SEARCH · Search PubMed

Results for “Intestinal barrier”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35Linked to original sources

PubMed1992

[Experimental damage of the epithelial layer of the ileum by dietary fats: transmission electron microscopy findings and their comparison with cell pathology in Crohn disease].

Regarding the unknown pathogenesis of Crohn's disease repeatedly the importance of diet has been accentuated. Epidemiological, biochemical and animal experimental results have focused on a possible relationship between the consumption of chemically processed, partial hydrogenated fats and the development of regional enteritis. In this context an experimental animal model in pigs was designed to analyze, whether transmission electron microscopic alterations of ileal mucosa could be induced by forage of chemically processed fats. By creation of a retroperistaltic ileal segment the contact time between chyme and intestinal mucosa was prolonged. Our underlying question was to what extent disorders of the intestinal barrier function could be compared to Crohn's disease. Present study concentrates on the epithelial-cell-layer. It was shown that in comparison to the control animals the lamina epithelialis mucosae of all animals after fat-feeding was characterized by: sublethal lesion of the enterocytes/crypt-epithelial cells (shortening and alteration of the microvilli, degeneration of mitochondria, formation of autophagocytic vacuoles); goblet cell hyperplasia and increased production of mucus; focal appearance of intraepithelial lymphocytes as well as presence of polymorphonuclear granulocytes in the epithelium; widening of the intercellular-space locally up to total loss of the functional structure of the epithelial-cell-layer. In total the picture can be evaluated as an inflammatory process of the ileal mucosa. It can be concluded, that chemically processed fats as used in the described experimental conditions could induce this process. The feature of mucosal damage shows obvious similarities to ultrastructural findings in Crohn's disease if compared.

Animals↗

PubMed2006

Interaction between miltefosine and amphotericin B: consequences for their activities towards intestinal epithelial cells and Leishmania donovani promastigotes in vitro.

The aim of this study was to evaluate the potential of a combination of two antileishmanial drugs, miltefosine (HePC) and amphotericin B (AMB), when administered by the oral route. Caco-2 cell monolayers were used as a validated in vitro model of the intestinal barrier and Leishmania donovani promastigotes as a model for evaluating the effect of the drug combination. Spectroscopic measurements demonstrated that HePC and AMB associate, leading to the formation of mixed aggregates in which AMB is solubilized as monomers. The incubation of the association of HePC and AMB with Caco-2 cell monolayers, at a concentration higher than 5 microM, led to (i) a reduction of the HePC-induced paracellular permeability enhancement in Caco-2 cell monolayers, (ii) an inhibition of the uptake of both drugs, and (iii) a decrease in the transepithelial transport of both drugs, suggesting that a pharmacokinetic antagonism between HePC and AMB could occur after their oral administration. However, the combination did not exhibit any antagonism or synergy in its antileishmanial activity. These results demonstrated a strong physicochemical interaction between HePC and AMB, depending on the concentration of each, which could have important consequences for their biological activities, if they are administered together.

Amphotericin B↗

PubMed2003

Obstructive jaundice alters proliferating cell nuclear antigen expression in rat small intestine.

Translocation of bacteria and endotoxin has long been documented in obstructive jaundice, and altered intestinal barrier function is considered to be one of the important mechanisms for this phenomenon. Proliferating cell nuclear antigen (PCNA), also known as cyclin, is an auxiliary protein of DNA polymerase-delta, and the level of synthesis correlates directly with rates of cellular proliferation and DNA synthesis. This study was designed with the aim of evaluating the effect of obstructive jaundice on PCNA expression in small bowel epithelium. Male Sprague-Dawley rats were randomized to four groups. Group A (n = 10, control group) underwent a sham operation. Group B (n = 9, obstructive jaundice group for 1 week) underwent common bile duct ligation. Group C (n = 8, obstructive jaundice group for 2 weeks) underwent common bile duct ligation. Group D (n = 8, obstructive jaundice group for 2 weeks) underwent common bile duct ligation with oral glutamine intake. After periods of 7 days and 2 weeks, segments of small bowel were harvested from groups A & B and groups C & D, respectively. Nuclear immunohistochemical expression of PCNA in small bowel was evaluated. The PCNA-labeling index [(PCNA-positive cells/500 cells) x 100] was quantified. Comparisons among the four groups were performed. The PCNA-labeling index in small bowel of group B was significantly higher than that of group A (29.0% vs 21.2%, p = 0.001). After 2 weeks of common bile duct ligation, the PCNA-labeling index in small bowel of group C was significantly lower than that of group A (19.4% vs 21.2%, p = 0.045). With oral glutamine intake daily, the PCNA-labeling index in small bowel of Group D was restored and was significantly higher than that of group A (24.5% vs 21.2%, p = 0.002). Obstructive jaundice for 1 week upgraded PCNA expression in rat small intestine. PCNA expression in rat small intestine later became depressed after obstructive jaundice for 2 weeks. Oral glutamine intake daily could effectively restore the PCNA expression in small bowel of rats subjected to obstructive jaundice for 2 weeks.

Animals↗

PubMed2005

Absorption of albumin by the midgut of a lepidopteran larva.

In the last decade, the study of peptide and protein absorption by the insect gut has received increasing attention because of the considerable impact this information may have on the development of new delivery strategies for insecticide macromolecules targeting haemocoelic receptors. Available experimental evidence in vivo suggests that, in insects, peptides and proteins can cross the intestinal barrier reaching the haemocoel, but the functional bases of this absorption pathway have not yet been thoroughly investigated. The current knowledge of the mechanisms involved in protein and polypeptide absorption in animals derives from the extensive studies performed in mammalian polarised epithelial cells, where the transcellular transport of proteins by transcytosis has been demonstrated. In this process, proteins are internalised at one pole of the cell and transported by cytoplasmic vesicular traffic to the opposite plasma membrane domain, where they are released with unchanged biological activity. Here we report data on albumin translocation across the isolated midgut of Bombyx mori caterpillars perfused in vitro. The functional properties of the transepithelial transport of this protein are described and, since absorption prevails over secretion, its lumen-to-haemolymph flux is characterised. Low-temperature incubations nearly abolish the transepithelial transport, while the peculiar physiological features of the larval midgut, i.e. the high lumen positive transepithelial voltage and the luminal alkaline pH, do not affect the flux. The obtained results indicate that albumin crosses B. mori larval midgut by transcytosis.

Albumins↗

PubMed2005

Differential modulation of ochratoxin A absorption across Caco-2 cells by dietary polyphenols, used at realistic intestinal concentrations.

The effect of polyphenols (PPs) on the absorption of ochratoxin A (OTA), a food-borne mycotoxin, was investigated in an in vitro model of the human intestinal barrier based on Caco-2 cells cultivated in a bicameral system. Two intraluminal concentrations of OTA approaching physiological levels were chosen (0.75 nM and 7.5 nM) through calculations based on estimated daily intakes. The transport of OTA from the apical to the basolateral side of Caco-2 cells, i.e. absorption, was directly proportional to its initial apical concentration. Very significant increase in both OTA absorption and cellular accumulation was observed upon co-incubation with certain PPs, i.e. chrysin, quercetin, genistein, biochanin A, resveratrol, at concentrations that should be encountered in the gastrointestinal tract, as well as with MK571, a specific inhibitor of MRPs efflux pumps. As these PPs have been reported to be metabolized in Caco-2 cells into substrates of MRP-2, we hypothesize that PPs and/or metabolites could impair the OTA efflux, previously proposed to be mediated by the MRP-2, through competitive inhibition for the pump. These data imply that interactions between OTA and PPs may lead to a greater bioavailability of the mycotoxin in the bloodstream with possible adverse effects for human health.

Biological Transport, Active↗

PubMed1999

Epithelial permeability to proteins in the noninflamed ileum of Crohn's disease?

BACKGROUND & AIMS: Crohn's disease (CD) is associated with a disturbed intestinal barrier. Permeability studies have focused on inert molecules, but little is known about transepithelial transport of macromolecules with antigenic potential in humans. The aim of this study was to quantify permeation and to characterize passage routes for macromolecules in ileal mucosa in CD. METHODS: Noninflamed and inflamed ileal mucosa specimens from patients with CD (n = 12) and ileal specimens from patients with colon cancer (n = 7) were studied regarding transmucosal permeation of ovalbumin, dextran (mol wt, 40,000), and 51Cr-EDTA for 90 minutes in vitro in Ussing chambers. Transepithelial passage routes for fluorescent ovalbumin and dextran 40,000 were investigated by confocal microscopy. RESULTS: Noninflamed ileum from CD patients showed increased permeation of ovalbumin compared with ileum from colon cancer patients (P < 0.05). Dextran permeation was equal in the three groups, whereas 51Cr-EDTA permeability was increased in inflamed ileum. Ovalbumin passed both transcellularly and paracellularly, but dextran followed a strictly paracellular route. Both markers were subsequently endocytosed by cells of the lamina propria. CONCLUSIONS: Noninflamed ileal mucosa from patients with CD shows increased epithelial permeability to ovalbumin, probably by augmented transcytosis. This increase in antigen load to the lamina propria could be an initiating pathogenic event in CD.

Adult↗

PubMed1993

Macrophage elimination increases bacterial translocation and gut-origin septicemia but attenuates symptoms and mortality rate in a model of systemic inflammation.

OBJECTIVE: The central question tested in this study was whether dichloromethylene-diphosphonate (CL2MDP) liposome-mediated elimination of hepatic and splenic macrophages would influence zymosan-induced bacterial translocation and the zymosan-induced generalized inflammatory response. SUMMARY BACKGROUND DATA: Both an uncontrolled activation of macrophages and the loss of intestinal barrier function have been implicated in the development of adult respiratory distress syndrome and multiple organ failure. METHODS: Macrophage elimination was accomplished by intravenous injection of 200 microL of CL2MDP-liposome suspension. Control mice received an intravenous injection of 200 microL of phosphate-buffered saline. Two days later, the animals were challenged intraperitoneally with zymosan suspended in paraffin to determine a dose-response curve (0.1, 0.5, or 1.0 mg/g body weight). Twenty-four hours after zymosan challenge, signs of systemic stress were determined, and bacterial translocation to the mesenteric lymph node, liver, spleen, and blood was measured. A separate mortality study was performed with a dose of 1.0 mg/g of zymosan suspension. RESULTS: The incidence of the systemic spread of bacteria was significantly increased in the macrophage-depleted mice. Although systemic bacterial translocation was promoted by macrophage elimination, the systemic toxic response was significantly decreased in all macrophage-depleted groups (p < or = 0.01). The 12-day mortality rate was 0% in the macrophage-depleted groups and 27% in the control group (p = 0.05). CONCLUSIONS: The lethal and toxic effects of zymosan appear to be related more to the excessive activation of macrophages than to the systemic spread of bacteria.

Animals↗

PubMed2000

Early nutrition and the development of immune function in the neonate.

The present review will concentrate on the development of the gut-associated lymphoid tissue and the role of early nutrition in promoting immune function. The intestine is the largest immune organ in the body, and as such is the location for the majority of lymphocytes and other immune effector cells. The intestine is exposed to vast quantities of dietary and microbial antigens, and is the most common portal of entry for pathogens, some of which are potentially lethal. The development of normal immune function of the intestine is therefore vital for survival, and is dependent on appropriate antigen exposure and processing, and also an intact intestinal barrier. In early life innate mechanisms of defence are probably more important than active or adaptive mechanisms in responding to an infectious challenge, since the healthy neonate is immunologically naïve (has not seen antigen) and has not acquired immunological memory. During this period maternal colostrum and milk can significantly augment resistance to enteric infections. The mechanisms of enhancing disease resistance are thought to be passive, involving a direct supply of anti-microbial factors, and active, by promoting the development of specific immune function. A tolerance response to dietary and non-invasive antigens is generally induced in the gut. However, it must also be able to mount an adequate immune response to ensure clearance of foreign antigens. It is now recognized that regulation of tolerance and active immune responses is critical to health, and failure to regulate these responses can lead to recurrent infections, inflammatory diseases and allergies. The education of the immune system in early life is thought to be critical in minimizing the occurrence of these immune-based disorders. During this phase of development maternal milk provides signals to the immune system that generate appropriate response and memory. One factor that has been proposed to contribute to the increase in the incidence of immune-based disorders, e.g. atopic diseases in Western countries, is thought to be the increased prevalence of formula-feeding.

Animals↗

PubMed1998

Characterization of furazolidone apical-related effects to human polarized intestinal cells.

In studying the effects of furazolidone (FZ) on the human intestinal Caco-2 cell line grown on microporous membrane, we have previously demonstrated a higher toxicity when the compound was administered at the apical (AP) side than at the basolateral (BL) side. Moreover, we have also shown the production, in the intact cells, of a nitroanion radical from FZ by a cytochrome c P450 reductase. The aim of the present study was to investigate which specific cell structures and functions are involved in the observed domain-related toxicity. The relevance of alterations in integrity and selective properties of the intestinal barrier as first-pass site for ingested molecules is also discussed. We have confirmed that, as expected, the Caco-2 cells are protected from FZ injury by a specific inhibitor of the cytochrome c P450 reductase, and we have shown that this protection is more active on the apical side of the cells. In sublethal conditions, FZ causes increased permeability to 3H-mannitol and, to a different extent, to 3H-inulin. Again the effect is higher when the cells are apically exposed. We have thus examined the tight junctions morphology: a disruption of the apical perijunctional actin-bound cytoskeleton was detected by rhodamine-phalloidin staining and microtubule disorganization by antitubulin fluoresceinated antibodies. Again, the effect was more evident when the cells were apically treated with FZ. Preferential transport and accumulation of the compound by active transport mechanisms could be excluded, since transport of FZ was linear and no intracellular accumulation was detected either from the AP and or the BL sides. All together these results may suggest that the AP formation of the active metabolite and its possible reactivity with SH groups of perijunctional microfilaments could be responsible of the higher FZ apical toxicity. This study shows that polarized differentiated cells are very interesting in vitro models to investigate specific cellular domains as targets of toxic effects and to detect subtle changes that may be induced, in absence of cell death, in specialized epithelial layers.

Actin Cytoskeleton↗

PubMed2000

Bacterial translocation during graft-versus-host disease after small bowel transplantation is reduced following inhibition of inducible nitric oxide synthesis.

BACKGROUND: Increased nitric oxide (NO) production may contribute to intestinal barrier dysfunction and increased bacterial translocation (BT). Since BT may play a major role in graft-versus-host disease (GVHD) after small bowel transplantation (SBTx), we evaluated the role of NO production in GVHD after SBTX in the rat. METHODS: Using the standard model of semiallogeneic SBTx in the rat, we prepared three experimental groups. Recipients in group 1 received LBNF1-LBNF1 transplants and were treated with aminoguanidine (AG) (200 mg/kg), recipients in group 2 received Lewis-LBNF1 grafts and were injected with saline, and recipients in group 3 received Lewis-LBNF1 transplants and AG (200 mg/kg). Urine nitrite/nitrate levels were measured daily, and BT was determined by culturing peritoneal swabs, mesenteric lymph nodes, spleen, liver, and blood. RESULTS: In group 1 we detected indefinite survival with normal histology. In group 2 a survival of 10.5 +/- 1.1 days was reached, and the typical histological features of acute GVHD were observed. The animals in group 3 showed a mean survival of 14.8 +/- 0.6 days (P<0.02 compared with group 2) and the histological features of acute GVHD, although with a prolonged time course. Comparing NO production and BT between groups 2 and 3 we detected significantly reduced NO production on postoperative days 2-9 (P<0.03) and significantly decreased BT on postoperative days 3 and 9 (P<0.03). CONCLUSION: Inhibition of inducible NO synthesis with AG reduces NO production, decreases BT, and prolongs survival during GVHD after SBTx and therefore may be a useful addition to standard treatment protocols for GVHD.

Animals↗

PubMed1999

Acquired interferon gamma responsiveness during Caco-2 cell differentiation: effects on iNOS gene expression.

BACKGROUND: Impairment of intestinal barrier function occurs under a variety of inflammatory conditions and is mediated at least in part by interferon gamma (IFN-gamma) induced nitric oxide (NO) production. Previous in vivo studies have shown that systemic lipopolysaccharide treatment caused an induction of the rat inducible nitric oxide synthase (iNOS) mRNA primarily in villus cells, rather than in undifferentiated crypt cells. AIMS: To examine iNOS induction by IFN-gamma in vitro as a function of enterocyte differentiation. METHODS: Preconfluent and postconfluent Caco-2 cells were treated with IFN-gamma in the presence or absence of various inhibitors. Northern analyses were performed to assess the magnitude of iNOS mRNA induction. IFN-gamma receptor mRNA and protein levels were determined. RESULTS: iNOS mRNA induction by IFN-gamma occurred at two hours and was not blocked by cycloheximide, indicating that it is an immediate early response. iNOS induction and nitrite/nitrate increases were inhibited by dexamethasone and pyrrolidine dithiocarbamate, supporting an important role for the NF-kappaB transcription factor in this process. The stimulated iNOS induction was seen almost exclusively under conditions of cellular differentiation-that is, in postconfluent Caco-2 cells. This increased IFN-gamma responsiveness seen in postconfluent Caco-2 cells correlated with an increased expression of IFN-gamma receptor, whereas T84 and HT-29 cells did not show any significant alterations in either iNOS induction or IFN-gamma receptor levels as a function of postconfluent growth. CONCLUSIONS: With regard to iNOS mRNA induction, IFN-gamma responsiveness is acquired during Caco-2 cell differentiation, perhaps related to an increase in the numbers of IFN-gamma receptors.

Blotting, Northern↗

PubMed1998

Expression of inducible nitric oxide synthase (iNOS) mRNA in inflamed esophageal and colonic mucosa in a pediatric population.

OBJECTIVE: Increasing evidence suggests that nitric oxide participates in the pathophysiology of intestinal barrier function/dysfunction and inflammation. Increases in inducible nitric oxide synthase (iNOS) mRNA and protein expression have been observed in colonic mucosal biopsies of adults with inflammatory bowel disease (IBD). It is unclear whether iNOS induction is specific for IBD or a reflection of nonspecific mucosal inflammation. Furthermore, the characteristics of iNOS mRNA expression in pediatric patients with gastrointestinal disorders remains ill-defined. Our objective was to examine the relationship between iNOS mRNA expression and gastrointestinal mucosal inflammation in a pediatric population. METHODS: Esophageal and colonic mucosal biopsies were obtained during endoscopy. Total RNA was isolated from these biopsies and reverse transcription-polymerase chain reaction (RT-PCR) performed (35 PCR cycles) using two 20-bp primers that amplified a predicted 372-bp conserved iNOS mRNA fragment. RESULTS: Biopsies were obtained from 29 children (22 boys; mean age 10.6 yr [range 1.7-16.5 yr]). Endoscopic and histological findings included normal esophageal mucosa (n = 3), esophagitis (n = 10), normal rectal mucosa (n = 2), ulcerative colitis (n = 10), and Crohn disease (n = 4). Evidence of iNOS mRNA was detected by PCR amplification in six of 10 patients with ulcerative colitis and in two of four patients with Crohn disease. However, iNOS mRNA was not amplified in any esophageal biopsy or in rectal mucosa biopsies with normal histology. CONCLUSIONS: These data indicate that upregulation of iNOS mRNA expression in colonic mucosa is a feature of IBD in children. iNOS mRNA expression is not upregulated in esophageal mucosa or in the absence of colonic inflammation. Further studies designed to determine the site- and cell-specificity of iNOS mRNA upregulation in mucosal biopsies from children with IBD may further illuminate the pathophysiology of these disorders.

Adolescent↗

PubMed2002

Human beta-defensin 2 but not beta-defensin 1 is expressed preferentially in colonic mucosa of inflammatory bowel disease.

OBJECTIVE: Various antimicrobial peptides such as defensins are part of innate immunity and contribute to the intestinal barrier that may be defective in inflammatory bowel disease (IBD). This study investigated beta-defensin mRNA and peptide expression in the colon from controls and patients with Crohn's disease, ulcerative colitis or unspecific colitis as inflammatory controls. METHODS: Mucosal mRNA expression was measured by multiplex reverse transcriptase-polymerase chain reaction (RT-PCR) with primers for human beta-defensin 1 (HBD-1) and human beta-defensin 2 (HBD-2) in CaCo-2 cells and in biopsies from 103 patients (33 controls, 24 Crohn's disease patients, 36 ulcerative colitis patients, 10 unspecific colitis patients). Paraffin-embedded tissue from colonic resections was tested for HBD-1 and HBD-2 peptides by immunohistochemistry. RESULTS: HBD-1 mRNA was expressed constitutively whereas HBD-2 was induced by pro-inflammatory cytokines in CaCo-2 cells. HBD-1 mRNA was detectable in 61% of control and Crohn's disease biopsies and 53% of ulcerative colitis biopsies. HBD-2 transcript was expressed differentially, with 18% of control biopsies positive as opposed to 34% in Crohn's disease and 53% in ulcerative colitis. HBD-2 mRNA but not HBD-1 mRNA was expressed preferentially in inflamed areas. Immunohistochemical investigation demonstrated the presence of defensin peptides in colonic epithelium as well as the differential induction in IBD. CONCLUSIONS: HBD-1 is expressed constitutively in colonic tissue irrespective of inflammation. HBD-2 is barely present in uninflamed colon but it is induced in inflammation. The lower expression of HBD-2 in Crohn's disease compared with ulcerative colitis indicates different responses of the mucosal innate defence. Defensins may play a crucial role in controlling pathogen invasion in IBD, although the functional significance remains to be established.

Cells, Cultured↗

PubMed1976

[Epithelial barriers of the intestine. Significance and function in defense against infection].

The epithelial surface of the intestinal tract provides for an important barrier between the organism and its environment. However, it permits the passage into the tissues of limited amounts of macromolecules and/or particles, especially bacteria. These functions are age- and species-dependent, and they are closely related to nonspecific and specific immune reactions. Continuous and intimate contact between antigenic material from the gut lumen and immunocompetent cells takes place in gut-associated lymphoid tissues.

Bacterial Infections↗

PubMed2004

Burn injury sensitizes rat Kupffer cells via mechanisms dependent on gut-derived endotoxin.

BACKGROUND: Bacterial translocation occurs after thermal injury in association with intestinal barrier loss. Recently, we found that sensitization of Kupffer cells involved gut-derived endotoxin; therefore, the purpose of this work was to study the mechanisms of sensitization of Kupffer cells in burn injury. METHODS: Rats received a 30% body surface area full-thickness steam burn 24 h before experiments. Serum alanine aminotransferase (ALT) was measured to assess liver damage, and plasma endotoxin in the portal vein were measured. Kupffer cells were isolated 24 h after the burn. Intracellular calcium ([Ca2+]i) in Kupffer cells was measured using a microspectrofluorometer with the fluorescent indicator, fura-2, and tumor necrosis factor (TNF)-alpha was measured by enzyme-linked immunosorbent assay (ELISA). RESULTS: Lipopolysaccharide (LPS)-induced mortality was increased by burn treatment. This increase was blocked by gadolinium chloride, a Kupffer-cell toxicant. Accordingly, Kupffer cells were involved in this system. The LPS-induced increase of ALT was upregulated by the burn injury. This increase was blocked by pretreatment with antibiotics. Endotoxin levels were increased to almost 300 pg/ml (normal, <20 pg/ml) in the portal veins of rats that received a burn. This increase was blunted by antibiotics. In Kupffer cells isolated from untreated control rats, [Ca2+]i increased to 82+/-7 nM after the addition of LPS (100 ng/ml). Levels were elevated twofold over control levels in the cells from rats with burn (174+/-15 nM). In addition, TNF-alpha production by Kupffer cells isolated from rats with burn was increased fourfold over the based level. Sterilization of the gut with antibiotics completely blocked all effects of the burn on [Ca2+]i and TNF-alpha release. CONCLUSIONS: Kupffer cells isolated from rats with burn exhibited sensitization to LPS, involving gut-derived endotoxin. It is concluded that burns sensitize Kupffer cells to LPS via mechanisms that are dependent on gut-derived endotoxin.

Animals↗

PubMed1974

The intestinal absorption of dietary cholesterol by hypercholesterolemic (type II) and normocholesterolemic humans.

The incomplete absorption of dietary cholesterol may represent an adaptive intestinal barrier that prevents hypercholesterolemia. To explore this mechanism, we compared cholesterol absorption in 15 normocholesterolemic and 6 hypercholesterolemic (type II) subjects fed background cholesterol-free formula diets with 40% of calories as fat. Each test meal consisted of a breakfast into which was incorporated scrambled egg yolk containing 300-500 mg of cholesterol and [4-(14)C]cholesterol (3-22 muCi), either naturally incorporated into the yolk cholesterol by previous isotope injection into the laying hen or added in peanut oil to the yolk of the test breakfast. In some instances [1alpha-(3)H]cholesterol was the radioactive marker. The radioactivity of the fecal neutral sterol fraction was determined in daily stool samples for the next 7 days to provide an estimate of unabsorbed dietary cholesterol. The amount of absorbed and reexcreted labeled cholesterol proved negligible. Most unabsorbed dietary cholesterol appeared in the stool on the second or third day after the meal, and 95% or more was recovered in the stool by 6 days. Plasma specific activity curves were usually maximal at 48 h. Normal subjects absorbed 44.5+/-9.3 (SD) of the administered cholesterol (range 25.9-60.3). Hypercholesterolemics absorbed the same percentage of cholesterol as normals: 47.6+/-12.6% (range 29.3-67.3). Absorption was similar whether the radiolabeled cholesterol was added to egg yolk or naturally incorporated in it (42.1+/-9.3 vs. 48.9+/-9.8%). Six normal subjects were fed a cholesterol-free formula for 4 wk, and then different amounts of cholesterol (110-610 mg/day) were added for another 4 wk. At the end of each period, single test meals containing either 110, 310, or 610 mg of cholesterol and [1alpha-(3)H]cholesterol were administered. Cholesterol absorption was 42.3+/-6.0% and 45.4+/-8.3% for the two dietary periods, respectively. The absolute cholesterol absorption was linearly related to the amount of cholesterol in the test meal, and absorption was not affected by background diets high or low in cholesterol content.

Adult↗

PubMed2026

Phytolacca acinosa Roxb. induces intestinal toxicity through the histamine-MLCK-tight junction axis: Integrated evidence from proteomics, metabolomics, intestinal organoids and epithelial barrier validation.

Phytolacca acinosa Roxb. (PR) is a saponin-rich medicinal plant associated with gastrointestinal toxicity, but the mechanisms underlying PR-induced intestinal barrier injury remain unclear. In this study, raw PR extract was analytically characterized by UPLC-ZenoTOF-MS/MS, confirming triterpenoid saponins as the predominant constituents. C57BL/6 J mice were orally exposed to characterized PR extract (1.20 or 12.0 g/kg for 5 h), and Caco-2 cells and mouse intestinal organoids were used to assess epithelial toxicity and barrier disruption. Histopathology, ELISA, FITC-dextran permeability assays, immunofluorescence, CCK-8, LDH release, western blotting, DIA-based proteomics and untargeted metabolomics were integrated to define toxicological mechanisms. PR induced dose-dependent intestinal inflammation and barrier dysfunction, with the ileum as the most sensitive target. PR increased serum DAO and D-lactate and intestinal TNF-α and IL-1β, disrupted organoid morphology, enhanced epithelial permeability, and reduced ZO-1 expression. Proteomics revealed changes in inflammatory, lipid-metabolic, cytoskeletal and tight-junction pathways, including upregulation of MLCK3 and phospholipase-related proteins and downregulation of ZO-1 and ZO-2. Metabolomics identified histidine metabolism disturbance and histamine accumulation. Integrated multi-omics and pharmacological validation indicated that histamine activated the PLC/IP₃/Ca²⁺/CaM/MLCK cascade, promoting MLC phosphorylation, tight-junction disassembly and epithelial leakiness. MLCK inhibition partially restored ZO-1/ZO-2 expression and attenuated PR-induced epithelial injury. These findings identify the histamine-MLCK-tight junction axis as a key mechanism of PR-induced intestinal toxicity and support hazard identification of saponin-rich PR exposure.

Animals↗

PubMed2006

What can we learn from the oral intake of prions by sheep?

The central nervous system is the ultimate target of prions, the agents responsible for fatal neurodegenerative diseases known as transmissible spongiform encephalopathies (TSEs). The neuro-invasive phase and its related clinical signs take place after a long incubation period. During this asymptomatic phase, however, active transport and replication of the infectious agent take place in peripheral sites. The oral infection route has been extensively studied because of its implication in the recent epidemic of bovine spongiform encephalopathy (BSE) in cattle and of the resulting human cases of variant Creutzfeldt-Jakob disease (vCJD). Rodent models have been useful in studying some aspects of this pathogenesis. Now, new data on the initial steps of oral infection have been obtained in sheep. This species is naturally infected with scrapie by horizontal transmission and there is strong evidence implicating the oral route. Furthermore, the existence of resistant and susceptible genotypes offers the possibility of comparative studies. The data were obtained using surgical and biochemical procedures to modulate the efficiency of oral infection and show that, in sheep, the abnormal prion protein (PrP) associated with the infectious agent crosses the intact intestinal barrier at the level of the enterocytes and then passes rapidly into lymph. These steps are identical in susceptible and resistant sheep. Thereafter, replication takes place in lymphoid structures. Other results in the same study indicate that alimentary fluids almost completely degrade the PrP of the inoculum. Though not directly transposable to human diseases, in which it is not possible to study these early stages, these data allow the elaboration of a simplified concept for the pathogenesis of TSEs. They also suggest that human contamination at the level of the oral cavity might be more important than previously suspected.

Administration, Oral↗