The expression of lactase enzymatic activity and mRNA in human fetal jejunum. Effect of organ culture and of treatment with hydrocortisone

Single-course antenatal corticosteroids is related to faster growth in very-low-birth-weight infant

BACKGROUND

Antenatal corticosteroids (ACS) treatment is critical to support survival and lung maturation in preterm infants, however, its effect on feeding and growth is unclear. Prior preterm delivery, it remains uncertain whether ACS treatment should be continued if possible (repeated course ACS), until a certain gestational age is reached. We hypothesized that the association of single-course ACS with feeding competence and postnatal growth outcomes might be different from that of repeated course ACS in very-low-birth-weight preterm infants.

METHODS

A multicenter retrospective cohort study was conducted in very-low-birth-weight preterm infants born at 23-37 weeks' gestation in South China from 2011 to 2014. Data on growth, nutritional and clinical outcomes were collected. Repeated course ACS was defined in this study as two or more courses ACS (more than single-course). Infants were stratified by gestational age (GA), including GA < 28 weeks, 28 weeks ≤ GA < 32 weeks and 32 weeks ≤ GA < 37 weeks. Multiple linear regression and multilevel model were applied to analyze the association of ACS with feeding and growth outcomes.

RESULTS

A total of 841 infants were recruited. The results, just in very-low-birth-weight preterm infants born at 28-32 weeks' gestation, showed both single and repeated course of ACS regimens had shorter intubated ventilation time compared to non-ACS regimen. Single-course ACS promoted the earlier application of amino acid and enteral nutrition, and higher rate of weight increase (15.71; 95%CI 5.54-25.88) than non-ACS after adjusting for potential confounding factors. No associations of repeated course ACS with feeding, mean weight and weight increase rate were observed.

CONCLUSIONS

Single-course ACS was positively related to feeding and growth outcomes in very-low-birth-weight preterm infants born at 28-32 weeks' gestation. However, the similar phenomenon was not observed in the repeated course of ACS regimen.

Nutritional programming by glucocorticoids in breast milk: Targets, mechanisms and possible implications

Vertical transmission of glucocorticoids via breast milk might pose a mechanism through which lactating women could prepare their infants for the postnatal environment. The primary source of breast-milk glucocorticoids is probably the systemic circulation. Research from our group showed that milk cortisol and cortisone concentrations follow the diurnal rhythm of maternal hypothalamus-pituitary-adrenal axis activity, with a higher abundance of cortisone compared to cortisol. Measurement of breast-milk glucocorticoid concentrations is challenging due to possible cross-reactivity with progestagens and sex steroids, which are severely elevated during pregnancy and after parturition. This requires precise methods that are not hindered by cross reactivity, such as LC-MS/MS. There are some data suggesting that breast-milk glucocorticoids could promote intestinal maturation, either locally or after absorption into the systemic circulation. Breast-milk glucocorticoids might also have an effect on the intestinal microbiome, although this has not been studied thus far. Findings from studies investigating the systemic effects of breast-milk glucocorticoids are difficult to interpret, since none took the diurnal rhythm of glucocorticoids in breast milk into consideration, and various analytical methods were used. Nevertheless, glucocorticoids in breast milk might offer a novel potential pathway for signal transmission from mothers to their infants.

Feeding tolerance of preterm infants appropriate for gestational age (AGA) as compared to those small for gestational age (SGA)

Preterm infants are often considered too unstable to be fed enterally so they are exposed to complications related to a prolonged enteral fasting. Our study aims to compare feeding tolerance of adequate for gestational age (AGA) versus small for gestational age (SGA) infants and to evaluate which perinatal factors affect feeding tolerance (measured as time to achieve full enteral feeding, FEF). Inborn infants with a gestational age (GA) less than 32 weeks, born from January 2006 to December 2010, were eligible for this study. We enrolled 310 infants. The time to FEF was longer for SGA infants than for AGA, while a longer GA was associated to a reduced time to FEF. A beneficial effect was observed for antenatal steroids, while Apgar score below 7, the administration of inotrops or caffeine, the occurrence of sepsis or NEC and the presence of PDA were associated to a longer time to FEF. When evaluated jointly with a multivariate analysis, GA (p < 0.0001), antenatal steroids prophylaxis (p = 0.002), SGA (p < 0.0001) and occurrence of NEC (p = 0.0002) proved to have independent prognostic impact on the time to FEF. Feeding tolerance is better as GA increases, and worsen in SGA infants. Antenatal betamethasone is effective in reducing the time to FEF in both AGA and SGA.

Ontogeny, growth and development of the small intestine: Understanding pediatric gastroenterology

Throughout our lifetime, the intestine changes. Some alterations in its form and function may be genetically determined, and some are the result of adaptation to diet, temperature, or stress. The critical period programming of the intestine can be modified, such as from subtle differences in the types and ratios of n3:m6 fatty acids in the diet of the pregnant mother, or in the diet of the weanlings. This early forced adaptation may persist in later life, such as the unwanted increased intestinal absorption of sugars, fatty acids and cholesterol. Thus, the ontogeny, early growth and development of the intestine is important for the adult gastroenterologist to appreciate, because of the potential for these early life events to affect the responsiveness of the intestine to physiological or pathological challenges in later life.

Hydrocortisone modulates cholera toxin endocytosis by regulating immature enterocyte plasma membrane phospholipids

BACKGROUND & AIMS

Diarrheal disease is a major cause of morbidity and mortality in infants and children worldwide. Evidence has indicated immature human enterocytes and their interaction with bacteria and enterotoxins may account for the noted increased susceptibility of neonates to diarrhea. Our aim was to characterize the developmental difference in cholera toxin (CT)-GM1-mediated endocytosis.

METHODS

We used H4 cells (a fetal human small intestinal epithelial cell line), T84 cells, primary cultured mature human small intestinal epithelial cells, and human fetal small intestine xenografts. In addition, hydrocortisone was used as a potent intestinal trophic factor to induce maturation of the human enterocytes.

RESULTS

Here we show an increase in CT-caveolae and a decrease in CT-clathrin colocalization in H4/hydrocortisone compared with H4 cells by electron microscopy. In T84 and freshly isolated human small intestinal epithelial cells, a significant amount of GM1 was partitioned into the lipid rafts. In contrast, there was little CT-GM1/lipid raft association in H4 cells. However, hydrocortisone significantly increased GM1/lipid raft association in H4 cells. Furthermore, we noted an increase in the level of phosphatidylcholine, sphingomyelin, and the ratio of phosphatidylcholine/phosphatidylinositol in mature compared with immature enterocytes and that hydrocortisone can accelerate this maturational process. Disruption of phosphatidylinositol transfer protein alpha using small interference RNA showed an increase in GM1/lipid raft association in H4 cells and resulted in a decreased CT response.

CONCLUSIONS

Our studies suggest that the developmental change in CT endocytosis is partially caused by an increased GM1-lipid raft association through a maturational change of phospholipid composition on the cell surface of immature enterocytes.

Hormone induced expression of brush border lactase in suckling rat intestine

The postnatal development of intestine is associated with a decline in brush border lactase activity in rodents. This is similar to adulthood hypolactasia, a phenomenon prevalent in humans worldwide. In the present study, the effect of luminal proteases from adult rat intestine was studied in vitro on intestinal lactase activity in saline control, thyroxine, insulin and cortisone treated rat pups. Lactase levels were determined by enzyme analysis and Western blotting. mRNA levels encoding lactase were determined by Northern blotting. Administration of thyroxine for 4 days reduced (P<0.05) lactase activity, but insulin treatment had no effect in 8-day-old rat intestine. However, cortisone administration augmented (P<0.01) lactase activity, under these conditions. Western blot analysis showed decreased lactase signal corresponding to 220-kDa protein band in thyroxine treated animals. However, the intensity of lactase signal was high in cortisone treated animals compared to controls. mRNA levels encoding lactase showed a 6.8-kb mRNA transcript in saline and hormone treated rats. mRNA levels encoding lactase were increased in cortisone treated animals but were reduced in thyroxine injected pups compared to controls. Microvillus membranes from saline (P<0.01) and thyroxine (P<0.05) or insulin (P<0.01) treated rats upon incubation with luminal wash from adult rat intestine showed a significant decline in lactase activity. These findings suggest that thyroxine, insulin or cortisone induced changes in lactase expression in suckling rat intestine make it susceptible to luminal proteases, which may in part be responsible for observed maturational decline in lactase activity in adult rat intestine.

An NSP4-dependant mechanism by which rotavirus impairs lactase enzymatic activity in brush border of human enterocyte-like Caco-2 cells

Lactase-phlorizin hydrolase (LPH, EC 3.2.1.23-62) is a brush border membrane (BBM)-associated enzyme in intestinal cells that hydrolyse lactose, the most important sugar in milk. Impairing in lactase activity during rotavirus infection has been described in diseased infants but the mechanism by which the functional lesion occurs remains unknown. We undertook a study to elucidate whether rotavirus impairs the lactase enzymatic activity in BBM of human enterocyte cells. In this study we use cultured human intestinal fully differentiated enterocyte-like Caco-2 cells to demonstrate how the lactase enzymatic activity at BBM is significantly decreased in rhesus monkey rotavirus (RRV)-infected cells. We found that the decrease in enzyme activity is not dependent of the Ca(2+)- and cAMP-dependent signalling events triggered by the virus. The LPH biosynthesis, stability, and expression of the protein at the BBM of infected cells were not modified. We provide evidence that in RRV-infected cells the kinetic of lactase enzymatic activity present at the BBM was modified. Both BBM(control) and BBM(RRV) have identical K(m) values, but hydrolyse the substrate at different rates. Thus, the BBM(RRV) exhibits almost a 1.5-fold decreased V(max) than that of BBM(control) and is therefore enzymatically less active than the latter. Our study demonstrate conclusively that the impairment of lactase enzymatic activity at the BBM of the enterocyte-like Caco-2 cells observed during rotavirus infection results from an inhibitory action of the secreted non-structural rotavirus protein NSP4.

In vitro translation of RNA to lactase during postnatal development of rat intestine

mRNA levels encoding lactase were detected by Northern blot analysis using two different probes in developing rat intestine. Probe I and probe II corresponding to second half of prolactase gene showed a 6.8 kb mRNA transcript in 7, 14, 21 and 30 day old rat intestine. There was no change in quantity of lactase mRNA detected using probe II, but hybridization with probe I showed a progressive decrease in mRNA transcript encoding lactase with age. At day 7 and 14 of postnatal development, the lactase mRNA was quite high, but it reduced upon weaning. The in vitro translation products of RNA detected by Western blot analysis using brush border lactase antibodies showed several isoforms of lactase antigen with molecular weight ranging from 100-220 kDa. Analysed at days 7 and 30 of postnatal development, lactase isoforms of molecular weight 130 kDa and 220 kDa were similar to those found in purified brush border membranes. The translation of RNA to 220 kDa lactase protein was high in 7 and 14 day old pups, but it was markedly reduced in 30 day old animals. These findings support the contention that translation of mRNA to lactase is impaired in weaned animals, which may also be responsible for the maturational decline in lactase activity in adult rat intestine.

The effect of antenatal corticosteroids on gut peptides of preterm infants--a matched group comparison: corticosteroids and gut development

BACKGROUND

Postnatal glucocorticosteroid administration has trophic effects on the gastrointestinal tract of preterm infants. The aim of the present study was to investigate whether antenatal glucocorticosteroids affect the secretion of gastrointestinal peptides that are involved in the regulation of secretion, motility and mucosal protection of the gastrointestinal tract.

METHODS

Plasma levels of gastrin, motilin and vasoactive intestinal peptide (VIP) were estimated in 28 preterm infants with a mean birth weight of 1280 g, and mean gestational age of 30.5 weeks, whose mothers had received a full course of antenatal glucocorticosteroids (GC group) and in 17 preterm infants with mean birth weight of 1200 g, mean gestational age of 30.2 weeks, whose mothers had not received corticosteroids (control group). GI peptides were estimated on two occasions: (a) Immediately after birth and (b) following the initiation of enteral feeding.

RESULTS

Gastrin levels in the GC group were significantly higher both immediately after birth (early measurement) and also after receiving enteral feeding (late measurement) (p<0.001, p<0.05, respectively) but the increase in plasma gastrin concentration was identical in both groups (32 vs. 33 pg/ml). Motilin levels in the GC group were also significantly higher as compared to the control group but only in the late measurement (p<0.001). Gastrin and motilin levels in both groups were significantly higher in the late measurement as compared to the early measurement (GC group: p<0.001, p<0.001, respectively;

CONTROLS

p<0.001, p<0.01, respectively). There was no significant difference in VIP levels between the two groups both in the early and the late measurements.

CONCLUSION

Antenatal glucocorticoids (GCs) stimulate gastrin secretion in the fetus but not in the neonate. Contrary to this, corticosteroid effect on motilin is seen only postnatally following the introduction of enteral feeding. Glucocorticosteroids appear to have no effect on VIP levels. Plasma gastrin and motilin levels increase significantly following the introduction of enteral feeding regardless of the use of steroids.

Normal and glucocorticoid-induced development of the human small intestinal xenograft

The aim of this study was to determine whether intestinal xenografts could recapitulate human in utero development by using disaccharidases as markers. Twenty-week-old fetal intestine was transplanted into immunocompromised mice and was followed. At 20-wk of gestation, the fetal human intestine was morphologically developed with high sucrase and trehalase but had low lactase activities. By 9-wk posttransplantation, jejunal xenografts were morphologically and functionally developed and were then monitored for </=6 mo. Both sucrase and trehalase activities remained unchanged, but lactase activity increased in a manner similar to that described in in utero development. Changes in sucrase and lactase activities were paralleled by protein levels. Cortisone acetate treatment at 20-wk posttransplantation accelerated the ontogeny of lactase but did not alter sucrase and trehalase activities. Biopsies from 1- and 2-yr-old infant intestine showed that all activities, except trehalase in the proximal intestine, corresponded to the levels found in jejunal xenografts at 24 wk posttransplantation. These studies suggest that 20-wk-old fetal intestine has the extrauterine developmental potential to follow normal intrauterine ontogeny as a xenograft.

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.

Development of glucocorticoid-responsiveness in mouse intestine

There are conflicting data from human studies regarding the ability of exogenous glucocorticoids to stimulate maturation of the small intestine. The discrepancies may relate to differences in hormone doses and age administered. To explore this general concept, we have used a mouse model to determine intestinal responsiveness to dexamethasone (DEX) at various times during development. We first showed that trehalase mRNA is a sensitive marker of intestinal maturation in the mouse; being undetectable (by Northern blotting) in the prenatal period, expressed at low levels during the first 2 postnatal weeks and then displaying a marked increase in the 3rd postnatal week. DEX was unable to elicit detectable trehalase mRNA in fetal mice, but caused significant increases in the postnatal period. The use of a range of DEX doses (0.0125-2.5 nmol/g BW per day) established that there is no change in sensitivity between the 1st and 2nd postnatal weeks, but there is a significant increase in maximal responsiveness of trehalase mRNA to the hormone. Similar results were obtained when sucrase-isomaltase mRNA was assayed in the same animals. Thus, in this rodent model, there appears to be at least three phases in the DEX responsiveness of the developing intestine: an early phase (prenatal) when DEX is unable to elicit intestinal maturation; then a phase (first postnatal week) of modest responsiveness; then a transition to increased responsiveness. These findings point to the need for careful attention to dose and age in analyses of glucocorticoid effects in human infants.

Ontogeny of intestinal nutrient transport

Children born prematurely lack the ability to digest and to absorb nutrients at rates compatible with their nutritional needs. As a result, total parenteral nutrition may need to be given. While this nutritional support may be life-saving, the baby who receives this therapy is exposed to the risks of possible sepsis, catheter dysfunction, and liver disease. The rodent model of postnatal development provides a useful framework to investigate some of the cellular features of human intestinal development. The up-regulation of intestinal gene expression and precocious development of intestinal nutrient absorption can be achieved by providing growth factor(s) or by modifying the composition of the maternal diet during pregnancy and nursing or the weaning diet of the infant. Accelerating the digestive and absorptive functions of the intestine would thereby allow for the maintenance of infant nutrition through oral food intake, and might possibly eliminate the need for, and risks of, total parenteral nutrition. Accordingly, this review was undertaken to focus on the adaptive processes available to the intestine, to identify what might be the signals for and mechanisms of the modified nutrient absorption, and to speculate on approaches that need to be studied as means to possibly accelerate the adaptive processes in ways which would be beneficial to the newborn young.Key words: absorption, adaptation, diet, peptides.

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.

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 microU 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.

The expression of epidermal growth factor and transforming growth factor-alpha mRNA in the small intestine of suckling rats: organ culture study

Epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) are associated with regulation of various gastrointestinal functions. In order to better understand their role in developing small intestine EGF, TGF-alpha and EGF-R steady-state mRNA levels and transcript stability were determined. Reverse transcription (RT) competitive-polymerase chain reaction (PCR) revealed that intestinal TGF-alpha mRNA levels were 10-fold higher in comparison with EGF mRNA. The primary intestinal culture technique was used to evaluate mRNA stability. The stability of TGF-alpha mRNA was remarkably lower than the stability of EGF mRNA. High levels of TGF-alpha mRNA accompanied by high degradation rate of this mRNA suggested a rapid turnover of intestinal TGF-alpha mRNA.

Selective effects of hydrocortisone on intestinal lipoprotein and apolipoprotein synthesis in the human fetus

Studies employing human fetal intestine have yielded much interesting information on the role of polarized enterocytes in fat absorption and transport. Using the organ culture model, we examined the influence of hydrocortisone on the synthesis and secretion of lipids and lipoproteins. Human jejunal explants were cultured for 5 days at 37 degrees C in serum-free medium containing either [14C]-oleic acid or [14C]-acetate, alone or supplemented with hydrocortisone (25 or 50 ng/ml). The uptake of [14C]-oleic acid was associated with the production of triglycerides, phospholipids, and cholesteryl esters, which were all affected by hydrocortisone. This hormonal agent (50 micrograms) led to the marked reduction of secreted triglycerides (43%, P < 0.01), phospholipids (39%, P < 0.01), and cholesteryl esters (36%, P < 0.05) without altering the characteristic distribution of tissue and medium lipid classes. Similarly, hydrocortisone significantly (P < 0.01) decreased (approximately 60%) the incorporation of [14C]-acetate into secreted free and esterified cholesterol in the medium. With [14C]-oleic acid as a precursor, hydrocortisone significantly diminished the delivery of chylomicrons and very low density lipoproteins to the medium while consistently enhancing the secretion of high density lipoproteins. In parallel, [35S]-methionine pulse-labeling of jejunal explants revealed the concomitant inhibitory effect of hydrocortisone on apo B-100 synthesis and hydrocortisone's stimulatory effect on apo B-48 and apo A-1. These studies suggest that glucocorticoids play a critical role in lipoprotein processing during intestinal development.

Glucocorticoid receptors immunoreactivity in tissue of human embryos

The exact period when glucocorticoid receptors (GR) appear in human embryos is unknown, however their presence is acknowledged in target tissues before the fetal adrenal cortex secretes cortisol. Determining when GR develop could serve as an index of the importance of glucocorticoids in the morphological and functional development of tissues. The aim of this study was to determine time of onset of GR in human tissues using an immunohistochemical method. Results indicate GR are present in tissues of 8-10-week-old human embryos: in most tissues, the immune reaction was only or predominantly nuclear.

Intestinal brush border glycohydrolases: structure, function, and development

The hydrolytic enzymes of the intestinal brush border membrane are essential for the degradation of nutrients to absorbable units. Particularly, the brush border glycohydrolases are responsible for the degradation of di- and oligosaccharides into monosaccharides, and are thus crucial for the energy-intake of humans and other mammals. This review will critically discuss all that is known in the literature about intestinal brush border glycohydrolases. First, we will assess the importance of these enzymes in degradation of dietary carbohydrates. Then, we will closely examine the relevant features of the intestinal epithelium which harbors these glycohydrolases. Each of the glycohydrolytic brush border enzymes will be reviewed with respect to structure, biosynthesis, substrate specificity, hydrolytic mechanism, gene regulation and developmental expression. Finally, intestinal disorders will be discussed that affect the expression of the brush border glycohydrolases. The clinical consequences of these enzyme deficiency disorders will be discussed. Concomitantly, these disorders may provide us with important details regarding the functions and gene expression of these enzymes under specific (pathogenic) circumstances.

Development of human intestinal and gastric enzymes

In humans as opposed to rodents development of the gastrointestinal tract is much less coordinated with functional changes occurring at different times during the fetal period. This article reviews developmental patterns of intestinal brush border enzymes, lysosomal enzymes, peroxisomal enzymes and de novo synthesis of intestinal lipoproteins. It also describes the developmental patterns of gastric lipase and pepsin during early fetal life. Data are presented on the most recent observations related to the regulatory mechanisms in the development of human intestinal brush border hydrolases. A clearer understanding of the ontogeny and of the regulatory mechanism of the functional development of the gastrointestinal tract will enable researchers and clinicians to improve nutritional support in a fashion appropriate for the digestive and metabolic capabilities of an infant at any developmental stage.

Induction of lactase biosynthesis in the human intestinal epithelial cell line Caco-2

The human colonic adenocarcinoma cell line Caco-2 forms monolayers of differentiated enterocyte-like cells when cultured on permeable supports. After confluency, Caco-2 cells express a number of brush-border enzymes including lactase-phlorizin hydrolase, sucrase-isomaltase and dipeptidylpeptidase IV. We have studied, with particular emphasis on lactase-phlorizin hydrolase, the modulation of biosynthesis of these enzymes by stimulating second messenger systems. Forskolin induced lactase-phlorizin hydrolase synthesis approximately fourfold within 7 h, suppressed sucrase-isomaltase synthesis, and had little effect on dipeptidylpeptidase IV. Dibutyryl-cAMP, 8-bromo-cAMP and vasoactive intestinal peptide also increased lactase-phlorizin hydrolase biosynthesis, indicating c-AMP dependent regulation. The induction of lactase-phlorizin hydrolase biosynthesis could be inhibited by actinomycin D and was preceded by a fourfold increase in lactase-phlorizin hydrolase mRNA levels, suggesting transcriptional control. Phorbol 12-myristate 13-acetate had an inhibitory effect on brush-border enzyme synthesis, in particular on sucrase-isomaltase, and blocked the forskolin-induced biosynthesis of lactase-phlorizin hydrolase. Lactase-phlorizin hydrolase synthesis was also inducible by hydrocortisone, but maximal induction required at least 3 days during which time sucrase-isomaltase synthesis diminished. The results indicate opposite regulation of lactase-phlorizin hydrolase and sucrase-isomaltase via cAMP and corticosteroids, and suggest that the Caco-2 cell line can serve as a model system to study aspects of the humoral regulation of human intestinal brush-border enzymes in cell culture.

Maturation of human fetal stomach in organ culture

BACKGROUND

This investigation was undertaken to establish a serum-free organ culture technique allowing for the morphological and physiological maintenance of human fetal stomach in vitro.

METHODS

Explants from gastric corpuses (12-17 weeks of gestation) were cultured in serum-free medium for periods of up to 15 days.

RESULTS

After 15 days of culture, surface mucous cells were more mature, gastric glands were numerous and well developed, and all epithelial cell types were morphologically very well preserved. Morphometric measurements of the glands revealed an accelerated development in culture compared with that found in utero. Even though the incorporation of [3H]thymidine into total DNA decreased, the labeling indices determined by radioautography confirmed that epithelial cell proliferation was maintained especially in the pit/neck portion and at the base of the glandular compartments. A significant increase in total glycoprotein synthesis, as evaluated by the incorporation of [3H]glucosamine, was observed and correlated with the differentiation of the mucous cells.

CONCLUSIONS

This investigation establishes for the first time that human gastric mucosa can be maintained up to 15 days in organ culture and that maturation of the gastric mucosa can be reproduced in chemically defined media.

The levels of lactase and of sucrase-isomaltase along the rabbit small intestine are regulated both at the mRNA level and post-translationally

We determined along the small intestine of young and adult rabbits the activities of lactase (LPH) and sucrase (SI), the levels of their cognate mRNAs, and examined the in vitro biosynthesis of LPH and pro-SI. Lactase activity is low in the proximal 1/3 of the intestine, whereas the mRNA levels are high. However, the rates of biosynthesis of the LPH forms correlated well with the steady-state levels of LPH mRNA in all segments, indicating that factor(s) acting post-translationally produce a decline in brush border LPH in the proximal small intestine. These factor(s) are not involved in the processing of pro-LPH to mature LPH, since the relative amounts of the various forms of LPH are almost the same along the small intestine. Unexpectedly, we find that also for SI the ratio of activity to mRNA is low in proximal intestine. The biosynthesis of pro-SI correlates with the steady-state levels of its mRNA. Hence, the steady-state levels of LPH and SI along the small intestine are regulated both by mRNA levels and by posttranslational factor(s).