-temporal distribution of brush border alkaline phosphatase, aminopeptidase-N, alpha-glucosidase, lactase-phlorizin hydrolase, and dipeptidyl peptidase IV enzyme activities were measured quantitatively using scanning microdensitometry along the crypt-villus axes of fetal, xenograft, and pediatric (median age, 34 mo) biopsies. Ectopic grafting of fetal jejunum closely recapitulated the development of these enzymes in utero, with alkaline phosphatase, aminopeptidase-N, alpha-glucosidase, and dipeptidyl peptidase IV enzyme activities closely matching the spatio-temporal distribution and levels recorded in pediatric duodenal biopsies. Lactase-phlorizin hydrolase was the only enzyme not to reach values recorded in pediatric brush border membranes, although activities were significantly (5.6-fold) higher than in pretransplanted fetal bowel. Human jejunal xenografts therefore demonstrate an appropriate developmental induction of brush border hydrolase activity and may represent a useful model to study trans-acting factors that promote human epithelial differentiation and function in vivo. Characterization of such agents may be of potential therapeutic use in the treatment of diseases associated with gastrointestinal immaturity, notably necrotizing enterocolitis.

SCFA increase intestinal Na absorption by induction of NHE3 in rat colon and human intestinal C2/bbe cells.

Short-chain fatty acids (SCFA), produced by colonic bacterial flora fermentation of dietary carbohydrates, promote colonic Na absorption through mechanisms not well understood. We hypothesized that SCFA promote increased expression of apical membrane Na/H exchange (NHE), serving as luminal physiological cues for regulating colonic Na absorptive capacity. Studies were performed in human colonic C2/bbe (C2) monolayers and in vivo. In C2 cells exposed to butyrate, acetate, proprionate, or the poorly metabolized SCFA isobutyrate, apical membrane NHE3 activity and protein expression increased in a time- and concentration-dependent manner, whereas no changes were observed for NHE2. In contrast, no significant changes in brush-border hydrolase or villin expression were noted. Analogous to the in vitro findings, rats fed the soluble fiber pectin exhibited a time-dependent increase in colonic NHE3, but not NHE2, protein, mRNA, and brush-border activity. These changes were region-specific, as no changes were observed in the ileum. We conclude that luminal SCFA are important physiological cues for regulating colonic Na absorptive function, allowing the colon to adapt to chronic changes in dietary carbohydrate and Na loads.

Divergent phenotypic patterns and commitment to apoptosis of Caco-2 cells during spontaneous and butyrate-induced differentiation.

Caco-2 cells differentiate spontaneously when cultured in confluence and on exposure to the physiologically relevant short-chain fatty acid, butyrate. This study aimed to compare the phenotype induced by these pathways and their relations to cell turnover. Caco-2 cells were treated with butyrate at a nontoxic concentration of 2 mM for 3 days, or allowed to spontaneously differentiate for 0-21 days. Brush border hydrolase activities and carcinoembryonic antigen (CEA) expression, transepithelial resistance and dome formation, expression of components of the urokinase system, and cell turnover by flow cytometry, and the degree of DNA fragmentation were quantified. Butyrate induced increases in alkaline phosphatase activity and CEA expression but not the activities of other hydrolases, while culture alone induced progressive increases in the activities/expression of all markers. Butyrate induced a significantly greater increase in transepithelial resistance (TER) than occurred during culture alone but the densities of domes were similar. Butyrate induced a ninefold increase in urokinase receptor expression and twofold increase in urokinase activity, while culture alone induced a significantly smaller increase in receptor expression, an increase in plasminogen activator inhibitor-1 but no change in activity. While both stimuli induced cell cycle arrest, only butyrate increased the proportion of cells undergoing apoptosis. In conclusion, differentiation of Caco-2 cells can proceed along multiple pathways but does not necessarily lead to apoptosis. The phenotypic changes during spontaneous differentiation mimic those that occur in normal colonic epithelial cells in vivo during their migration from the crypt base to neck, while butyrate-induced effects more closely follow those occurring when normal colonic epithelial cells migrate from crypt neck to the surface compartment.

Effect of butyrate on paracellular permeability in rat distal colonic mucosa ex vivo.

The effects of butyrate on colonic epithelial barrier function are poorly understood. The aim of this study was to examine the short-term effects of butyrate on paracellular permeability of rat distal colonic epithelium. Mucosa mounted in Ussing chambers was treated with butyrate (1-10 mmol/L) for 4 h. Transepithelial conductance, [51Cr]-EDTA flux, mucosal brush border hydrolase activity and epithelial kinetics, using proliferating cell nuclear antigen (PCNA) staining, were measured. On exposure to butyrate (10 mmol/L, but not 1 or 5 mmol/L), transepithelial conductance was 65 +/- 2% higher (mean +/- SEM; n = 8, P < 0.05, paired t-test) and the rate coefficient for [51Cr]-EDTA flux was 65 +/- 25% higher (P = 0.03) than those of control tissue. Histologically, the epithelium exhibited no signs of injury, but butyrate-treated tissue exhibited interstitial oedema consistent with water uptake in association with butyrate absorption. Butyrate caused a reduction in crypt column height to 30.6 +/- 1.6 cells from 33.4 +/- 1.8 cells in controls (n = 10, P < 0.03), but the number of cells per crypt column staining with PCNA was unchanged. Butyrate significantly reduced the mucosal activities of alkaline phosphatase by 40 +/- 16%, maltase by 54 +/- 12% and dipeptidyl peptidase IV by 41 +/- 14%. Acute exposure to butyrate increased paracellular permeability in rat distal colon. The mechanism involved may relate to the loss of differentiated surface epithelial cells, or as a physiological response to Na+-coupled butyrate uptake.

Relationship of hydrolase activities to epithelial cell turnover in distal colonic mucosa of normal rats.

The relationships between changes induced by diet in colonic epithelial kinetics and in the activities of brush border hydrolases are poorly defined. The aims of this study are to define these relationships, as changes in kinetics would be expected to influence differentiation, and to determine whether the type of ingested dietary indigestible carbohydrates influences hydrolase activities. Groups of eight rats were fed a low fibre diet +/- supplements of different types of indigestible carbohydrates for 4 weeks. Alkaline phosphatase (ALP) and dipeptidyl peptidase IV (DPPIV) activities and epithelial kinetics were measured in distal colonic mucosa. Median ALP activities correlated positively and DPPIV activity negatively with the median proportion of cells entering metaphase (r = 0.58 and -0.58, respectively; P < 0.05) and number of metaphase arrests per crypt column across the diets (r = 0.59 and 0.58, respectively; P < 0.05). Stepwise regression analysis showed that both hydrolases independently predicted these kinetic indices (R2 > 63% for each). Mucosal ALP activities were markedly elevated during consumption of raw potato starch, guar gum and methylcellulose, while only potato starch caused a significant elevation of DPPIV activities. The type of indigestible carbohydrate in the diet influences colonic mucosal hydrolase activities. The opposite relationship between kinetics and each of the two hydrolases indicates that these hydrolases do not reflect the same event; dipeptidyl peptidase IV might relate to differentiation status while ALP could also be influenced by epithelial irritation due to changes in luminal conditions.

Modulation of distal colonic epithelial barrier function by dietary fibre in normal rats

BACKGROUNDDietary fibre influences the turnover and differentiation of the colonic epithelium, but its effects on barrier function are unknown.AIMSTo determine whether altering the type and amount of fibre in the...

Insulin Modulates Cellular Proliferation in Developing Human Jejunum and Colon

Several lines of evidence suggest an important role for insulin in the regulatory mechanism of rodent small intestinal development. To investigate its potential implication in human gut, the immunofluorescent localization of insulin receptors (IR) and the influence of insulin (30 µU or 3 mU/ml) on [³H]-thymidine incorporation and on lactase and alkaline phosphatase activities were studied in fetal jejunum and colon (14–19 weeks). We demonstrate the early presence of IR, mainly detected in the basolateral portion of enterocytes and colonocytes along the crypt-villus axis. Insulin increased [³H]-thymidine incorporation as well as epithelial labeling indices in cultured explants from jejunum and colon without affecting enzymic activities. This study establishes, for the first time, that insulin stimulates proliferation of epithelial cells expressing IR in both segments without affecting brush border hydrolases in the developing human gut.

Ontogeny of EGF receptors in the human gut.

Epidermal growth factor and related substances mediate their effects on epithelial cells through binding to high-affinity receptors (EGF-R) at their basolateral surface and it is hypothesized that this growth factor system play a major role in gut morphogenesis and maintenance. The current review emphasizes on analyzing the expression and the biochemical characteristics of EGF-R in human fetal gut segments and correlating the biological actions of EGF-R ligands. They appear to be primarily involved in the local regulation of epithelial cell proliferation in which EGF-R are abundant. Alternatively, EGF-R ligands exert some precocious maturative effects by increasing intestinal lactase activity and decreasing brush border hydrolases in colon while they down modulate the expression of segment-specific markers of terminal differentiation such as sucrase, trehalase and glucoamylase in the intestine and chief cell lipase in the stomach. Such effects are consistent with the identification of receptors at the surface of all epithelial cell types, illustrating the modulatory role of EGF on differentiated gut epithelial cells. Comparison with animal models illustrates similar biochemical properties of receptors and underlines physiological aspects specific to human gut development. The relevance for ligand heterogeneity is also discussed and tentatively associated with different delivery pathways or physiological responses.

A pancreatic extract-enriched diet corrects ileal mucosa atrophy in endotoxemic aged rats.

An altered adaptive response of the pancreas and small intestine to nutritional stress has an adverse impact upon nutritional status in elderly humans or senescent rats. We evaluated the effects of a pancreatic extract nutritional supplement on intestinal mucosa adaptation in LPS-treated aged rats. Endotoxemic rats were starved for 48 hr and then refed ad libitum for four days with a standard diet. Afterwards they received, over one week, the standard diet enriched with either pancreatic extract (PE) (2.4 g/day) or casein (isonitrogenous to PE supplement). Healthy aged rats fed ad libitum with a standard diet were studied in parallel. Whereas no changes occurred in the jejunal segment, an adaptive villus hyperplasia was observed in the proximal ileum of rats receiving PE without an increase in the brush border hydrolase activities. Our results indicate that oral PE supplementation exerts a trophic effect on the ileal mucosa of aged rats in response to nutritional stress.