Maturation of sucrase-isomaltase complex in human fetal small and large intestine during gestation

Genetic and acquired sucrase-isomaltase deficiency: A clinical review

Genetic sucrase-isomaltase deficiency (GSID) is an inherited deficiency in the ability to digest sucrose and potentially starch due to mutations in the sucrase-isomaltase (SI) gene. Congenital sucrase-isomaltase deficiency is historically considered to be a rare condition affecting infants with chronic diarrhea as exposure to dietary sucrose begins. Growing evidence suggests that individuals with SI variants may present later in life, with symptoms overlapping with those of irritable bowel syndrome. The presence of SI genetic variants may, either alone or in combination, affect enzyme activity and lead to symptoms of different severity. As such, a more appropriate term for this inherited condition is GSID, with a recognition of a spectrum of severity and onset of presentation. Currently, disaccharidase assay on duodenal mucosal tissue homogenates is the gold standard in diagnosing SI deficiency. A deficiency in the SI enzyme can be present at birth (genetic) or acquired later, often in association with damage to the enteric brush-border membrane. Other noninvasive diagnostic alternatives such as sucrose breath tests may be useful but require further validation. Management of GSID is based on sucrose and potentially starch restriction tailored to the individual patients' tolerance and symptoms. As this approach may be challenging, additional treatment with commercially available sacrosidase is available. However, some patients may require continued starch restriction. Further research is needed to clarify the true prevalence of SI deficiency, the pathobiology of single SI heterozygous mutations, and to define optimal diagnostic and treatment algorithms in the pediatric population.

Effects of Early Life Oral Arsenic Exposure on Intestinal Tract Development and Lipid Homeostasis in Neonatal Mice: Implications for NAFLD Development

BACKGROUND

Newborns can be exposed to inorganic arsenic (iAs) through contaminated drinking water, formula, and other infant foods. Epidemiological studies have demonstrated a positive association between urinary iAs levels and the risk of developing nonalcoholic fatty liver disease (NAFLD) among U.S. adolescents and adults.

OBJECTIVES

The present study examined how oral iAs administration to neonatal mice impacts the intestinal tract, which acts as an early mediator for NAFLD.

METHODS

Neonatal mice were treated with a single dose of iAs via oral gavage. Effects on the small intestine were determined by histological examination, RNA sequencing, and biochemical analysis. Serum lipid profiling was analyzed by fast protein liquid chromatography (FPLC), and hepatosteatosis was characterized histologically and biochemically. Liver X receptor-alpha (LXR α ) knockout (L x r α - / - ) mice and liver-specific activating transcription factor 4 (ATF4)-deficient (A t f 4 Δ H e p ) mice were used to define their roles in iAs-induced effects during the neonatal stage.

RESULTS

Neonatal mice exposed to iAs via oral gavage exhibited accumulation of dietary fat in enterocytes, with higher levels of enterocyte triglycerides and free fatty acids. These mice also showed accelerated enterocyte maturation and a longer small intestine. This was accompanied by higher levels of liver-derived very low-density lipoprotein and low-density lipoprotein triglycerides, and a lower level of high-density lipoprotein cholesterol in the serum. Mice exposed during the neonatal period to oral iAs also developed hepatosteatosis. Compared with the control group, iAs-induced fat accumulation in enterocytes became more significant in neonatal L x r α - / - mice, accompanied by accelerated intestinal growth, hypertriglyceridemia, and hepatosteatosis. In contrast, regardless of enterocyte fat accumulation, hepatosteatosis was largely reduced in iAs-treated neonatal A t f 4 Δ H e p mice.

CONCLUSION

Exposure to iAs in neonatal mice resulted in excessive accumulation of fat in enterocytes, disrupting lipid homeostasis in the serum and liver, revealing the importance of the gut-liver axis and endoplasmic reticulum stress in mediating iAs-induced NAFLD at an early age. https://doi.org/10.1289/EHP12381.

In vitro models of gut digestion across childhood: current developments, challenges and future trends

The human digestion is a multi-step and multi-compartment process essential for human health, at the heart of many issues raised by academics, the medical world and industrials from the food, nutrition and pharma fields. In the first years of life, major dietary changes occur and are concomitant with an evolution of the whole child digestive tract anatomy and physiology, including colonization of gut microbiota. All these phenomena are influenced by child exposure to environmental compounds, such as drugs (especially antibiotics) and food pollutants, but also childhood infections. Due to obvious ethical, regulatory and technical limitations, in vivo approaches in animal and human are more and more restricted to favor complementary in vitro approaches. This review summarizes current knowledge on the evolution of child gut physiology from birth to 3 years old regarding physicochemical, mechanical and microbial parameters. Then, all the available in vitro models of the child digestive tract are described, ranging from the simplest static mono-compartmental systems to the most sophisticated dynamic and multi-compartmental models, and mimicking from the oral phase to the colon compartment. Lastly, we detail the main applications of child gut models in nutritional, pharmaceutical and microbiological studies and discuss the limitations and challenges facing this field of research.

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.

Sucrase-Isomaltase Expression in Dysplasia Associated With Barrett's Esophagus and Chronic Gastritis

Aberrant cytoplasmic sucrase-isomaltase has been detected in colonic neoplasia, including dysplasia in ulcerative colitis. We investigated expression by immunostaining in 28 cases of Barrett's esophagus and 67 cases of chronic gastritis. Staining location (membrane or cytoplasmic) and percent positivity (< 1% = 0; 1-50% = 1+; > 50% = 2+) were record ed. Fifteen cases with Barrett's esophagus were negative for dysplasia, 1 was indefinite, and 12 were positive. All demonstrated surface membrane staining, while 2 of the 15 neg ative (1+) cases, 0 of the 1 indefinite case, and 11 of the 12 dysplastic (2+ in 7) cases revealed cytoplasmic positivity (P < .001). In chronic gastritis (23 were negative, 5 were indefinite, and 39 were positive) all revealed surface membrane staining, whereas cyto plasmic positivity was present in 1 of 23 negative (1+) cases, 1 of 5 indefinite cases, and 37 of 39 dysplastic (2+ in 18) cases (P < .001). In Barrett's esophagus and chronic gastri tis, cytoplasmic sucrase-isomaltase expression strongly correlates with the presence of dys plasia. Int J Surg Pathol 2(4).-281-286, 1995

Intestinal mucosal atrophy and adaptation

Mucosal adaptation is an essential process in gut homeostasis. The intestinal mucosa adapts to a range of pathological conditions including starvation, short-gut syndrome, obesity, and bariatric surgery. Broadly, these adaptive functions can be grouped into proliferation and differentiation. These are influenced by diverse interactions with hormonal, immune, dietary, nervous, and mechanical stimuli. It seems likely that clinical outcomes can be improved by manipulating the physiology of adaptation. This review will summarize current understanding of the basic science surrounding adaptation, delineate the wide range of potential targets for therapeutic intervention, and discuss how these might be incorporated into an overall treatment plan. Deeper insight into the physiologic basis of adaptation will identify further targets for intervention to improve clinical outcomes.

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.

Differential expression of claudin-2 along the human intestine: Implication of GATA-4 in the maintenance of claudin-2 in differentiating cells

Claudins, and particularly claudin-2, are important regulatory components of tight junction permeability. A better understanding of the involvement of claudin-2 in intestinal barrier functions requires the characterization of its distribution and regulation in the intestine. Interestingly, the claudin-2 gene promoter harbors a number of similarities to that of sucrase-isomaltase, a marker of enterocyte differentiation. We thus investigated the expression of claudin-2 in relation to the transcription factors CDX2, HNF-1alpha, and GATA-4 in the human intestine. The characterization of claudin-2 and the expression of the above transcription factors were performed by immunofluorescence, Western blot, and RT-PCR in the developing human intestinal epithelium. The functional role of CDX2, HNF-1alpha, and GATA-4 on claudin-2 regulation was also examined by ectopic expression studies in intestinal cell models. Claudin-2 was detected in both crypt and villus cells of the small intestine but restricted to undifferentiated crypt cells in the colon. CDX2 and HNF-1alpha were expressed along the entire intestine whereas GATA-4 was undetectable in the colon. Accordingly, in the colonic Caco-2 cell model, claudin-2 was found to be present only in undifferentiated cells. Like in the colonic epithelium, GATA-4 was found to be also lacking in Caco-2 cells while CDX2 and HNF-1alpha were present at significant levels. Cotransfection experiments showed that the claudin-2 promoter was activated by CDX2, HNF-1alpha, and GATA-4 in a cooperative manner. Furthermore, forced GATA-4 expression in Caco-2 cells enhances maintenance of claudin-2 expression during differentiation. These observations suggest that optimal claudin-2 expression in the gut relies on the presence of GATA-4, suggesting a role for this factor in intestinal regionalization.

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.

The Down regulated in Adenoma (dra) gene encodes an intestine-specific membrane sulfate transport protein

A gene has been described, Down Regulated in Adenoma (dra), which is expressed in normal colon but is absent in the majority of colon adenomas and adenocarcinomas. However, the function of this protein is unknown. Because of sequence similarity to a recently cloned membrane sulfate transporter in rat liver, the transport function of Dra was examined. We established that dra encodes for a Na(+)-independent transporter for both sulfate and oxalate using microinjected Xenopus oocytes as an assay system. Sulfate transport was sensitive to the anion exchange inhibitor DIDS (4,4'-diisothiocyano-2,2' disulfonic acid stilbene). Using an RNase protection assay, we found that dra mRNA expression is limited to the small intestine and colon in mouse, therefore identifying Dra as an intestine-specific sulfate transporter. dra also had a unique pattern of expression during intestinal development. Northern blot analysis revealed a low level of expression in colon at birth with a marked increase in the first 2 postnatal weeks. In contrast, there was a lower, constant level of expression in small intestine in the postnatal period. Caco-2 cells, a colon carcinoma cell line that differentiates over time in culture, demonstrated a marked induction of dra mRNA as cells progressed from the preconfluent (undifferentiated) to the postconfluent (differentiated) state. These results show that Dra is an intestine-specific Na(+)-independent sulfate transporter that has differential expression during colonic development. This functional characterization provides the foundation for investigation of the role of Dra in intestinal sulfate transport and in the malignant phenotype.

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.

Expression from the proximal promoter of the carbonic anhydrase 1 gene as a marker for differentiation in colon epithelia

Carbonic anhydrase 1 (CA1) catalyses the reversible hydration of CO2 and is important for cellular diffusion of CO2, ion transport and pH regulation. The gene encoding CA1 (CA1) has two promoters. In adult colon epithelia the proximal promoter determines high levels of expression and the distal erythroid promoter is repressed. RNA in situ hybridisation shows that CA1 mRNA is abundant in differentiating cells of the colonic crypt as they migrate to the luminal surface, but is not present at the base of the crypts and levels are low on the luminal surface. It is likely that CA1 gene expression in these cells is regulated by differential transcription and/or mRNA stability. In contrast CA1 protein is localised predominantly on the luminal surface. Since CA1 mRNA and protein do not exactly co-localise it can be inferred that CA1 expression is also subject to post-transcriptional control. CA1 mRNA is significantly reduced in colon carcinoma and in adenomas from familial adenomatous polyposis patients. Loss of CA1 expression is associated with the disappearance of differentiated epithelial cells. Out of twelve colon carcinoma cell lines three, LIM1215, LIM1899 and HT115, expressed CA1 and nine did not. This variation in expression may also be associated with cell type differentiation.

Intrinsic factor receptor during fetal development of the human intestine

Intrinsic factor receptor activity was observed in mucosal homogenates from whole small intestine and colon of 10-19-week fetuses, whereas it was only detected in the distal part of the small intestine of a 25-week fetus. The receptor-intrinsic factor-cobalamin complex was eluted into the void-volume position when ileum mucosal extract was assayed for receptor activity by gel filtration after incubation with either fetal gastric extract or human gastric juice. The intrinsic-factor-binding capacity of intestinal mucosal extracts ranged from 2.6 to 30.5 fmol/mg and was correlated with the gestational age of six fetuses. The dissociation constant of the receptor for the intrinsic factor-cobalamin complex was estimated at 0.24-0.36 nM at pH 7.4. In conclusion, intrinsic-factor-receptor activity was detected in the whole intestine in 10-19-week fetuses, whereas it was only present in the distal ileum at the end of fetal development.

Sucrase-isomaltase expression in chronic ulcerative colitis and dysplasia

Sucrase-isomaltase (SI) is a mucosal disaccharidase that is present in normal small intestine and fetal colon. It also has been noted in colonic adenomas and adenocarcinomas. We used a polyclonal antibody to human SI to investigate enzyme presence and utility in detecting dysplastic changes in chronic ulcerative colitis. Sections from 32 cases were reviewed for the presence or absence of active colitis and dysplasia. Immunostaining of these cases for SI was performed and the results were reported based on location of immunoreactivity (ie, membrane and cytoplasmic staining in superficial and crypt epithelial cells) and percentage of positivity. Of 81 sections examined, 48 were rated negative for dysplasia (23 inactive colitis, 20 active, and five probably negative) and 28 were rated positive (eight low grade and 20 high grade). Surface membrane staining of epithelial cells was noted in all 28 dysplastic slides and positive cases (sensitivity, 100%) but also in 29 of 48 negative sections (P less than .001). In contrast, cytoplasmic positivity was present in 25 of 28 dysplastic and in only two of 48 negative slides (P less than .0001). The presence of cytoplasmic staining of SI in the superficial or crypt cells revealed a sensitivity of 92% and a specificity of 94%. There were five additional sections rated as indefinite for dysplasia (probably positive or unknown); two showed staining patterns typical of negative slides and three showed positive staining patterns. Of the 18 samples of transitional mucosa next to areas of dysplasia, surface membrane staining of SI was seen in all samples and cytoplasmic staining was seen in 15. We conclude that membrane staining of SI can be detected in inflammatory, regenerative, and dysplastic mucosa in ulcerative colitis. Cytoplasmic staining, however, correlates strongly with the presence of dysplastic change and may help in its detection.

Clonal analysis of sucrase-isomaltase expression in the human colon adenocarcinoma Caco-2 cells

To investigate the biosynthetic basis for the mosaic expression of brush border enzymes in confluent Caco-2 cells, a human colon carcinoma cell line exhibiting characteristics of adult small intestinal enterocytes, we have obtained a series of clones differing markedly in their growth rates, amounts of transforming growth factor-alpha/epidermal growth factor-like activity released into the culture medium, and sucrase-isomaltase (SI) activity. Other intestinal markers (aminopeptidase N, dipeptidylpeptidase IV, lactase, alkaline phosphatase and 'crypt cell antigen') displayed a much more limited variability in expression, suggesting that the Caco-2 cell clones we have obtained did not differ in their overall ability to differentiate. Immunofluorescence staining, metabolic labelling with radioactive methionine and hybridization analysis of SI mRNA abundance were used to investigate SI synthesis and its regulation in clones endowed with low, intermediate or high sucrase activity. The results obtained have demonstrated heterogeneous SI expression, even in clonal cell lines, and a negative correlation between SI expression and growth factor concentrations in the culture medium, suggesting an autocrine regulation of cell proliferation and differentiation in confluent Caco-2 cells. Pulse-chase experiments using the two clones endowed with the lowest and highest levels of SI activity, followed by immunoprecipitation of labelled SI with epitope-specific antibodies and SDS/PAGE analysis, suggested that both transcriptional and post-translational mechanisms play a role in the regulation of SI expression in intestinal cells.

Expression of Na(+)-coupled sugar transport in HT-29 cells: modulation by glucose

The human colon carcinoma cell line HT-29 adapted to grow in absence of glucose exhibits a typical enterocytic differentiation. In contrast, cells grown in glucose always remain undifferentiated. To investigate whether differentiated HT-29 cells express a Na(+)-dependent sugar transporter, isotopic tracer flux measurements of a non-metabolizable sugar analogue methyl alpha-D-glucoside (AMG) were undertaken. AMG accumulation in confluent monolayer of differentiated HT-29 cells was inhibited by replacement of sodium, phlorizin, phloretin, and glucose. Kinetic studies demonstrate the presence of only one Na(+)-dependent phlorizin-sensitive sugar transporter in differentiated HT-29 cells. Undifferentiated HT-29 cells cultured in the presence of glucose did not show a Na(+)-dependent AMG accumulation. As previously demonstrated for other markers of the enterocytic differentiation, this transporter has a growth-related expression. Moreover, it shares similar properties with the Na(+)-dependent glucose transport in the human fetal small intestine and colon. To demonstrate that the expression of the Na(+)-dependent sugar cotransporter can be modulated by glucose, differentiated HT-29 cells grown in glucose-free medium were switched to 25 mM glucose. In that condition the Na(+)-dependent AMG uptake was almost abolished. However, when these cells were switched back to glucose-free medium, the Na(+)-dependent AMG uptake was restored, although at a lower level. These experiments show that differentiated HT-29 cells are a good cellular model to study the regulation of the Na(+)-dependent sugar transporter.

A morphological study of a human adenocarcinoma cell line (HT29) differentiating in culture. Similarities to intestinal embryonic development

HT29 cells, a human adenocarcinoma cell line, when grown in Dulbecco's modified Eagle's medium (DMEM), form a multilayer of morphologically undifferentiated and unpolarized cells. However, when DMEM is replaced by RPMI medium, after 1-4 passages, a large amount of intracellular (ICL) and intercellular (ITCL) or secondary lumina (SL) are observed. These are detected in the light microscope and appear in the electron microscope as spherical structures embedded inside a multilayer of cells and bordered with microvilli. After 4-15 passages in RPMI, the cells retain the same pattern of cell growth but in addition exhibit apical brush-border microvilli and reveal a well developed belt of tight junctions. After 15 passages a single layer of polarized cells is clearly observed and a large number of 'domes' appeared. These results show that each of these culture types mimics morphologically specific stages described during intestinal ontogenesis between the 9th and the 16th week in the human embryo.

Detection and characterization of sucrase-isomaltase in adult human colon and in colonic polyps

A panel of monoclonal antibodies specific for sucrase-isomaltase, but differing in their ability to stain the proliferative crypt cells in human jejunum, was used to investigate expression of this enzyme in adult human colon and colonic tumors. Immunofluorescence staining on cryostat sections demonstrated the presence of sucrase-isomaltase in the apical region of normal colonic crypt cells but not on surface epithelium. Colonic sucrase-isomaltase was purified by immunoprecipitation with selected monoclonal antibodies and identified predominantly as high-mannose and complex glycosylated single-chain precursors endowed with relatively low levels of enzyme activities. Most polyps examined (10/16) were also found to express significant amounts of sucrase-isomaltase. In contrast, only 3 of 45 adenocarcinomas were positive by immunofluorescence staining; no correlation was found between enzyme expression and tumor classification either by "Dukes" stage or degree of histological differentiation. These results demonstrate that colonic crypt cells and some benign tumor cells synthesize and express at their cell surface a form of sucrase-isomaltase immunologically distinct from that present in the brush borders of small intestinal villose cells.

Sucrase-isomaltase expression and enterocytic ultrastructure of human colorectal tumors

We report the relative frequency of sucrase-isomaltase (SI) antigen expression in human colonic adenocarcinoma (22/57), in peritumoral mucosa taken next to the tumor (31/41) or distant from it (29/42) as well as in 21/23 polyps. Our results are based on indirect immunofluorescence with a monoclonal antibody (MAb) specific for human intestinal SI. A regular and intense expression of SI occurred only in 6 tumor specimens. In the remaining 16 SI-positive tumor samples, labelling was heterogeneous, i.e., scattered over more or less extensive areas. A similar irregular staining pattern was also found in polyps and in peritumoral mucosa, irrespective of its distance from the tumor. Electron microscopic examination of 19 carcinomas mostly revealed altered brush-border membrane features, irrespective of histological SI staining pattern. Brush-border enzyme activities of sucrase, alkaline phosphatase and maltase showed no difference between tumor specimens and peritumoral mucosa, but aminopeptidase was depressed in the former. Sucrase activity was extremely low (mean values 1.1 to 1.8 mU/mg protein) and rose only exceptionally to 17.5 mU/mg prot.

Structural and enzymatic changes during colonic maturation in the fetal and suckling rat

To assess correlations between cellular differentiation and enzymatic maturation in the developing rat colon, tissue from fetal, suckling, weanling, and adult rats was analyzed by electron microscopy and assayed for lactase, alkaline phosphatase, and sodium-potassium-stimulated adenosine triphosphatase activities. The proximal and distal colon were analyzed independently at all ages. All three enzymes were detected in the fetal colon when the cells were highly undifferentiated. Postnatally, significant regional differences in cellular ultrastructure appeared, only some of which were directly paralleled by enzymatic changes. Each enzyme had a distinct region-specific developmental pattern. Lactase and sodium-potassium-stimulated adenosine triphosphatase were significantly enhanced at birth, decreasing to adult levels by 15 days postnatal. Regional differences were present, but the patterns were similar. These patterns did not parallel the increase in microvillar height and number and basolateral interdigitations of the surface columnar cells, the structural correlates of lactase, and sodium-potassium-stimulated adenosine triphosphatase, respectively. In contrast, developmental changes in alkaline phosphatase activity paralleled structural maturation, at least in part. The activity levels in the distal colon did not change significantly with age and few major structural changes were noted. In the proximal colon, activity increased markedly after birth, and after 10 days decreased rapidly to adult levels, a pattern that coincided with the transient appearance of villi and specialized cells with apical tubules and vesicles known to have alkaline phosphatase activity. The results show age- and region-related changes in cellular ultrastructure and enzymatic activities, only some of which appear to be directly correlated.

Brush border membrane sucrase-isomaltase, maltase-glucoamylase and trehalase in mammals. Comparative development, effects of glucocorticoids, molecular mechanisms, and phylogenetic implications

1. Trehalase, sucrase-isomaltase and maltase-glucoamylase are three integral glycoproteins of the brush border membranes of the enterocytes. On the basis of a comparative study on alpha-glycosidase activities (sucrase, isomaltase, maltase, glucoamylase and trehalase) associated to these glycoproteins during neonatal development, mammals could be basically divided into three groups. 2. In rodents and rabbit alpha-glycosidase activities are low or undetectable during the suckling period and increase to adult levels during the weaning period. In cat, dog and the primates examined, alpha-glycosidase activities are well or fully developed at birth. 3. In ruminants and pinnipedia alpha-glycosidases are low or absent throughout life. 4. During the suckling period of rat, mouse and rabbit, glucocorticoids trigger a premature and dramatic increase of all alpha-glycosidases. 5. On the contrary, alpha-glycosidases development during the weaning period appears to be independent of glucocorticoids. Neither hypophysectomy nor adrenalectomy prevent the development of alpha-glycosidases; only the rate of increase is reduced. 6. Transplantations of intestinal isografts either in adult or suckling animal, have shown that (1) no systemic factor inhibits the expression of alpha-glycosidase, (2) alpha-glycosidases induction is neither triggered by luminal alimentary substances, nor by hormones, (3) alpha-glycosidase development is controlled by an intrinsic ontogenic program. 7. The use of an antiglucocorticoid failed to inhibit the spontaneous development of alpha-glycosidase activities. 8. The increase of maltase and sucrase activities triggered by glucocorticoids is associated with an increase of the concentration of two glycoproteins in the microvillous membrane: sucrase-isomaltase and maltase-glucoamylase. 9. After administration of glucocorticoids the increase of maltase, sucrase and trehalase is strongly inhibited by actinomycin-D and the increase of sucrase activity is associated with a parallel increase of sucrase-isomaltase mRNA. Transcription is most likely the primary site of control of alpha-glycosidase biosynthesis. 10. In the crypt cells, alpha-glycosidases biosynthesis appears to be triggered by a receptor-mediated glucocorticoid interaction. 11. The enterocytes synthesize more alpha-glycosidase molecules as they travel to the tip of the villi. 12. The simultaneous, biosynthesis of sucrase-isomaltase and maltase-glucoamylase triggered by glucocorticoids, as well as their simultaneous normal development suggest that they may be subjected to related control mechanisms. 13. It is suggested that sucrase-isomaltase and maltase-glucoamylase might have arisen by several cycles of partial gene duplication of an ancestor gene coding for a single site maltase-isomaltase; subsequent mutation would have transformed isomaltase into sucrase or glucoamylase.

Feeding the premature and compromised infant: gastrointestinal considerations

We have presented the current concepts of gastrointestinal ontogeny--the various factors governing the ontogeny of the gastrointestinal tract and the interaction and intricate relationship between different determinants. It is only through a better understanding of the development of the gut and the various factors affecting it that pediatric gastroenterologists are able to design nutritional support strategies for managing very young and compromised neonates.

The biosynthesis of intestinal sucrase-isomaltase in human embryo is most likely controlled at the level of transcription

Although sucrase-isomaltase appears in the small intestine at quite different stages of development in man as compared with most mammals, we find that in human embryo also the appearance of sucrase-isomaltase mRNA closely parallels that of sucrase and isomaltase activities, as we have previously found to be the case in baby rabbits. Also, in the proximal-distal gradient of human embryonic intestine (proximal small intestine greater than distal small intestine greater than colon) the levels of these enzyme activities and those of the corresponding mRNA correlate closely. Finally, glucocorticosteroid treatment of a human colon carcinoma cell line (Caco-2) in vitro or of baby rabbits in vivo leads to a parallel increase of both sucrase and isomaltase activities and of sucrase-isomaltase mRNA. We conclude that in man also, in spite of the different timing in development, the biosynthesis of sucrase-isomaltase is most likely to be controlled at the level of transcription or perhaps of the mRNA stability.

Developmental pattern of calmodulin-binding proteins in rat jejunal epithelial cells

Calmodulin-binding proteins have been studied in presumptive rat jejunal epithelial cells and in purified rat brush borders during development. Incubation of nitrocellulose replicas with [125I] calmodulin revealed that, at immature stages (13-15 days of fetal life), only two calmodulin-binding bands were detectable with molecular masses of approximately 145,000 and 135,000 daltons. By fetal day 19, additional calmodulin-binding proteins of 240,000 and 110,000 daltons were observed. The 145,000- and 240,000-dalton calmodulin-binding bands contained polypeptides that were immunologically similar to caldesmon and to the alpha-subunit of the non-erythroid spectrin (fodrin) respectively. Antisera reactive with the 110K subunit of the microvillus 110K-calmodulin complex labelled a 135,000-dalton band which comigrated with one of the calmodulin-binding proteins. This 135,000-dalton immunoreactive polypeptide persisted until birth but was absent in brush borders isolated from adult intestine. In addition, the 110K antisera reacted with an approximately 110,000-dalton subunit by fetal day 19. At birth, numerous lower-molecular-mass 110K immunoreactive bands were also detectable. Immunocytochemical localization of the three calmodulin-binding proteins revealed that, at fetal day 14, caldesmon and fodrin displayed fluorescence lining the periphery of the epithelial cells, whereas staining with the 110K antisera was very weak. At fetal day 19, staining with the three antisera resulted in bright fluorescence localized in the apical part of the epithelial cells, in parallel to the differentiation of brush borders. At this stage, the apical staining of the calmodulin-binding proteins was similar to that of the adult.(ABSTRACT TRUNCATED AT 250 WORDS)

The posttranslational processing of sucrase-isomaltase in HT-29 cells is a function of their state of enterocytic differentiation

The biosynthesis of sucrase-isomaltase was compared in enterocyte-like differentiated (i.e., grown in the absence of glucose) and undifferentiated (i.e., grown in the presence of glucose) HT-29 cells. Unlike differentiated cells, in which the enzyme is easily detectable and active, undifferentiated cells display almost no enzyme activity and the protein cannot be detected by means of cell surface immunofluorescence or immunodetection in membrane-enriched fractions or cell homogenates. Pulse experiments with L-[35S]-methionine show that the enzyme is, however, synthesized in these undifferentiated cells. As compared with the corresponding molecular forms in differentiated cells, the high-mannose form of the enzyme in undifferentiated cells is similarly synthesized and has the same apparent Mr. However, its complex form is less labeled and has a lower apparent Mr. Pulse-chase experiments with L-[35S]methionine show that, although the enzyme is synthesized to the same extent in both situations, the high-mannose and complex forms are rapidly degraded in undifferentiated cells, with an apparent half-life of 6 h, in contrast to differentiated cells in which the enzyme is stable for at least 48 h. A comparison of the processing of the enzyme in both situations shows that the conversion of the high-mannose to the complex form is markedly decreased in undifferentiated cells. These results indicate that the absence of sucrase-isomaltase expression in undifferentiated cells is not the consequence of an absence of biosynthesis but rather the result of both an impaired glycosylation and a rapid degradation of the enzyme.

Isolation of a cDNA probe for a human jejunal brush-border hydrolase, sucrase-isomaltase, and assignment of the gene locus to chromosome 3

We report the nucleotide sequence and derived amino acid sequence of a cDNA clone encoding most of the N-terminal, isomaltase region of human sucrase-isomaltase (SI). A plasmid containing this cDNA, pS12, identifies a 6-kb mRNA found in human jejunum and the human colon carcinoma cell line Caco-2. This human SI cDNA shows extensive overall homology with recently published rabbit SI cDNA. Using pS12 to probe DNA from a panel of somatic cell hybrids, we have assigned the gene encoding human SI to chromosome 3.