Dexamethasone and GLP-2 administered to rat dams during pregnancy and lactation have late effects on intestinal sugar transport in their postweaning offspring.

Intestinal function in young animals is influenced by maternal factors, such as alterations in the maternal diet. Glucagon-like peptide 2 (GLP-2) enhances intestinal growth and absorption in mature animals. Glucocorticosteroids induce intestinal maturation in neonates and increase sugar uptake in adult animals. It is not known if maternally administered GLP-2 or glucocorticosteroids have persistent effects on intestinal transport in the offspring. This study was undertaken to determine (1) the influence of maternal GLP-2, dexamethasone (DEX) and GLP-2+DEX on intestinal sugar uptake in postweaning offspring and (2) if alterations in uptake are due to variations in intestinal morphology, sugar transporter abundance or the abundance of selected signals. Nursing rat dams were treated during pregnancy and lactation with GLP-2 (0.1 mug/g per day sc), DEX (0.128 microg/g per day sc), GLP-2+DEX or placebo. The offspring were sacrificed 4 weeks after weaning, and glucose and fructose uptake was determined using an in vitro intestinal ring uptake technique. sodium-dependent glucose transporter, glucose transporter (GLUT) 5, GLUT2, sodium potassium adenosine triphosphatase and selected signals were assessed by immunohistochemistry. The treatments did not affect body weights or intestinal morphology. GLP-2 and GLP-2+DEX increased jejunal fructose uptake, and GLP-2+DEX increased the jejunal and ileal maximal transport rate for glucose uptake. Protein kinase B and mammalian target of rapamycin abundance were also increased, while transporter abundance was unchanged. We speculate that these alterations in sugar uptake may be due to changes in the intrinsic activity of the transporters mediated by the phosphatidylinositol-3-kinase pathway. These alterations in uptake may have nutritional implications for the offspring of mothers who may be treated with GLP-2 or glucocorticosteroids.

Dietary gangliosides enhance in vitro glucose uptake in weanling rats.

BACKGROUND: The intestine adapts to environmental stimuli, such as modifications in dietary lipids. Dietary lipids modify brush border membrane (BBM) permeability and nutrient transporter activities. Gangliosides (GANG) are glycolipids present in human milk, but they are present only in low amounts in infant formula. Exogenous GANG are incorporated into cell membranes and increase their permeability. This study was undertaken to determine if feeding a 0.2% GANG-enriched diet for 2 weeks alters in vitro intestinal sugar absorption in weanling rats compared with an isocaloric control diet or diet enriched with polyunsaturated long-chain fatty acids. METHODS: In vitro uptake of 34-96 mm glucose and fructose and morphological measurements were assessed on intestinal tissue of weanling rats. Western blotting, immunohistochemistry, Northern blotting, and reverse transcription-polymerase chain reaction were performed to determine the mRNA and protein abundance of the sugar transporters SGLT-1, GLUT2 and GLUT5. RESULTS: Feeding GANG did not alter the rates of animal weight gain or intestinal morphology. GANG did not affect fructose uptake. Depending on the concentration of glucose, GANG increased jejunal uptake of higher concentrations of glucose by approximately 20%-60%. There were no changes in GLUT5 or GLUT2 protein or mRNA abundance. Similarly, there were no changes in SGLT-1 mRNA and protein abundance, as determined by Northern and Western blotting. However, using immunohistochemistry, SGLT-1 was lower in GANG than in controls. CONCLUSIONS: The results of this study suggest that the enhanced uptake of glucose that results from feeding 0.2% GANG for 2 weeks to weanling rats may be regulated posttranslationally. Clearly any adjustment of the content of GANG in infant formula must be studied carefully.

Intestinal sugar transport.

Carbohydrates are an important component of the diet. The carbohydrates that we ingest range from simple monosaccharides (glucose, fructose and galactose) to disaccharides (lactose, sucrose) to complex polysaccharides. Most carbohydrates are digested by salivary and pancreatic amylases, and are further broken down into monosaccharides by enzymes in the brush border membrane (BBM) of enterocytes. For example, lactase-phloridzin hydrolase and sucrase-isomaltase are two disaccharidases involved in the hydrolysis of nutritionally important disaccharides. Once monosaccharides are presented to the BBM, mature enterocytes expressing nutrient transporters transport the sugars into the enterocytes. This paper reviews the early studies that contributed to the development of a working model of intestinal sugar transport, and details the recent advances made in understanding the process by which sugars are absorbed in the intestine.

Lipid malabsorption persists after weaning in rats whose dams were given GLP-2 and dexamethasone.

Glucagon-like peptide-2 (GLP-2) enhances intestinal growth and absorption in mature animals, and glucocorticosteroids (GC) increase the sugar and lipid uptake in adult animals. However, the role of GC and GLP-2 in the ontogeny of lipid absorption is unknown. We hypothesized that GLP-2 and the GC dexamethasone (DEX), when administrated to rat dams during pregnancy and lactation, would enhance lipid uptake in the offspring. Rat dams were treated in the last 10 d of pregnancy and during lactation with GLP-2 [0.1 microg/g/d subcutaneous (sc)], DEX (0.128 microg/g/d sc), GLP-2 + DEX, or a placebo. Sucklings were sacrificed at 19-21 d of age, and weanlings were sacrificed 4 wk later. Lipid uptake was assessed using an in vitro ring uptake method. Although DEX and GLP-2 + DEX increased the jejunal mass, the jejunal lipid uptake was unchanged. In contrast, GLP-2, DEX, and GLP-2 + DEX reduced the ileal lipid uptake in suckling and weanling rats. This reduction was not due to alterations in intestinal morphology or to changes in fatty acid-binding protein abundance, but it was partially explained by an increase in the effective resistance of the intestinal unstirred water layer. In sucklings, DEX dramatically reduced the jejunal lipid uptake to levels similar to those seen in weanlings, such that the normal ontogenic decline in lipid uptake was not observed. Giving dams GLP-2 or DEX during pregnancy and lactation reduced lipid uptake in the offspring, and this persisted for at least 1 mon. The impact this may have on the nutritional well-being of the animal in later life is unknown.

Age-associated changes in intestinal fructose uptake are not explained by alterations in the abundance of GLUT5 or GLUT2.

A reduction in nutrient absorption may contribute to malnourishment in the elderly. The objectives of this study were to determine the effects of aging on the absorption of fructose in rats, as well as the mechanisms of these adaptive changes. Male Fischer 344 rats aged 1, 9, and 24 months were fed standard Purina chow for 2 weeks (PMI #5001, PMI Nutritionals, Brentwood, MO). The uptake of (14)C-labeled D-fructose was determined in vitro using the intestinal sheet method. Intestinal samples were taken for RNA isolation and for brush border membrane (BBM) and basolateral membrane (BLM) preparation. Northern blotting, Western blotting, and immunohistochemistry were used to determine the effects of age and diet on GLUT5 and GLUT2. When expressed on the basis of intestinal or mucosal weights, aging was associated with a decline in jejunal and ileal fructose uptake, whereas jejunal fructose uptake was increased when expressed on the basis of serosal or mucosal surface area. The alterations in fructose uptake were not paralleled by changes in GLUT5 or GLUT2 abundance. These results indicate that 1) the effect of age on fructose uptake depends on the method used to express results, and 2) the age-associated changes in uptake are not explained by alterations in GLUT5 and GLUT2.

Short-chain fatty acids and total parenteral nutrition affect intestinal gene expression.

BACKGROUND: The supplementation of total parenteral nutrition (TPN) formulas with short-chain fatty acids (SCFAs) increases glucose uptake and the expression of glucose transporters in parenterally fed animals. Several signals may be involved in intestinal adaptation; however, increased messenger RNA (mRNA) levels for proglucagon and several early-response genes, including c-myc and c-fos, are seen in animals receiving SCFA-supplemented TPN. Although the effects of a mixture of SCFAs are well documented, the relative contribution of individual SCFAs is unknown. Butyrate is a preferred fuel of colonocytes, with documented effects on cellular proliferation and gene expression. Accordingly, this study was undertaken to determine the relative role of butyrate in initiating an adaptive response in nonresected rats receiving TPN. METHODS: Animals received standard TPN for 66 hours, followed by 6 hours of either standard TPN, TPN supplemented with a mixture of SCFAs (acetate, propionate, and butyrate, 60 mmol/L total), or TPN supplemented with butyrate alone (9 mmol/L). An oral control group was fed an elemental diet, similar in macronutrient content to the TPN, so that all animals received the same amount of energy daily. RESULTS: SCFAs increased ileal glucose transporter 2 (GLUT2) mRNA expression compared with the orally fed group. SCFAs also increased proglucagon mRNA expression compared with the TPN group. No changes in Na+K(+)-adenosine triphosphatase or early-response gene expression were found in this study. CONCLUSIONS: In a rat model of TPN, the use of 9 mmol/L butyrate did not have the same effect on GLUT2 and proglucagon expression as a 60-mmol/L mixture of SCFAs. This suggests that the effect of a mixture of SCFAs on intestinal gene expression is not butyrate specific.

The age-related decline in intestinal lipid uptake is associated with a reduced abundance of fatty acid-binding protein.

Aging is associated with changes in the absorptive capacity of the small intestine. We tested the hypotheses that (i) aging is associated with a decline in lipid absorption, and that (ii) this decreased lipid absorption is due to a decline in the abundance of mRNA and/or the enterocyte cytosolic intestinal FA-binding protein (I-FABP), the liver FA-binding protein (L-FABP), and the ileal lipid-binding protein (ILBP). In vitro uptake studies were performed on Fischer 344 rats at ages 1, 9, and 24 mon. Northern blotting (L-FABP, ILBP) and immunohistochemistry (I-FABP, ILBP) were performed. Aging was associated with decreased animal weights, but the surface area of the intestine was not significantly altered with age. The rates of ileal uptake of 16:0, 18:0, 18:1, and 18:2 were reduced by greater than 50% with aging when expressed on the basis of mucosal weight. This decline was not associated with reduced expression of mRNA for L-FABP or ILBP but was associated with a 50% decrease in the abundance of I-FABP and a 40% decrease in the abundance of ILBP. Thus, the decrease with aging in the ileal uptake of some FA when rates were expressed on the basis of mucosal weight was associated with a reduced abundance of I-FABP and ILBP.

An isocaloric PUFA diet enhances lipid uptake and weight gain in aging rats.

Aging is associated with a change in the morphology and absorptive capacity of the small intestine. In young rats, feeding a semisynthetic diet containing saturated FA (SFA) increases nutrient uptake, as compared with an isocaloric diet containing polyunsaturated FA (PUFA). We tested the hypotheses that (i) aging is associated with a decline in lipid absorption in the Fischer 344 rat; (ii) this decline can be corrected by manipulating the fat composition of the diet; and (iii) the age- and diet-associated variations in lipid uptake are associated with changes in the ileal lipid-binding protein (ILBP) or the intestinal or liver FA-binding proteins (I- or L-FABP, respectively) in the cytosol of the enterocyte. In rats fed SFA or PUFA, aging was associated with a decline in the in vitro uptake of stearic acid (18:0) when expressed on the basis of intestinal or mucosal weight. In contrast, age had no effect on lipid uptake when expressed on the basis of serosal surface area, whereas lipid uptake increased with age when expressed on the basis of mucosal surface area. The age-associated variations in lipid uptake were not associated with changes in protein abundance and/or expression of ILBP, I-FABP, or L-FABP. In 24-mon-old rats, when uptake of lipids was expressed on the basis of mucosal surface area, feeding PUFA enhanced lipid uptake and body weight gain as compared with rats fed SFA. Future studies must determine whether the enhanced lipid uptake and body weight gain observed in older animals fed PUFA have any therapeutic benefit.

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.

Beta-glucan extracts inhibit the in vitro intestinal uptake of long-chain fatty acids and cholesterol and down-regulate genes involved in lipogenesis and lipid transport in rats.

BACKGROUND: Dietary fiber reduces the intestinal absorption of nutrients and the blood concentrations of cholesterol and triglycerides. AIM: We wished to test the hypothesis that high-viscosity (HV) and low-viscosity preparations of barley and oat beta-glucan modify the expression of selected genes of lipid-binding proteins in the intestinal mucosa and reduce the intestinal in vitro uptake of lipids. METHODS: Five different beta-glucan extracts were separately added to test solutions at concentrations of 0.1-0.5% (wt/wt), and the in vitro intestinal uptake of lipids into the intestine of rats was assessed. An intestinal cell line was used to determine the effect of beta-glucan extracts on the expression of intestinal genes involved in lipid metabolism and fatty acid transport. RESULTS: All extracts reduced the uptake of 18:2 when the effective resistance of the unstirred water layer was high. When the unstirred layer resistance was low, the HV oat beta-glucan extract reduced jejunal 18:2 uptake, while most extracts reduced ileal 18:2 uptake. Ileal 18:0 uptake was reduced by the HV barley extract, while both jejunal and ileal cholesterol uptakes were reduced by the medium-purity HV barley extract. The inhibitory effect of HV barley beta-glucan on 18:0 and 18:2 uptake was more pronounced at higher fatty acid concentrations. The expression of genes involved in fatty acid synthesis and cholesterol metabolism was down-regulated with the HV beta-glucan extracts. beta-Glucan extracts also reduced intestinal fatty-acid-binding protein and fatty acid transport protein 4 mRNA. CONCLUSIONS: The reduced intestinal fatty acid uptake observed with beta-glucan is associated with inhibition of genes regulating intestinal uptake and synthesis of lipids. The inhibitory effect of beta-glucan on intestinal lipid uptake raises the possibility of their selective use to reduce their intestinal absorption.

Morphological, kinetic, membrane biochemical and genetic aspects of intestinal enteroplasticity.

The process of intestinal adaptation ("enteroplasticity") is complex and multifaceted. Although a number of trophic nutrients and non-nutritive factors have been identified in animal studies, successful, reproducible clinical trials in humans are awaited. Understanding mechanisms underlying this adaptive process may direct research toward strategies that maximize intestinal function and impart a true clinical benefit to patients with short bowel syndrome, or to persons in whom nutrient absorption needs to be maximized. In this review, we consider the morphological, kinetic and membrane biochemical aspects of enteroplasticity, focus on the importance of nutritional factors, provide an overview of the many hormones that may alter the adaptive process, and consider some of the possible molecular profiles. While most of the data is derived from rodent studies, wherever possible, the results of human studies of intestinal enteroplasticity are provided.

Maternal dexamethasone and GLP-2 have early effects on intestinal sugar transport in their suckling rat offspring.

Both glucagon-like peptide 2 (GLP-2) and glucocorticosteroids enhance intestinal uptake in mature animals. Maternal stimuli may cause intestinal adaptation in the offspring. We hypothesized that administering GLP-2, dexamethasone (DEX) or a combination of GLP-2+DEX to rat dams during pregnancy and lactation would enhance intestinal sugar uptake in their offspring. Rat dams were treated with GLP-2 (0.1 microg/g/day), DEX (0.128 microg/g/day), a combination of GLP-2+DEX or placebo. Glucose and fructose uptake was assessed in their suckling offspring using an in vitro intestinal ring uptake technique. The protein abundance of SGLT1, GLUT5, GLUT2, Na(+)K(+)-ATPase and selected signals was determined by immunohistochemistry; GLP-2 caused hypertrophy of the jejunal enterocytes and increased ileal villous height. Jejunal fructose uptake was reduced by GLP-2, DEX and GLP-2+DEX. V(max) for jejunal glucose uptake was reduced with DEX and GLP-2+DEX. These declines were not explained by alterations in transporter abundance. Decreases in Akt and mTOR abundance were associated with declines in transporter activity. We speculate that the intrinsic activity of the sugar transporters was modified via the P13K pathway. In conclusion, maternal GLP-2 and DEX reduced intestinal sugar uptake in their offspring. This may have nutritional implications for the offspring of mothers treated with GLP-2 or steroids.

A combination of dexamethasone and glucagon-like peptide-2 increase intestinal morphology and glucose uptake in suckling rats.

OBJECTIVES: Glucagon-like peptide (GLP)-2 enhances nutrient uptake in adult animals. Glucocorticosteroids accelerate intestinal ontogeny and increase nutrient uptake in adult animals. We hypothesized that administering GLP-2 and dexamethasone (DEX) to suckling rats will enhance sugar uptake and that this effect persists into the postweaning period. METHODS: Suckling rats were treated for 10 days with GLP-2 (0.1 microg/g/d, twice daily), DEX (0.128 microg/g/d, once daily), GLP-2 + Dex (same doses as above), or placebo. The rate of intestinal uptake of glucose and fructose in sucklings (19-21 days old) and weanlings (49 days old) was assessed using an in vitro ring technique. RESULTS: DEX reduced body weight in weanlings, whereas GLP-2 + DEX prevented this effect. In sucklings, GLP-2 + DEX increased ileal villous height and jejunal and ileal villous width and crypt depth. In sucklings, GLP-2 + DEX increased the maximal transport rate (Vmax) for jejunal glucose uptake, whereas DEX reduced the ileal Vmax. In weanlings, GLP-2 + DEX increased jejunal villous height, whereas ileal villous width and crypt depth were reduced. DEX increased the ileal Vmax and apparent affinity constant for glucose in weanlings. CONCLUSIONS: The combination of these hormones may be useful in stimulating glucose uptake in the developing intestine, and giving DEX to sucklings may enhance glucose uptake in later life.

Dietary gangliosides enhance in vitro lipid uptake in weanling rats.

BACKGROUND: The intestine adapts morphologically or functionally in response to environmental stimuli. Dietary lipids modify brush border membrane (BBM) permeability and nutrient transporter activities. Gangliosides (GANG) are glycolipids in human milk that are present only in low amounts in infant formula. Exogenous GANG are incorporated into cell membranes and increase their permeability. The objective of this study was to determine whether feeding a GANG-enriched diet alters in vitro intestinal lipid absorption. METHODS: Weanling rats were fed either (1) GANG-enriched diet; (2) diet enriched with polyunsaturated long-chain fatty acids; or (3) isocaloric control diet for 2 weeks, after which in vitro intestinal lipid uptake was measured. RESULTS: Feeding GANG did not alter weight gain or intestinal morphology. Enhanced uptake of stearic acid (18:0) in the ileum and stearic and linoleic acid (18:2) in the jejunum was not associated with a change in the abundance of the ileal lipid binding protein (ILBP), the intestinal fatty acid binding protein (I-FABP), or the liver fatty acid binding protein (L-FABP). CONCLUSION: We speculate that the enhanced uptake of long-chain fatty acids in weanling rats fed GANG may be caused by a modification in physical properties of the BBM.