Laurie Drozdowski

β-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.

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.

Adaptation following intestinal resection: mechanisms and signals

The intestine has an inherent ability to adapt morphologically and functionally in response to internal and external environmental changes. The functional adaptations encompass modifications of the brush border membrane fluidity and permeability, as well as up- or down-regulation of carrier-mediated transport. Intestinal adaptation improves the nutritional status following the loss of a major portion of the small intestine, following chronic ingestion of ethanol, following sublethal doses of abdominal irradiation, in diabetes, in pregnancy and lactation, with ageing, and with fasting and malnutrition. Following intestinal resection, morphological and functional changes occur depending upon the extent of the intestine removed, the site studied, and the lipid content of the diet. Therefore, intestinal adaptation has important implications in the survival potential and welfare of the host. An understanding of the mechanisms of, and signals for, intestinal adaptation in the experimental setting forms the basis for the use of management strategies in humans with the short-bowel syndrome.

The age-associated decline in the intestinal uptake of glucose is not accompanied by changes in the mRNA or protein abundance of SGLT1.

Studies performed using human and animal models offer conflicting results regarding the effect of age on nutrient absorption. The objectives of this study were to determine (1) the effects of aging on the in vitro uptake of glucose in rats; and (2) the molecular mechanisms of these age-associated changes. Male Fischer 344 rats aged 1, 9 and 24 months were fed a standard laboratory diet (PMI # 5001). The uptake of 14C-labelled D-glucose was determined in vitro using the intestinal sheet method. Northern blotting, Western blotting and immunohistochemistry were used to determine the effects of age on the BBM sodium-dependent glucose transporter, SGLT1, and the BLM Na+K(+)-ATPase. When expressed on the basis of intestinal weight, mucosal weight or surface area, there was a reduction in glucose uptake in the 24-month-old animals. SGLT1, GLUT2 and Na+K(+)-ATPase mRNA and protein abundance did not parallel the changes seen in glucose uptake. These results indicate that (1) age reduces in vitro intestinal glucose uptake in the rat; and (2) this age-associated decline in glucose uptake was not explained by alterations in SGLT1, GLUT2 or Na+K(+)-ATPase.

The locally acting glucocorticosteroid budesonide enhances intestinal sugar uptake following intestinal resection in rats

Background and aims: Locally and systemically acting corticosteroids alter the morphology and transport function of the intestine. This study was undertaken to assess the effect of budesonide, prednisone, and dexamethasone on sugar uptake. Methods: Adult male Sprague Dawley rats underwent transection or resection of 50% of the middle portion of the small intestine, and in vitro uptake of sugars was measured. Results: The 50% enterectomy did not alter jejunal or ileal uptake of glucose or fructose. Prednisone had no effect on the uptake of glucose or fructose in resected animals. In contrast, in resected rats budesonide increased by over 120% the value of the jejunal maximal transport rate for the uptake of glucose, and increased by over 150% ileal uptake of fructose. Protein abundance and mRNA expression of the sodium dependent glucose transporter in brush border membrane (SGLT1), sodium independent fructose transporter in the brush border membrane (GLUT5), sodium independent glucose and fructose transporter in the basolateral and brush border membranes (GLUT2), and Na+/K+ ATPase α1 and β1 did not explain the enhancing effect of budesonide on glucose or fructose uptake. Budesonide, prednisone, and dexamethasone reduced jejunal expression of the early response gene c-jun. In resected animals, expression of the mRNA of ornithine decarboxylase (ODC) in the jejunum was reduced, and corticosteroids reduced jejunal expression of the mRNA of proglucagon. Conclusions: These data suggest that the influence of corticosteroids on sugar uptake in resected animals may be achieved by post translational processes involving signalling with c-jun, ODC, and proglucagon, or other as yet unknown signals. It remains to be determined whether budesonide may be useful to stimulate the absorption of sugars following intestinal resection in humans.

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.

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.

Dietary Lipids Modify Intestinal Lipid-Binding Protein RNA Abundance in Diabetic and Control Rats

Background: Lipid-binding proteins have been identified in the enterocyte, including the cytosolic intestinal and liver fatty acid binding proteins (I-FABP and L-FABP, respectively) as well as the brush border membrane fatty acid transporter (FAT). It is unclear whether variations in the type of dietary lipids or diabetes modify the RNA abundance of these proteins. Diabetes is associated with an increased intestinal lipid uptake, and the lipid uptake is greater in rats fed a semisynthetic saturated fatty acid (SFA) as compared with a polyunsaturated fatty acid (PUFA) diet. Methods: Male Sprague-Dawley rats were injected with streptozotocin or control vehicle and fed chow or either SFA or PUFA for 2 weeks. Northern blotting was performed on RNA isolated from jejunal and ileal tissues. Results: In controls, feeding SFA as compared with PUFA reduced the jejunal abundance of I-FABP and L-FABP RNA. In diabetic rats, feeding SFA increased the ileal FAT RNA. Feeding PUFA reduced jejunal L-FABP and ileal FAT RNA in diabetic rats as compared with controls. Conclusions: The enhanced lipid uptakes reported with feeding an SFA diet or with diabetes were not associated with parallel alterations in lipid-binding proteins. We speculate that these lipid-binding proteins act as a storage mechanism for lipids in enterocytes and are not directly involved in lipid uptake.

REVIEW: Small Bowel Review: Normal Physiology, Part 1

In the past year there have been many advances in the area of small bowel physiology and pathology and therapy. In preparation for this review, over 1500 papers were assessed. The focus is on presenting clinically useful information for the practising gastroenterologist. Selected important clinical learning points include the following: (1) numerous peptides are being identified which stimulate the proliferation and functional response of the small intestine to disease or resection, and may in time find a clinical use; (2) under usual in vivo conditions, absorption of nutrients has little effect on the paracellular movement of water; (3) the permeability of the intestine is modified by the function of the tight junctions, and measuring intestinal permeability may be useful to reflect the presence of disease; (4) the release of serotonin is influenced by cholinergic, adrenergic, and nonadrenergic, noncholinergic mechanisms, and serotonin agonists and antagonists may play an important future role in the treatment of motility disorders; (5) the use of endothelin receptor antagonists may be useful for the treatment of intestinal anaphylaxis; (6) the alterations in intestinal pH and motility in patients with Crohns disease may influence the action of pH- or time-dependent release medications; and (7) patients with irritable bowel syndrome may also have abnormalities in gastric and small intestinal motility.

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 (l-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.