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PubMed2005

[Tumor necrosis factor alpha and enterocyte apoptosis in mice with fulminant hepatic failure].

OBJECTIVE: To study the role of tumor necrosis factor-alpha (TNFalpha) on enterocyte apoptosis in the experimental model of fulminant hepatic failure (FHF). METHODS: Liver damage was induced by lipopolysaccharide (LPS)/TNFalpha in D-galactosamine (GalN) sensitized BALB/c mice. Serum TNFalpha levels were determined by enzyme-linked immunosorbent assays (ELISA). The intestinal tissues were studied micro- and ultra-microscopically at 2 h, 6 h, 9 h, 12 h and 24 h time points in mice with fulminant hepatic failure. Enterocyte apoptosis was determined by TUNEL method. The TNFR I expression in the intestinal tissue was tested by immunohistochemistry. RESULTS: (1) Gut mucosa was morphologically normal at every time point in all groups, but typical apoptotic cells could be seen in the experimental groups under the electron microscope. Apoptosis rate of gut mucosal epithelial cells was significantly increased at 6 h (large intestine: 6.47e(-3)+/-2.91e(-4); small intestine: 6.64e(-3)+/-3.78e(-4)), 9 h (large intestine: 6.81e(+4)+/-7.41e(+3); small intestine: 2.58e(+4)+/-2.28e(+3)) and 12 h (large intestine: 4.92e(+4)+/-9.80e(+3); small intestine: 5.24e(+4)+/-3.01e(+3)), and peaked at 12 h in mice with FHF. (2) TNFalpha induced apoptosis of enterocytes in mice with FHF. Anti-TNFalpha inhibited this effect. (3) The integrated OD (IOD) levels of TNFalpha receptor I protein expressed differently in the intestine of mice with GalN/LPS and GalN/ TNFalpha-induced FHF at 9 h after GalN/LPS and GalN/ TNFalpha administration, in comparison with those of the control groups. IOD level of TNFRI changed significantly at 6 h (large intestine: 2.82e(+4)+/-4.60e(+3); small intestine: 1.14e(+4)+/-2.13e(+3)), 9 h (large intestine: 6.81e(+4)+/-7.41e(+3); small intestine: 2.58e(+4)+/-2.28e(+3)) and 12 (large intestine: 4.92e(+4)+/-9.80e(+3); small intestine: 5.24e(+4)+/-3.01e(+3)) hours after GalN/LPS and GalN/ TNFa administration. The expression of TNFR1 protein was significantly higher at 9 and 12 h after GalN/LPS and GalN/TNFa administration than other time points. Protein expression of TNFR1 was positively correlated with enterocyte apoptosis. CONCLUSION: TNFa can induce enterocyte apoptosis in mice with FHF. Anti- TNFalpha IgG can inhibit this role. Excessive TNFRI expression of enterocyte in fulminant hepatic failure can be induced by TNFa, which suggests that TNFalpha can induce apoptosis of enterocyte by up-regulation of TNFRI protein expression.

Animals↗
PubMed1998

Caco-2 cells express a combination of colonocyte and enterocyte phenotypes.

Caco-2 cells are derived from a human colonic adenocarcinoma, but differentiate into small intestinal-like cells after confluence. While this enterocytic differentiation has been well studied, the presumed parallel loss of colonocyte function has not been as thoroughly examined. To follow the phenotype for both tissues, Western blots were performed using antisera recognizing liver/bone/kidney alkaline phosphatase and surfactant-like particle proteins found in normal human colon, along with antisera against the small bowel representatives of the same proteins. Antisera against proteins enriched in either enterocytes (alpha1-antitrypsin) or colonocytes (surfactant protein A) were also evaluated. Alkaline phosphatase activity increased from 3 to 18 days post-confluence. Activity at 3 days post-confluence derived substantially from both isomers. Thereafter, the colonic (liver/bone/kidney) isomer declined to low levels as the content of the enterocytic isomer rose. A similar pattern was found with colonic (decreasing expression) and enterocytic (increasing expression) surfactant-like particle proteins. In particular, the content of larger enterocytic particle proteins (97 and 116 kDa) increased with time in culture. Expression of alpha1-antitrypsin increased early and remained high, whereas surfactant protein A generally declined after the third day post-confluency. In summary, undifferentiated Caco-2 cells express very low levels of proteins characteristic of either colonocytes or enterocytes. Immediately after confluence, they expressed proteins characteristic of both cell types. Thereafter, the content of colonocyte-specific proteins decreased, whereas those specific for the enterocyte increased. The timing and degree of this phenotypic switch have implications for the interpretation of experiments using Caco-2 cells as a model of small intestinal function.

Alkaline Phosphatase↗
PubMed1998

TNF-induced enterocyte apoptosis in mice is mediated by the TNF receptor 1 and does not require p53.

Injection of recombinant mouse TNF into mice is known to induce a shrinkage of the duodenal villi, which becomes evident 30-90 min later and is associated with a detachment of enterocytes in the lumen. These cells can be collected by lavage and are all apoptotic, i.e. hypodiploid as seen by flow cytometric analysis. Thus the count of detached cells was used as an evaluation of the TNF-induced cell loss and apoptosis in the mucosa. TNF injection induced a cell loss of similar magnitude in wild-type (+/+) or in mice lacking the TNF receptor (TNFR)2 (p75, TNFR2-/-), while mice lacking the TNFR1 (p55, TNFR1-/-) were completely resistant to this effect. TNF increased the expression of p53 tumor suppressor gene in the enterocytes from the crypts but not from the villi, as seen by Western blots and histochemistry. TNF increased the expression of p53 in both TNFR2-/- and TNFR1-/- mice. Furthermore, enterocyte cell loss was not attenuated in p53-/- mice. The results indicate that TNF, acting on its receptor 1, induces an apoptotic detachment of the enterocytes from the tip of the villi (i.e. the old enterocytes), while in the enterocytes from the crypts (the young enterocytes) TNF increases, via either TNFR1 or TNFR2, the expression of p53, without inducing apoptosis.

Animals↗
PubMed1985

Selective expression of brush border hydrolases by mouse Peyer's patch and jejunal villus enterocytes.

Developmental profiles describing the expression of lactase, alpha-glucosidase, and alkaline phosphatase activities have been determined quantitatively in mouse jejunal enterocytes during migration over villi and Peyer's patch lymphoid tissue. The predicted maximal lactase and alpha-glucosidase activities expressed by enterocytes migrating over Peyer's patch follicles were about one-quarter and one-half of values found in control villi. Alkaline phosphatase activity was, on the other hand, one third greater in Peyer's patch compared with villus enterocytes. Expression of lactase and alpha-glucosidase activities was initially less in enterocytes migrating along interfollicular compared with control villi. Subsequent increase in hydrolase activities occurred during the later stages of enterocyte migration over interfollicular villi. Lactase activity in athymic mice Peyer's patch enterocytes was identical to that recorded for control mice. The corresponding value for villus lactase was, however, only half that found in control tissue. Factors produced locally in lymphoid follicles are probably responsible for selective effects on enterocyte differentiation.

Alkaline Phosphatase↗
PubMed1996

Binding of enterotoxigenic Escherichia coli expressing different colonization factors to tissue-cultured Caco-2 cells and to isolated human enterocytes.

The binding of ETEC strains expressing different colonization factors to the human enterocyte-like cell line Caco-2 and to isolated human enterocytes were determined. Strains expressing CFA/I, CS2, CS4+CS6, CS5+CS6, CS7, CFA/III+CS6 and PCFO166 adhered well to both types of cells whereas bacteria producing CS1, CS6 only, or CS17 did not adhere to either Caco-2 cells or to jejunal human enterocytes, suggesting that similar binding structures are present in both cell types. However, in some instances, binding of bacteria to the two types of cells differed, e.g. bacteria expressing CS3 or PCFO9 bound well to human enterocytes but not to Caco-2 cells. Conversely, bacteria producing PCFO20 or PCFO159 only adhered to Caco-2 cells and not to jejunal enterocytes. With few exceptions, this inability to bind to human enterocytes was the same for cells from all parts of the small intestine. This study contradicts previous reports suggesting that the binding structures of Caco-2 cells are identical to those of human enterocytes.

Bacterial Adhesion↗
PubMed1991

Rat enterocyte injury by oxygen-dependent processes.

Neutrophils migrate to areas of inflammation and, when stimulated, produce O2-, H2O2, and other reactive O2 metabolites. To assess the effects of stimulated neutrophils on enterocytes, rat enterocytes were incubated with peripheral neutrophils. To assess cell viability, trypan blue exclusion and lactate dehydrogenase and protein release were measured. When 10(6) enterocytes/mL were incubated with 2.5 x 10(5) neutrophils/mL stimulated with phorbol myristate acetate, trypan blue exclusion decreased and lactate dehydrogenase and protein release increased. With the addition of 0.10 mg/mL of superoxide dismutase, trypan blue exclusion further decreased and lactate dehydrogenase and protein release increased. This suggests that H2O2- or H2O2/O2(-)-derived metabolites are more damaging to isolated enterocytes than O2-. To test this hypothesis, enterocytes were incubated with xanthine and increasing concentrations of xanthine oxidase in the presence and absence of superoxide dismutase. With increasing concentrations of xanthine oxidase, the cell number decreased and protein release increased. With the addition of superoxide dismutase, fewer cells were present, suggesting that cell lysis occurred. Protein release was further increased by the addition of superoxide dismutase. Enterocytes were then incubated with leucine and increasing concentrations of amino acid oxidase. With increasing concentrations of amino acid oxidase, trypan blue exclusion decreased and protein and lactate dehydrogenase release increased. These effects were ameliorated by the addition of 500 IU catalase/mL. These data suggest that O2- and H2O2, whether created by stimulated neutrophils or an enzyme-generating system, are damaging to isolated enterocytes. Superoxide dismutase did not offer enterocytes protection.

Animals↗
PubMed1986

Interaction of epidermal growth factor with specific binding sites of enterocytes isolated from rat small intestine during development.

Isolated enterocytes from rat small intestine were characterized for their specific binding of epidermal growth factor (EGF). Intestinal epithelial cells were isolated at 4 degrees C to minimize the loss of receptor sites during the isolation procedure. 125I-labelled EGF binding to enterocytes from adult rats was found to be specific, saturable, temperature dependent and trypsin sensitive. Binding performed in the presence of a lysosomotropic agent (NH4Cl) increased the time required to reach maximal binding at 25 degrees C. NH4Cl had no significant effect on the time-course of EGF binding at 4 degrees C and 37 degrees C. A Scatchard plot showed a curvilinear relationship indicating that EGF binds to enterocytes with more than one binding site. Developmentally, enterocytes from fetuses and pups showed characteristic temperature dependence and trypsin sensitivity, but with different levels of binding to EGF. Specific EGF binding was demonstrably higher in enterocytes from small intestine of term fetuses. EGF binding to isolated enterocytes declined rapidly after birth, and the level stayed fairly constant thereafter. Pretreatment of enterocytes from fetal intestine with mature rat milk led to a dose-dependent decrease in EGF binding. These results suggest the presence of endogenous milk factors that modify EGF binding and account for, at least partly, the observed rapid decrease of EGF binding after birth.

Age Factors↗
PubMed1990

Concurrent infection of enterocytes with Eimeria scabra and other enteropathogens in swine.

Bacteria were detected in the enterocytes of the distal jejunum in weaned pigs on Days 7 and 9 post-infection (DPI) with Eimeria scabra in addition to the developmental stages of the coccidia. Short rod-shaped bacteria were identified in approximately 60% of the enterocytes that contained developmental stages of E. scabra. No such bacteria were observed in cells where coccidia were absent. Gamonts of cryptosporidia were also observed within the microvillous zone of the enterocytes in the distal jejunum of weaned pigs on DPI 9 with E. scabra. Cryptosporidia were present only in enterocytes harbouring stages of E. scabra. Chlamydial particles were also found in the cytoplasm of enterocytes 7 DPI with E. scabra. The presence of other enteropathogens exclusively in the enterocytes containing developmental stages of coccidia suggests that the coccidium E. scabra facilitates the invasion and development of bacteria, cryptosporidia and chlamydia in the enterocytes.

Animals↗
PubMed1991

Iron binding to, and release from, the basolateral membrane of mouse duodenal enterocytes.

The basolateral membrane of mouse duodenal enterocytes can be selectively labelled in vitro with 59Fe by incubating intact enterocytes with 59Fe(III)-nitrilotriacetate at 0-4 degrees C. It has been proposed that this labelling represents binding to a site important in the transfer of intracellular Fe to the portal plasma (Snape, S., Simpson, R.J. and Peters, T.J. (1990) Cell Biochem. Funct. 8, 107-115). Studies presented here show binding to intact enterocytes in vitro was complete within 1 h and was proportional to enterocyte protein concentration. Binding to enterocytes isolated from both normal and chronically hypoxic mice showed a hyperbolic dependence on medium Fe(III) concentration, consistent with a single class of binding sites. Neither apparent binding constant nor maximal binding were increased by hypoxic exposure of mice, suggesting that the increased in vivo labelling of this site in hypoxia is not due to an increase in affinity or capacity of this site for iron. Release of iron from intact enterocytes, labelled at 0-4 degrees C, was measured at 37 degrees C and 0-4 degrees C. Release of 59Fe was extensive and more rapid at 37 degrees C with highest release to mouse serum. Iron released to serum was found to be bound to transferrin. Prior dialysis of serum against buffer led to complete failure of enterocytes to release iron. Reconstituting serum by adding back the dialysate restores release to levels seen in fresh serum, suggesting that low molecular weight serum components, notably bicarbonate, mediate iron transfer from the basolateral membrane to serum transferrin. The properties of the basolateral membrane iron binding site described here are consistent with a role in the iron transfer process.

Animals↗
PubMed1999

The effect of epidermal growth factor on differentiation of isolated enterocytes after small bowel resection.

BACKGROUND/PURPOSE: In previous studies using mucosal scrapings or whole-bowel homogenates, epidermal growth factor (EGF) augments adaptation after massive small bowel resection (SBR). The purpose of this study was to determine directly the effect of adaptation and EGF on enterocyte differentiation using an explicit enterocyte cell population. METHODS: Male ICR mice underwent 50% proximal SBR or sham (bowel transection-reanastomosis) and were selected randomly to either orogastric saline or EGF (50 microg/kg/d). After 3 days, enterocytes were isolated from the remnant ileum by mechanical vibration and assayed for DNA and protein content as well as sucrase and alkaline phosphatase (AlkP) activity. RESULTS: Ileal wet weight, enterocyte protein, and DNA content were increased significantly after SBR and boosted even further with EGF. When normalized for protein, SBR caused an increase in AlkP and sucrase activity, and EGF treatment caused AlkP and sucrase activity to return to baseline. CONCLUSIONS: EGF enhances adaptation; however, when normalized for protein, the activity of two enterocyte-specific enzymes was not significantly altered by EGF. This analysis of an explicit enterocyte population supports the notion that the beneficial effects of EGF are more likely caused by increased numbers of enterocytes rather than an increase in the functional activity of each individual cell.

Adaptation, Physiological↗
PubMed1997

Synthesis of citrate from phosphoenolpyruvate and acetylcarnitine by mitochondria from rabbit enterocytes: implications for lipogenesis.

Enterocytes from fasted rabbits make glucose from exogenous fructose and dihydroxyacetone at rates of 180 and 91 nmol/min/10(8) cells but do not make glucose from glycerol, aspartate, malate, lactate, alpha-ketoglutarate, glutamate or glutamine. Total activities of phosphoenolpyruvate carboxykinase, fructose 1,6-bisphosphatase and glucose 6-phosphatase in isolated enterocytes are 0.44, 0.60 and 1.90 mumol/min/10(8) cells, and > or = 95% of carboxykinase activity is intramitochondrial. Enterocytes contain marginal glycerol kinase (0.05 mumol/ min/10(8) cells) and essentially no pyruvate carboxylase activities. Enterocyte mitochondria synthesize citrate from exogenous phosphoenolpyruvate and acetylcarnitine at a rate of 2.40 nmol/min/mg protein. Citrate formation is highly dependent on exogenous HCO3 and inhibited strongly by 3-mercaptopicolinate and 1,2,3-benzenetricarboxylate. Citrate synthesis is stimulated consistently by GDP and significantly so by GTP. Citrate production is unaffected by ADP or ATP. Enterocytes from fasted-refed rabbits contain activities of 0.05, 0.12, 0.39 and 0.56 mumol/min/mg cytosolic protein of ATP:citrate lyase, NADP:malate dehydrogenase, glucose 6-phosphate dehydrogenase and NADP:isocitrate dehydrogenase. Activities of NADP:malate dehydrogenase, glucose 6-phosphate dehydrogenase and NADP:isocitrate dehydrogenase are significantly higher in enterocytes from fasted-refed rabbits than those from fasted rabbits. Mitochondrial phosphoenolpyruvate carboxykinase in enterocytes in vivo could convert glycolysis-derived phosphoenolpyruvate to oxaloacetate that, with acetyl CoA, could form citrate for export to support cytosolic lipogenesis as an activator of acetyl CoA carboxylase, a source of carbon via ATP:citrate lyase and of NADPH via NADP:malate dehydrogenase or NADP:isocitrate dehydrogenase.

Acetylcarnitine↗
PubMed1998

Compartmentation and kinetics of urea cycle enzymes in porcine enterocytes.

We have recently reported the synthesis of urea from ammonia, glutamine and arginine in enterocytes of postweaning pigs. The present study was conducted to determine the compartmentation and kinetics of urea cycle enzymes in these cells. Carbamoyl phosphate synthase I (CPS I) and ornithine carbamoyltransferase (OCT) were located exclusively in mitochondria, whereas argininosuccinate synthase (ASS) and argininosuccinate lyase (ASL) were found in the cytosol. Arginase isozymes were present in both the cytosol and mitochondria of enterocytes, and differed in their sensitivity to heat inactivation. Except for OCT, Vmax values of urea cycle enzymes were much lower in enterocytes than in the liver of pigs, and vice versa for their Km values. Because of a low rate of ureagenesis in enterocytes compared with the liver, intestinal urea cycle enzymes may function primarily to synthesize citrulline. The co-localization of CPS I and OCT and a high activity of OCT in enterocyte mitochondria favors the intestinal synthesis of citrulline from ammonia, HCO3- and ornithine. Low activities of cytosolic ASS and ASL minimize the conversion of citrulline into arginine and therefore, the recycling of citrulline into ornithine via arginase in postweaning-pig enterocytes. These kinetic properties of intestinal urea cycle enzymes maximize the net synthesis of citrulline from glutamine and explain the release of large amounts of citrulline by the pig small intestine. The two compartmentally separated arginase isozymes in enterocytes may play an important role in regulating the intestinal metabolism of proline, nitric oxide and polyamines.

Animals↗
PubMed1997

Luminal trypsin may regulate enterocytes through proteinase-activated receptor 2.

Proteinase-activated receptor 2 (PAR-2) is a recently characterized G-protein coupled receptor that is cleaved and activated by pancreatic trypsin. Trypsin is usually considered a digestive enzyme in the intestinal lumen. We examined the hypothesis that trypsin, at concentrations normally present in the lumen of the small intestine, is also a signaling molecule that specifically regulates enterocytes by activating PAR-2. PAR-2 mRNA was highly expressed in the mucosa of the small intestine and in an enterocyte cell line. Immunoreactive PAR-2 was detected at the apical membrane of enterocytes, where it could be cleaved by luminal trypsin. Physiological concentrations of pancreatic trypsin and a peptide corresponding to the tethered ligand of PAR-2, which is exposed by trypsin cleavage, stimulated generation of inositol 1,4,5-trisphosphate, arachidonic acid release, and secretion of prostaglandin E2 and F1alpha from enterocytes and a transfected cell line. Application of trypsin to the apical membrane of enterocytes and to the mucosal surface of everted sacs of jejunum also stimulated prostaglandin E2 secretion. Thus, luminal trypsin activates PAR-2 at the apical membrane of enterocytes to stimulate secretion of eicosanoids, which regulate multiple cell types in a paracrine and autocrine manner. We conclude that trypsin is a signaling molecule that specifically regulates enterocytes by triggering PAR-2.

Animals↗
PubMed1995

Exposure of the lateral enterocyte membrane by dissociation of calcium-dependent junctional complex augments endocytosis of enteric bacteria.

Intestinal bacterial translocation is facilitated in a variety of clinical conditions involving increased intestinal permeability, such as shock and trauma. Because there is both in vivo and in vitro evidence that enteric bacteria can be internalized by intestinal epithelial cells, experiments were designed to test the effect of increased intestinal permeability on enterocyte endocytosis of enteric bacteria. Mature, confluent cultures of HT-29 enterocytes were placed in a calcium-free solution for 1 h. Enterocyte viability was not noticeably altered, but transepithelial electrical resistance was significantly decreased (indicating a decrease in epithelial junctional integrity), and the enterocytes were pulled apart. Electron microscopic observations revealed enteric bacteria preferentially adherent on the exposed enterocyte lateral surface, and the numbers of viable enteric bacteria (Listeria monocytogenes, Salmonella typhimurium, Proteus mirabilis, Escherichia coli, and Enterococcus faecalis) internalized by these enterocytes were significantly increased. Restoration of calcium restored confluency to enterocyte cultures, and bacterial internalization reverted to control levels. Thus, calcium-dependent junctional integrity might play a role in augmenting bacterial translocation in clinical conditions associated with increased intestinal permeability.

Animals↗
PubMed1987

Adherence of Salmonella typhimurium to small-intestinal enterocytes of the rat.

The adherence of radiolabeled Salmonella typhimurium to freshly isolated enterocytes of rats was studied. The results established that type 1 fimbriated strains adhered in significantly higher numbers than did related nonfimbriated strains. Adherence was inhibited by D-mannose and methyl alpha-D-mannoside. Results of kinetic studies indicated that adherence was biphasic; the number of bacteria that adhered per enterocyte remained constant for approximately 20 min and then increased rapidly under the assay conditions. The second phase was associated with structural damage to the enterocytes. The addition of chloramphenicol did not prevent the initial attachment of bacteria to enterocytes but did prevent the second phase. Viable and nonviable bacterial cells adhered to enterocytes, but only viable bacteria were destructive. Freshly isolated enterocytes (trypan blue impermeable) and enterocytes stored overnight (trypan blue permeable) were infected by viable S. typhimurium in a similar manner, suggesting that metabolic activity of the host cell was of less consequence than metabolic activity of the bacterial cells. A model for the role of mannose-sensitive fimbriae as a virulence factor is proposed.

Animals↗
PubMed1998

Human intestinal M cells exhibit enterocyte-like intermediate filaments.

BACKGROUND: The derivation and ultrastructural composition of M cells covering the lymphoid follicles of Peyer's patches is still unknown. Results from different animal models have shown that there are species specific differences in the composition of intermediate filaments between M cells and neighbouring enterocytes. Little is known, however, about intermediate filaments of human M cells. AIMS: To compare components of the cytoskeleton of human M cells with those of adjacent absorptive enterocytes. METHODS: The expression and localisation of different cytokeratins, vimentin, and desmin in M cells was determined on follicle associated epithelia of human appendix using immunohistochemistry and immunogold electron microscopy. RESULTS: Cytokeratins specific for human intestinal epithelial cells such as cytokeratins 8, 18, 19, and 20 were expressed in both absorptive enterocytes and M cells with no differences in intensity and cellular distribution between both cell types. Vimentin and desmin, tissue specific markers of either mesenchymal or myogenic cells, as well as other cytokeratins were not detectable in enterocytes or M cells. CONCLUSION: This is the first study on the structure of intermediate filaments in human intestinal M cells. Our results show that in contrast to several animal models, human M cells apparently do not differ from adjacent enterocytes in the composition of their intermediate filament cytoskeleton. The presence of enterocyte like cytokeratins and the absence of other cytokeratins as well as of vimentin and desmin supports the hypothesis of an epithelial origin of human intestinal M cells and suggests that M cells may derive from differentiated enterocytes.

Adult↗
PubMed1995

The involvement of macrophages and lymphocytes in the apoptosis of enterocytes.

Epithelial cells of the gut are characterized by rapid, constant cell renewal. The death of epithelial cells at the villus tips occurs so regularly that it must be regarded as a well-controlled cell death, designated as apoptosis. However, only limited information has been available on the mechanism of this phenomenon, including the disposal of the effete cells. In the small intestine of the guinea pig and monkey, macrophages are densely aggregated at the lamina propria of the villus tips and vigorously engaged in the phagocytosis of effete epithelial cells. Intraepithelial lymphocytes possessing cytoplasmic granules, possibly intense in cytotoxicity, are topographically associated with the dying enterocytes, suggesting lymphocyte-mediated killing. After the engulfing of apoptotic enterocytes is left within the epithelium, maintaining the epithelial barrier until it is pinched off by the pushing of surrounding enterocytes. In the rat and mouse, on the other hand, effete enterocytes are exfoliated as a whole from the villus tips into the gut lumen. Macrophages, also numerous at the villus tips in these species, are less intense in phagocytotic activity. At the shoulder region of the villus, subepithelial macrophages extend thick processes deep into the epithelium; the processes appear to push out some enterocytes with typical apoptotic signs into the gut lumen. Lamina propria macrophages in the rat and mouse do not engulf enterocytes, but are believed to be involved in the induction of their apoptosis. The species difference in the mechanism of the apoptosis of enterocytes provides clues for understanding apoptosis.

Animals↗
PubMed1999

Effect of Salmonella typhimurium enterotoxin (S-LT) on lipid peroxidation and cell viability levels of isolated rat enterocytes.

Reactive oxygen species (ROS) are potent mediators of inflammatory disorders and may be of pathophysiological importance in S. typhimurium induced tissue damage. This study was carried out to investigate if ROS play a role in mediating the enterocyte damage during in vitro exposure to Salmonella typhimurium enterotoxin (S-LT). The ROS generation was detected by measuring the changes in the enterocyte arachidonic acid (AA) metabolism (measured indirectly by estimating the level of enterocyte damage in the absence and presence of the cyclooxygenase inhibitor, indomethacin) and xanthine oxidase activity. The enterocyte damage was estimated by measuring the changes in the level of lipid peroxidation and cell viability. The results obtained showed that the exposure of isolated rat enterocytes to S-LT resulted in an increased XO activity; an increased arachidonic acid metabolism, dose and time dependent increase in the level of lipid peroxidation and decreased cell viability. Lipid peroxidation decreased and cell viability increased in the presence of the antioxidant enzymes superoxide dismutase (SOD) or catalase. Thus the in vitro exposure of the enterocytes to S-LT is accompanied by an increased generation of ROS which may induce the lipid peroxidation of the enterocyte membrane thereby leading to a loss of cell viability.

Animals↗