Small Intestinal Enterocytes Research Articles

Enzymes involved in l-carnitine biosynthesis are expressed by small intestinal enterocytes in mice: Implications for gut health

BackgroundCarnitine is essential for mitochondrial β-oxidation of long-chain fatty acids. Deficiency of carnitine leads to severe gut atrophy, ulceration and inflammation in animal models of carnitine deficiency. Genetic studies in large populations have linked mutations in the carnitine transporters OCTN1 and OCTN2 with Crohn's disease (CD), while other studies at the same time have failed to show a similar association and report normal serum carnitine levels in CD patients. MethodsIn this report, we have studied the expression of carnitine-synthesizing enzymes in intestinal epithelial cells to determine the capability of these cells to synthesize carnitine de novo. We studied expression of five enzymes involved in carnitine biosynthesis, namely 6-N-trimethyllysine dioxygenase (TMLD), 4-trimethylaminobutyraldehyde dehydrogenase (TMABADH), serine hydroxymethyltransferase 1 and 2 (SHMT1 and 2) and γ-butyrobetaine hydroxylase (BBH) by real-time PCR in mice (C3H strain). We also measured activity of γ-BBH in the intestine using an ex vivo assay and localized its expression by in situ hybridization. ResultsOur investigations show that mouse intestinal epithelium expresses all five enzymes required for de novo carnitine biosynthesis; the expression is localized mainly in villous surface epithelial cells throughout the intestine. The final rate-limiting enzyme γ-BBH is highly active in the small intestine; its activity was 9.7±3.5pmol/mg/min, compared to 22.7±7.3pmol/mg/min in the liver. ConclusionsWe conclude that mouse gut epithelium is able to synthesize carnitine de novo. This capacity to synthesize carnitine in the intestine may play an important role in gut health and can help explain lack of clinical carnitine deficiency signs in subjects with mutations with OCTN transporters.

Cinnamon polyphenols regulate multiple metabolic pathways involved in insulin signaling and intestinal lipoprotein metabolism of small intestinal enterocytes

ObjectiveIncreasing evidence suggests that dietary factors may affect the expression of multiple genes and signaling pathways, which regulate intestinal lipoprotein metabolism. The small intestine is actively involved in the regulation of dietary lipid absorption, intracellular transport, and metabolism and is closely linked to systemic lipid metabolism. Cinnamon polyphenols have been shown to improve glucose, insulin, and lipid metabolism and improve inflammation in cell culture, animal, and human studies. However, little is known of the effects of an aqueous cinnamon extract (CE) on the regulation of genes and signaling pathways related to intestinal metabolism. The aim of the study was to investigate the effects of a CE on the primary enterocytes of chow-fed rats. MethodsFreshly isolated intestinal enterocytes were used to investigate apolipoprotein-B48 secretion by immunoprecipitation; gene expressions by quantitative reverse transcriptase-polymerase chain reaction and the protein and phosphorylation levels were evaluated by western blot and flow cytometric analyses. ResultsEx vivo, the CE significantly decreased the amount of apolipoprotein-B48 secretion into the media, inhibited the mRNA expression of genes of the inflammatory cytokines, interleukin-1β, interleukin-6, and tumor necrosis factor-α, and induced the expression of the anti-inflammatory gene, Zfp36. CE also increased the mRNA expression of genes leading to increased insulin sensitivity, including Ir, Irs1, Irs2, Pi3k, and Akt1, and decreased Pten expression. CE also inhibited genes associated with increased cholesterol, triacylglycerols, and apolipoprotein-B48 levels, including Abcg5, Npc1l1, Cd36, Mttp, and Srebp1c, and facilitated Abca1 expression. CE also stimulated the phospho-p38 mitogen-activated protein kinase, c-Jun N-terminal kinase, and extracellular-signal-regulated kinase expressions determined by flow cytometry, with no changes in protein levels. ConclusionsThese results demonstrate that the CE regulates genes associated with insulin sensitivity, inflammation, and cholesterol/lipogenesis metabolism and the activity of the mitogen-activated protein kinase signal pathway in intestinal lipoprotein metabolism.

PCSK9 siRNA suppresses the inflammatory response induced by oxLDL through inhibition of NF-κB activation in THP-1-derived macrophages

Proprotein convertase subtilisin/kexin 9 (PCSK9), a member of the protein-converting enzyme family, is highly expressed in adult hepatocytes and small intestinal enterocytes. To our knowledge, in this study, we demonstrate for the first time that PCSK9 is upregulated in a dose-dependent manner via oxidized low-density lipoprotein (oxLDL) stimulation in THP-1-derived macrophages. PCSK9 small interfering RNA (siRNA) suppresses the oxLDL-induced inflammatory cytokine expression in THP-1-derived macrophages. The exposure of macrophages to oxLDL markedly increased the expression of NF-κB protein in the nucleus. However, this effect was significantly attenuated by PCSK9 siRNA. These findings indicate that PCSK9 expression is induced by oxLDL, and that PCSK9 siRNA protects against inflammation via the inhibition of NF-κB activation in oxLDL-stimulated THP-1-derived macrophages. Our results suggest that PCSK9 may be used as a therapeutic target for the treatment of atherosclerosis since PCSK9 siRNA suppresses oxLDL-induced IκB-α degradation and NF-κB nuclear translocation into THP-1-derived macrophages.

Intestinal incretin responses to increased GLUT2 expression – Chacun à son goût

Intestinal incretin responses to increased GLUT2 expression – Chacun à son goût

Myosin Ia is Required for CFTR Brush Border Membrane Trafficking and Ion Transport in the Mouse Small Intestine

In enterocytes of the small intestine, endocytic trafficking of CFTR channels from the brush border membrane (BBM) to the subapical endosomes requires the minus-end motor, myosin VI (Myo6). The subapical localization of Myo6 is dependent on myosin Ia (Myo1a) the major plus-end motor associated with the BBM, suggestive of functional synergy between these two motors. In villus enterocytes of the Myo1a KO mouse small intestine, CFTR accumulated in syntaxin-3 positive subapical endosomes, redistributed to the basolateral domain and was absent from the BBM. In colon, where villi are absent and Myo1a expression is low, CFTR exhibited normal localization to the BBM in the Myo1a KO similar to WT. cAMP-stimulated CFTR anion transport in the small intestine was reduced by 58% in the KO, while anion transport in the colon was comparable to WT. Co-immunoprecipitation confirmed the association of CFTR with Myo1a. These data indicate that Myo1a is an important regulator of CFTR traffic and anion transport in the BBM of villus enterocytes and suggest that Myo1a may power apical CFTR movement into the BBM from subapical endosomes. Alternatively, it may anchor CFTR channels in the BBM of villus enterocytes as was proposed for Myo1a's role in BBM localization of sucrase-isomaltase.

Cinnamon polyphenols regulate high‐fructose feeding and age‐induced decreases in sirtuins in rat intestinal enterocytes

Sirtuins (SIRTs) may play a role in aging, insulin sensitivity, lipid metabolism, stress responses, and inflammation. Cinnamon type A polyphenols (CPA) have also been shown to improve glucose, insulin, and lipid metabolism, and inflammation. However, little is known of the effects of CPA on the expression of SIRTs. In this study, Wistar rats were fed a fructose‐rich diet for 6 weeks to induce insulin resistance and freshly isolated intestinal enterocytes were used to investigate the effects of purified CPA in vitro on SIRTs genes by RT‐PCR and proteins by Western blot analyses. SIRT1, 2, 3, 5, and 7 gene expressions were increased by 20 and 100 μg/mL CPA after 2 and 4h treatment; SIRT1‐3 protein levels were higher in 100 μg/mL CPA‐treated enterocytes after 4h. Similar effects were observed in the small intestinal enterocytes isolated from older Wistar rats (65 wks) consuming a stock diet. These results suggest that cinnamon polyphenols may activate sirtuins in intestinal enterocytes functionally altered by diet and age (Funded by USDA CRADA No.58‐3K95‐7‐1184 with Integrity).

Carrier-mediated γ-aminobutyric acid transport across the basolateral membrane of human intestinal Caco-2 cell monolayers

The aim of the present study was to investigate the transport of γ-aminobutyric acid (GABA) across the basolateral membrane of intestinal cells. The proton-coupled amino acid transporter, hPAT1, mediates the influx of GABA and GABA mimetic drug substances such as vigabatrin and gaboxadol and the anticancer prodrug δ-aminolevulinic acid across the apical membrane of small intestinal enterocytes. Little is however known about the basolateral transport of these substances. We investigated basolateral transport of GABA in mature Caco-2 cell monolayers using isotope studies. Here we report that, at least two transporters seem to be involved in the basolateral transport of GABA. The basolateral uptake consisted of a high-affinity system with a Km of 290μM and Vmax of 75pmolcm−2min−1 and a low affinity system with a Km of approximately 64mM and Vmax of 1.6nmolcm−2min−1. The high-affinity transporter is Na+ and Cl− dependent. The substrate specificity of the high-affinity transporter was further studied and Gly-Sar, Leucine, gaboxadol, sarcosine, lysine, betaine, 5-hydroxythryptophan, proline and glycine reduced the GABA uptake to approximately 44–70% of the GABA uptake in the absence of inhibitor. Other substances such as β-alanine, GABA, 5-aminovaleric acid, taurine and δ-aminolevulinic acid reduced the basolateral GABA uptake to 6–25% of the uptake in the absence of inhibitor. Our results indicate that the distance between the charged amino- and acid-groups is particular important for inhibition of basolateral GABA uptake. Thus, there seems to be a partial substrate overlap between the basolateral GABA transporter and hPAT1, which may prove important for understanding drug interactions at the level of intestinal transport.

Absorption and Metabolism of cis‐9,trans‐11‐CLA and of Its Oxidation Product 9,11‐Furan Fatty Acid by Caco‐2 Cells

Furan fatty acids (furan-FA) can be formed by auto-oxidation of conjugated linoleic acids (CLA) and may therefore be ingested when CLA-containing foodstuff is consumed. Due to the presence of a furan ring structure, furan-FA may have toxic properties, however, these substances are toxicologically not well characterized so far. Here we show that 9,11-furan-FA, the oxidation product of the major CLA isomer cis-9,trans-11-CLA (c9,t11-CLA), is not toxic to human intestinal Caco-2 cells up to a level of 100 μM. Oil-Red-O staining indicated that 9,11-furan-FA as well as c9,t11-CLA and linoleic acid are taken up by the cells and stored in the form of triglycerides in lipid droplets. Chemical analysis of total cellular lipids revealed that 9,11-furan-FA is partially elongated probably by the enzymatic activity of cellular fatty acid elongases whereas c9,t11-CLA is partially converted to other isomers such as c9,c11-CLA or t9,t11-CLA. In the case of 9,11-furan-FA, there is no indication for any modification or activation of the furan ring system. From these results, we conclude that 9,11-furan-FA has no properties of toxicological relevance at least for Caco-2 cells which serve as a model for enterocytes of the human small intestine.

Rotavirus Infection in India: A Major Cause of Childhood Gastroenteritis

Rotaviruses are genetically highly variable, non-enveloped viruses with a double-stranded, segmented ribonucleic acid genome. It is the single most important cause of severe, dehydrating gastroenteritis in infants and young children worldwide. Rotavirus gastroenteritis is associated with high morbidity in developed countries and significant mortality in developing countries. In children aged less than 5 years, they are the most frequent agent of severe acute diarrheal illnesses. Typically, symptomatic rotavirus diseases in infants ( 70 years) arise with sudden onset of watery diarrhoea with high risk of dehydration, accompanied by vomiting. Fecal-oral transmission is the most likely route of virus spread. Group A serotype strains G1 through G4 account for more than 90% of rotavirus gastroenteritis in humans, with G1 being the predominant serotype. The virus preferentially infects the mature small-intestinal enterocytes. Treatment of rotavirus diarrhoea is usually symptomatic and comprises a sufficient fluid and electrolyte substitution. Although nitazoxanide and some other drugs show high efficacy against rotavirus in vitro and in vivo, there is currently no recommended specific antiviral therapy. In India, two efficient and secure live vaccines against rotaviruses have been approved. Rotarix (GSK) vaccine is derived from single attenuated human rotavirus G1P[8], whereas RotaTeq (Merck) is a pentavalent mixture of naturally attenuated bovine/human rotavirus reassortants. Though these vaccines have already dramatically decreased the morbidity associated with rotavirus in countries where they are widely used, the third generation of vaccines, based on inactivated viruses or recombinant virus like particles are already in pipeline. For prophylaxis, special attention should be paid to adequate hygienic rules. Because of the high stability of rotaviruses to changing environmental conditions, disinfection should be performed applying disinfectants with proven activity against rotaviruses.

A protocol for differentiation of human intestinal Caco-2 cells in asymmetric serum-containing medium

The human intestinal Caco-2 cell line still represents the best available in vitro model of absorptive enterocytes, despite its origin from a colon adenocarcinoma. Caco-2 cells seeded on filter inserts undergo in culture a process of spontaneous differentiation that leads to the formation, after two to three weeks, of a monolayer of polarized cell, coupled by tight junctions and expressing several morphological and functional features of small intestinal enterocytes. The medium normally used for differentiation of Caco-2 cells contains a supplement of foetal bovine serum (FBS) in both the apical (AP) and basolateral (BL) compartments. The use of FBS as cell culture media supplement has been frequently and increasingly questioned on scientific and also on ethical grounds. We have shown that addition of serum only to the BL medium (asymmetric protocol) appears to be sufficient to allow differentiation of Caco-2 cells, as monitored by morphology, monolayer permeability and alkaline phosphatase activity, compared to standard conditions using 10% FBS supplement in both AP and BL media (asymmetric protocol). Although not eliminating the use of FBS, its addition only in the BL medium results in more physiological conditions for differentiation and in a significant reduction of its use.

Phyto-phospholipid complex of catechin in value added herbal drug delivery

Catechin (an anti-inflammatory, antioxidant, antitumour, and hepatoprotective bioflavonoid) is poorly absorbed across the GIT because it has multiple ring molecules that are too large to be absorbed by simple diffusion. It typically has poor miscibility with oils and other lipids which limit their ability to pass across the lipid rich outer membranes of enterocytes of small intestine. Thus catechin–phospholipid complex were prepared to improve its absorption by imparting an environment of improved lipophilicity. The phospholipid complexes of catechin were prepared with phosphatidylcholine in presence of dichloromethane by conventional solvent evaporation technique. Pharmacosomes thus prepared were evaluated for solubility, drug content, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X ray powder diffraction (XRPD), in vitro dissolution study and in vitro antioxidant activity. Prepared phospholipid complex showed high drug content (99.40%. w/w) and improved lipid solubility (0.79–1.97 mg/mL). FTIR, NMR, DSC and XRPD data confirmed the formation of phospholipid complex. Unlike the free catechin, catechin complex showed a sustained release over the 24 h of study. Catechin-phospholipid complex showed slightly better antioxidant activity than that of catechin at all dose levels. Thus it can be concluded that the phospholipid complex of catechin may be of potential use for improving absorption of catechin across the lipidic biological barriers in gastrointestinal tract. It was concluded that the complexation with phospholipids did not interfere with the biological activities. This herbal drug delivery system can pave the way for large molecules to pass through the lipophilic biological membrane (by the virtue of their amphiphilic nature) and get absorbed into the systemic circulation.

Lipid raft-dependent adhesion of Giardia intestinalis trophozoites to a cultured human enterocyte-like Caco-2/TC7 cell monolayer leads to cytoskeleton-dependent functional injuries

Gardia intestinalis, the aetiological agent of giardiasis, one of the most common intestinal diseases in both developing and developed countries, induces a loss of epithelial barrier function and functional injuries of the enterocyte by mechanisms that remain unknown. Three possible mechanisms have been proposed: (i) Giardia may directly alter the epithelial barrier after a close interaction between the trophozoite and polarized intestinal cells, (ii) intestinal functions may be altered by factors secreted by Giardia including an 'enterotoxin', proteinases and lectins, and (iii) based on mouse studies, a mechanism involving the intervention of activated T lymphocytes. We used fully differentiated cultured human intestinal Caco-2/TC7 cells forming a monolayer and expressing several polarized functions of enterocytes of small intestine to investigate the mechanisms by which G. intestinalis induces structural and functional alterations in the host intestinal epithelium. We first report that adhesion of G. intestinalis at the brush border of enterocyte-like cells involves the lipid raft membrane microdomains of the trophozoite. We report an adhesion-dependent disorganization of the apical F-actin cytoskeleton that, in turn, results in a dramatic loss of distribution of functional brush border-associated proteins, including sucrase-isomaltase (SI), dipeptidylpeptidase IV (DPP IV) and fructose transporter, GLUT5, and a decrease in sucrose enzyme activity in G. intestinalis-infected enterocyte-like cells. We observed that the G. intestinalis trophozoite promotes an adhesion-dependent decrease in transepithelial electrical resistance (TER) accompanied by a rearrangement of functional tight junction (TJ)-associated occludin, and delocalization of claudin-1. Finally, we found that whereas the occludin rearrangement induced by G. intestinalis was related to apical F-actin disorganization, the delocalization of claudin-1 was not.

Analysis of proteomic changes induced upon cellular differentiation of the human intestinal cell line Caco‐2

The human intestinal cell line Caco-2 is a well-established model system to study cellular differentiation of human enterocytes of intestinal origin, because these cells have the capability to differentiate spontaneously into polarized cells with morphological and biochemical features of small intestinal enterocytes. Therefore, the cells are widely used as an in vitro model for the human intestinal barrier. In this study, a proteomic approach was used to identify the molecular marker of intestinal cellular differentiation. The proteome of proliferating Caco-2 cells was compared with that of fully differentiated cells. Two-dimensional gel analysis yielded 53 proteins that were differently regulated during the differentiation process. Pathway analysis conducted with those 34 proteins that were identified by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) analysis revealed subsets of proteins with common molecular and cellular function. It was shown that proteins involved in xenobiotic and drug metabolism as well as in lipid metabolism were upregulated upon cellular differentiation. In parallel, proteins associated with proliferation, cell growth and cancer were downregulated, reflecting the loss of the tumorigenic phenotype of the cells. Thus, the proteomic approach in combination with a literature-based pathway analysis yielded valuable information about the differentiation process of Caco-2 cells on the molecular level that contributes to the understanding of the development of colon cancer or inflammatory diseases such as ulcerative colitis--diseases associated with an imbalanced differentiation process of intestinal cells.

Development of high-throughput HILIC-MS/MS methodology for plasma citrulline determination in multiple species

Circulating citrulline originates almost exclusively from the small intestinal enterocytes in mammals and therefore is a potential biomarker of disease states affecting enterocyte mass including exposure to ionizing radiation. There is a need for a simple and rapid method for citrulline quantification in plasma. To achieve this goal, a high-throughput separation and tandem mass spectrometric detection strategy has been developed and validated in six different species. HILIC separation was achieved on a 1.7 μm fused-core Diol column using an acidic acetonitrile/water gradient. A surrogate analyte (citrulline stable isotope) was used to determine the lower-limit-of-quantitation, extraction recovery, and matrix ion effects. Mass spectrometric detection was achieved in the multiple reaction-monitoring mode using m/z 176 → 159, 177 → 160, and 181 → 164, for citrulline, citrulline+1, and citrulline+5, respectively. The retention time of citrulline and total chromatographic run time were 1.1 min and 2.5 min, respectively, while effectively eliminating matrix-ion effects and achieving baseline separation from the confounding amino acid arginine. Quantitation was precise (CV <4.3%), accurate (90–110%), and sensitive (lower-limit-of-quantitation; 0.125 μM) without interference from the confounding amino acid, arginine. The throughput of the method was enhanced by incorporation of a 96-well filter plate for final sample cleanup. The method was used to determine plasma citrulline in six different species and in mice treated with escalating doses of radiation. This simple, accurate and high-throughput (up to 200 samples/day) methodology provides the first quantitative assay to meet the growing demand for a rapid and simple citrulline assay with high sensitivity.

Functional roles of aspartate residues of the proton-coupled folate transporter (PCFT-SLC46A1); a D156Y mutation causing hereditary folate malabsorption

AbstractThe proton-coupled folate transporter (PCFT; SLC46A1) mediates folate transport into enterocytes in the proximal small intestine; pcft loss-of-function mutations are the basis for hereditary folate malabsorption. The current study explored the roles of Asp residues in PCFT function. A novel, homozygous, loss-of-function mutation, D156Y, was identified in a child of Pakistani origin with hereditary folate malabsorption. Of the 6 other conserved Asp residues, only one, D109, is shown to be required for function. D156Y, along with a variety of other substitutions at this site (Trp, Phe, Val, Asn, or Lys), lacked function due to instability of the PCFT protein. Substantial function was preserved with Glu, Gly, and, to a lesser extent, with Ser, Thr, and Ala substitutions. This correlated with PCFT bio-tinylated at the cell surface. In contrast, all D109 mutants, including D109E, lacked function irrespective of pH (4.5, 5.5, and 7.4) or substrate concentration (0.5-100μM), despite surface expression comparable to wild-type PCFT. Hence, D156 plays a critical role in PCFT protein stability, and D109, located in the first intracellular loop between the second and third transmembrane domains, is absolutely required for PCFT function.

Small Intestinal Alterations in Severely Obese Hyperglycemic Subjects

Type 2 diabetes mellitus (DM2) is associated with small intestinal hyperplasia and hypertrophy in rodents. Moreover, the small intestine is increasingly acknowledged to play a role in the pathophysiology of DM2. The objective of the study was to investigate the relation between plasma markers of small intestinal function and chronic hyperglycemia in man. We conducted a cross-sectional observational study of 40 severely obese subjects with chronic hyperglycemia and 30 severely obese subjects without chronic hyperglycemia who were indicated for bariatric surgery. We assessed plasma levels of citrulline, representing small intestinal enterocyte mass, intestinal fatty acid binding protein (I-FABP), a marker of enterocyte loss, and glucagon-like peptide-2, an intestinotrophic factor, and related them to glycated hemoglobin (HbA(1c)) levels. Plasma citrulline and I-FABP levels were both significantly elevated in subjects with chronic hyperglycemia (HbA(1c) > 6.0%) compared with subjects with a normal HbA(1c) (≤ 6.0%) (citrulline, 35 ± 2.1 μm vs. 26 ± 1.4 μm, P = 0.001; I-FABP, 140 ± 22 pg/ml vs. 69 ± 14 pg/ml, P = 0.001). Moreover, plasma citrulline and I-FABP levels correlated with HbA(1c) levels (citrulline, r(s) = 0.30, P = 0.02; I-FABP, r(s) = 0.33, P = 0.005). The I-FABP to citrulline ratio was higher in subjects with an elevated HbA(1c) (4.0 vs. 3.1, P = 0.03). Plasma glucagon-like peptide-2 levels were not related to citrulline or I-FABP levels (r(s) = 0.06, P = 0.67; r(s) 0.08, P = 0.54, respectively). Chronically elevated glucose levels in obese individuals are associated with increased small intestinal enterocyte mass and increased enterocyte loss. These findings argue for the further exploration of the role of the intestine in the pathophysiology of DM2.

Physiological relevance of cell-specific distribution patterns of CFTR, NKCC1, NBCe1, and NHE3 along the crypt-villus axis in the intestine.

We examined the cell-specific subcellular expression patterns for sodium- and potassium-coupled chloride (NaK2Cl) cotransporter 1 (NKCC1), Na(+) bicarbonate cotransporter (NBCe1), cystic fibrosis transmembrane conductance regulator (CFTR), and Na(+)/H(+) exchanger 3 (NHE3) to understand the functional plasticity and synchronization of ion transport functions along the crypt-villus axis and its relevance to intestinal disease. In the unstimulated intestine, all small intestinal villus enterocytes coexpressed apical CFTR and NHE3, basolateral NBCe1, and mostly intracellular NKCC1. All (crypt and villus) goblet cells strongly expressed basolateral NKCC1 (at approximately three-fold higher levels than villus enterocytes), but no CFTR, NBCe1, or NHE3. Lower crypt cells coexpressed apical CFTR and basolateral NKCC1, but no NHE3 or NBCe1 (except NBCe1-expressing proximal colonic crypts). CFTR, NBCe1, and NKCC1 colocalized with markers of early and recycling endosomes, implicating endocytic recycling in cell-specific anion transport. Brunner's glands of the proximal duodenum coexpressed high levels of apical/subapical CFTR and basolateral NKCC1, but very low levels of NBCe1, consistent with secretion of Cl(-)-enriched fluid into the crypt. The cholinergic agonist carbachol rapidly (within 10 min) reduced cell volume along the entire crypt/villus axis and promoted NHE3 internalization into early endosomes. In contrast, carbachol induced membrane recruitment of NKCC1 and CFTR in all crypt and villus enterocytes, NKCC1 in all goblet cells, and NBCe1 in all villus enterocytes. These observations support regulated vesicle traffic in Cl(-) secretion by goblet cells and Cl(-) and HCO(3)(-) secretion by villus enterocytes during the transient phase of cholinergic stimulation. Overall, the carbachol-induced membrane trafficking profile of the four ion transporters supports functional plasticity of the small intestinal villus epithelium that enables it to conduct both absorptive and secretory functions.

Escherichia coliK88ac Fimbriae Expressing Heat-Labile and Heat-Stable (STa) Toxin Epitopes Elicit Antibodies That Neutralize Cholera Toxin and STa Toxin and Inhibit Adherence of K88ac FimbrialE. coli

Enterotoxigenic Escherichia coli (ETEC) strains are a major cause of diarrheal disease in humans and animals. Bacterial adhesins and heat-labile (LT) and heat-stable (ST) enterotoxins are the virulence determinants in ETEC diarrhea. It is believed that vaccines inducing anti-adhesin immunity to inhibit bacterial adherence and anti-toxin immunity to eliminate toxin activity would provide broad-spectrum protection against ETEC. In this study, an ETEC fimbrial adhesin was used as a platform to express LT and STa for adhesin-toxin fusion antigens to induce anti-toxin and anti-adhesin immunity. An epitope from the B subunit of LT toxin (LTP1, (8)LCSEYRNTQIYTIN(21)) and an STa toxoid epitope ((5)CCELCCNPQCAGCY(18)) were embedded in the FaeG major subunit of E. coli K88ac fimbriae. Constructed K88ac-toxin chimeric fimbriae were harvested and used for rabbit immunization. Immunized rabbits developed anti-K88ac, anti-LT, and anti-STa antibodies. Moreover, induced antibodies not only inhibited adherence of K88ac fimbrial E. coli to porcine small intestinal enterocytes but also neutralized cholera toxin and STa toxin. Data from this study demonstrated that K88ac fimbriae expressing LT and STa epitope antigens elicited neutralizing anti-toxin antibodies and anti-adhesin antibodies and suggested that E. coli fimbriae could serve as a platform for the development of broad-spectrum vaccines against ETEC.

Caco-2/TC7 cell line characterization for intestinal absorption: How reliable is this in vitro model for the prediction of the oral dose fraction absorbed in human?

Caco-2 cell line is one of the most used in vitro model to study intestinal absorption of compounds at screening level. Several clones have been isolated from Caco-2 cell line and characterized for their activities. Among them, TC7 clone was isolated from a late passage of the parental Caco-2 line and has shown to consist of a more homogeneous population with respect to the most representative functions of the small intestinal enterocytes, with more developed intercellular junctions. On the basis of these characteristics, it was selected within the framework of the EU A-Cute-Tox project to check its suitability to predict intestinal transport. In the present study, drugs, synthetic or natural chemicals have been characterized for their absorption profile in TC7 cells cultivated on semi-permeable filters for 21 days. The absorption experiments have been performed with the highest nontoxic concentration as determined in a preliminary set of cytotoxicity tests. The apparent permeability coefficient ( P app) has been extrapolated by calculating the passage of the test compound from the donor to the receiver compartment as a time function. The samples have been collected at different time intervals and the concentration of the test compounds analyzed by analytical methods (HPLC, GC, GC/MS). The P app obtained with the TC7 clone are comparable to those obtained with the parental cell line. However, some drawbacks related to the experimental system have been highlighted (i.e. low mass balance, adsorption to the plastics), on the basis of which some compounds were excluded from the analysis. In order to check the predictability of the model, a regression analysis has been performed by plotting P app values vs. the fraction absorbed in humans (FA, expressed as % of the administered dose). Additional elaborations have highlighted that the specific absorption pathway (passive, active and carrier-mediated) and other factors (i.e. efflux proteins and/or metabolic activity) can strongly affect the robustness of the prediction model. On the basis of the obtained results, TC7 clone has shown to be a model for passive diffusion as reliable as the parental cell line. However, we have remarked the non-suitability of the TC7 cells to predict intestinal absorption: (i) for highly lipophilic compounds; (ii) for poorly absorbed compounds; or (iii) when transporter-mediated routes and/or first pass metabolism are involved. The preliminary study of those factors likely influencing compound biokinetics, as well as the characterization of the cellular model with respect to metabolic and transporter competence, would help in the interpretation of data.

Colon luminal content and epithelial cell morphology are markedly modified in rats fed with a high-protein diet

Hyperproteic diets are used in human nutrition to obtain body weight reduction. Although increased protein ingestion results in an increased transfer of proteins from the small to the large intestine, there is little information on the consequences of the use of such diets on the composition of large intestine content and on epithelial cell morphology and metabolism. Rats were fed for 15 days with either a normoproteic (NP, 14% protein) or a hyperproteic isocaloric diet (HP, 53% protein), and absorptive colonocytes were observed by electron microscopy or isolated for enzyme activity studies. The colonic luminal content was recovered for biochemical analysis. Absorbing colonocytes were characterized by a 1.7-fold reduction in the height of the brush-border membranes (P = 0.0001) after HP diet consumption when compared with NP. This coincided in the whole colon content of HP animals with a 1.8-fold higher mass content (P = 0.0020), a 2.2-fold higher water content (P = 0.0240), a 5.2-fold higher protease activity (P = 0.0104), a 5.5-fold higher ammonia content (P = 0.0008), and a more than twofold higher propionate, valerate, isobutyrate, and isovalerate content (P < 0.05). The basal oxygen consumption of colonocytes was similar in the NP and HP groups, but ammonia was found to provoke a dose-dependent decrease of oxygen consumption in the isolated absorbing colonocytes. The activity of glutamine synthetase (which condenses ammonia and glutamate) was found to be much higher in colonocytes than in small intestine enterocytes and was 1.6-fold higher (P = 0.0304) in colonocytes isolated from HP animals than NP. Glutaminase activity remained unchanged. Thus hyperproteic diet ingestion causes marked changes both in the luminal environment of colonocytes and in the characteristics of these cells, demonstrating that hyperproteic diet interferes with colonocyte metabolism and morphology. Possible causal relationships between energy metabolism, reduced height of colonocyte brush-border membranes, and reduced water absorption are discussed.