Altered morphology in cultured rat intestinal epithelial IEC-6 cells is associated with alkaline phosphatase expression

Dietary lipid levels affected antioxidative status, inflammation response, apoptosis and microbial community in the intestine of juvenile turbot (Scophthalmus maximus L.)

A nine-week feeding trial was conducted to comprehensively investigate the effects of different levels of dietary lipid on intestinal physiology of juvenile turbot. Three diets with different lipid levels (8%, 12% and 16%) were formulated, which were designated as the low-lipid group (LL), medium-lipid group (ML) and high-lipid group (HL), respectively. Each diet was fed to six replicate tanks, and each tank was stocked with 35 fish. The results revealed that medium dietary lipid (12%) increased the activities of intestinal digestive enzymes and brush border enzymes. Excessive dietary lipid (16%) decreased the intestinal antioxidative enzyme levels and increased the lipid peroxidation pressure. In addition, HL stimulated the occurrence of intestinal inflammation and significantly up-regulated the mRNA expression level of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interferon-γ (IFN-γ) and transforming growth factor-β (TGF-β). Dietary LL and HL induced the apoptosis of intestinal epithelial cells. Sequencing of bacterial 16 s rRNA V4 region indicated that the abundance and diversity of intestinal microflora in fish fed with medium lipid diet (12%) were significantly higher than those in other groups, indicating the intestinal microflora ecology in group ML was more balanced. MetaStat analysis indicated that both low- and high-lipid diets significantly reduced the relative abundance of intestinal beneficial bacteria. In conclusion, results of this study demonstrated the sensitivity of intestinal health and microbiota to dietary lipid levels. From the perspective of microecological balance, medium dietary lipid (12%) was more conducive to maintaining the intestinal microflora stability of turbot.

Necrotizing Enterocolitis: Overview on In Vitro Models

Necrotizing enterocolitis (NEC) is a gut inflammatory disorder which constitutes one of the leading causes of morbidity and mortality for preterm infants. The pathophysiology of NEC is yet to be fully understood; several observational studies have led to the identification of multiple factors involved in the pathophysiology of the disease, including gut immaturity and dysbiosis of the intestinal microbiome. Given the complex interactions between microbiota, enterocytes, and immune cells, and the limited access to fetal human tissues for experimental studies, animal models have long been essential to describe NEC mechanisms. However, at present there is no animal model perfectly mimicking human NEC; furthermore, the disease mechanisms appear too complex to be studied in single-cell cultures. Thus, researchers have developed new approaches in which intestinal epithelial cells are exposed to a combination of environmental and microbial factors which can potentially trigger NEC. In addition, organoids have gained increasing attention as promising models for studying NEC development. Currently, several in vitro models have been proposed and have contributed to describe the disease in deeper detail. In this paper, we will provide an updated review of available in vitro models of NEC and an overview of current knowledge regarding its molecular underpinnings.

Cytotoxic Effects of the Dual ErbB Tyrosine Kinase Inhibitor, Lapatinib, on Walker 256 Rat Breast Tumour and IEC-6 Rat Normal Small Intestinal Cell Lines

Lapatinib is an orally administered, dual ErbB1/ErbB2 tyrosine kinase inhibitor (TKI). It is effective in ErbB2 + ve breast cancer treatment. However, lapatinib is associated with diarrhoea with an incidence of 47–75%. The mechanism of ErbB1 TKI-induced diarrhoea remains unclear. ErbB1 or epidermal growth factor receptor (EGFR) is expressed in gastrointestinal mucosa whereby the primary site for drug absorption is intestine. Thus, administration of ErbB1 oral TKI may disrupt gut homeostasis, leading to diarrhoea. Nevertheless, further investigations are required. We observed that lapatinib inhibited 50% Walker 256 breast tumour cells and IEC-6 small intestinal cell growth. Higher percentage of necrosis was observed in lapatinib-treated Walker 256. Lapatinib-treated IEC-6 showed higher percentage of late apoptosis. Only ErbB2 mRNA was detected in Walker 256 but both ErbB1 and ErbB2 mRNAs were detected in IEC-6, yet both protein staining were detected in both cells. Lapatinib exhibited cytotoxic properties on ErbB1/ErbB2 expressing cell lines, with intestinal cells being more sensitive to lapatinib compared to tumour cells. Lapatinib induced necrosis in tumour cells, while inducing late apoptosis in intestinal cells may explain lapatinib-induced diarrhoea in patients administered with the drug which could be due to apoptosis of intestinal epithelial cells leading to barrier disruption and consequently diarrhoea.

Effects of maize naturally contaminated with aflatoxin B1 on growth performance, intestinal morphology, and digestive physiology in ducks

This study was conducted to determine the effects of maize naturally contaminated with aflatoxin B1 (AFB1) on growth performance, intestinal morphology, relative digestive organs weight, digestive enzymes activities, and biochemical index of intestinal development in ducks. A total of 640 ducks was blocked on the basis of sex and body weight, and then allocated randomly to 2 treatments with 20 pens per treatment and 16 ducks per pen. The experiment lasted for 5 wk, and dietary treatments included basal diet (CON) and diets with 100% of normal maize replaced by AFB1 contaminated maize. Detectable levels of other toxins were present but only AFB1 exceeded limits and the level of AFB1 was 195.4 ug/kg in the contaminated maize, and ranged from 2.91 to 120.02 ug/kg in the starter diet and 2.03 to 153.12 ug/kg in the grower diet. Feeding AFB1 contaminated diets decreased (P < 0.05) ADG and ADFI during the whole experiment, whereas F/G during d 15 to 35 and d zero to 35 was reduced (P < 0.05). The mortality of ducks fed AFB1 contaminated diets increased (P < 0.05). Ducks fed AFB1 contaminated diets had greater (P < 0.05) relative weights of proventriculus and gizzard on d 14 as well as the duodenum, jejunum, and ileum on d 14 and 35. Feeding AFB1 contaminated diets increased (P < 0.05) crypt depth, villus width, and surface area in the duodenum on d 35 and villus height, villus width, and surface area in the jejunum on d 14. The activities of alkaline phosphatase and leucine aminopeptidase in the jejunum brush border together with chymotrypsin and trypsin in the pancreas increased (P < 0.05) on d 14 with the inclusion of AFB1 contaminated maize. The jejunum villus became long and wide in ducks fed AFB1 contaminated diets. Taken together, the feeding of maize naturally contaminated with AFB1 caused adverse effects on growth performance and intestinal morphology, and altered digestive physiology and development.

Stereochemistry as a determining factor for the effect of a cell-penetrating peptide on cellular viability and epithelial integrity

Cell-penetrating peptides (CPPs) comprise efficient peptide-based delivery vectors. Owing to the inherent poor enzymatic stability of peptides, CPPs displaying partial or full replacement of l-amino acids with the corresponding d-amino acids might possess advantages as delivery vectors. Thus, the present study aims to elucidate the membrane- and metabolism-associated effects of l-Penetratin (l-PEN) and its corresponding all-d analog (d-PEN). These effects were investigated when exerted on hepatocellular (HepG2) or intestinal (Caco-2 and IEC-6) cell culture models. The head-to-head comparison of these enantiomeric CPPs included evaluation of their effects on cell viability and morphology, epithelial membrane integrity, and cellular ultrastructure. In all investigated cell models, a rapid decrease in cell viability, pronounced membrane perturbation and an altered ultrastructure were detected upon exposure to d-PEN. At equimolar concentrations, these observations were less pronounced or even absent for cells exposed to l-PEN. Both CPPs remained stable for at least 2 h during exposure to proliferating cells (cultured for 24 h), although d-PEN exhibited a longer half-life when compared with that of l-PEN when exposed to well-differentiated cell monolayers (cultured for 18-20 days). Thus, the stereochemistry of the CPP penetratin significantly influences its effects on cell viability and epithelial integrity when profiled against a panel of mammalian cells.

Effects of dietary vitamin E on growth performance as well as intestinal structure and function of channel catfish (Ictalurus punctatus, Rafinesque 1818)

To evaluate the impact of dietary vitamin E supplementation on growth performance, the intestinal structure and function of channel catfish (Ictalurus punctatus, Rafinesque 1818) was investigated. A total of 900 healthy channel catfish (weight, 5.20±0.15 g) were divided into four groups, which received experimental diets with different vitamin E content (0, 50, 100 or 1,000 mg/kg). At the end of the feeding trial (after 15 weeks), the growth and gut performance of the animals was determined. The digestive enzyme activity in hepatopancreas and gut was also detected. In addition, the height of intestinal fold, the thickness of the mucous membrane and the number of somatostatin-positive cells was examined by histological analysis. Dietary vitamin E supplementation at 50 and 100 mg/kg significantly improved the growth and gut performance, which also increased the activity of several digestive enzymes compared to that in animals without vitamin E supplementation (P<0.05). In addition, vitamin E supplementation also significantly increased the height of intestinal fold and the thickness of the mucous membrane (P<0.05). Fish with dietary vitamin E supplementation at appropriate doses also had more somatostatin-positive cells in than those without vitamin E supplementation (P<0.05). In conclusion, dietary vitamin E supplementation at 50 and 100 mg/kg was shown to improve the growth performance as well as intestinal structure and function of channel catfish.

PAR2-dependent activation of GSK3β regulates the survival of colon stem/progenitor cells

Protease-activated receptors PAR1 and PAR2 play an important role in the control of epithelial cell proliferation and migration. However, the survival of normal and tumor intestinal stem/progenitor cells promoted by proinflammatory mediators may be critical in oncogenesis. The glycogen synthase kinase-3β (GSK3β) pathway is overactivated in colon cancer cells and promotes their survival and drug resistance. We thus aimed to determine PAR1 and PAR2 effects on normal and tumor intestinal stem/progenitor cells and whether they involved GSK3β. First, PAR1 and PAR2 were identified in colon stem/progenitor cells by immunofluorescence. In three-dimensional cultures of murine crypt units or single tumor Caco-2 cells, PAR2 activation decreased numbers and size of normal or cancerous spheroids, and PAR2-deficient spheroids showed increased proliferation, indicating that PAR2 represses proliferation. PAR2-stimulated normal cells were more resistant to stress (serum starvation or spheroid passaging), suggesting prosurvival effects of PAR2 Accordingly, active caspase-3 was strongly increased in PAR2-deficient normal spheroids. PAR2 but not PAR1 triggered GSK3β activation through serine-9 dephosphorylation in normal and tumor cells. The PAR2-triggered GSK3β activation implicates an arrestin/PP2A/GSK3β complex that is dependent on the Rho kinase activity. Loss of PAR2 was associated with high levels of GSK3β nonactive form, strengthening the role of PAR2 in GSK3β activation. GSK3 pharmacological inhibition impaired the survival of PAR2-stimulated spheroids and serum-starved cells. Altogether our data identify PAR2/GSK3β as a novel pathway that plays a critical role in the regulation of stem/progenitor cell survival and proliferation in normal colon crypts and colon cancer.

Elucidating pathways of Toxoplasma gondii invasion in the gastrointestinal tract: involvement of the tight junction protein occludin

Toxoplasma gondii is an obligate intracellular parasite infecting one third of the world's population. The small intestine is the parasite's primary route of infection, although the pathway of epithelium transmigration remains unclear. Using an in vitro invasion assay and live imaging we showed that T. gondii (RH) tachyzoites infect and transmigrate between adjacent intestinal epithelial cells in polarized monolayers without altering barrier integrity, despite eliciting the production of specific inflammatory mediators and chemokines. During invasion, T. gondii co-localized with occludin. Reducing the levels of endogenous cellular occludin with specific small interfering RNAs significantly reduced the ability of T. gondii to penetrate between and infect epithelial cells. Furthermore, an in vitro invasion and binding assays using recombinant occludin fragments established the capacity of the parasite to bind occludin and in particular to the extracellular loops of the protein. These findings provide evidence for occludin playing a role in the invasion of T. gondii in small intestinal epithelial cells.

Silencing the Menkes copper-transporting ATPase (Atp7a) gene in rat intestinal epithelial (IEC-6) cells increases iron flux via transcriptional induction of ferroportin 1 (Fpn1)

The Menkes copper-transporting ATPase (Atp7a) gene is induced in rat duodenum during iron deficiency, consistent with copper accumulation in the intestinal mucosa and liver. To test the hypothesis that ATP7A influences intestinal iron metabolism, the Atp7a gene was silenced in rat intestinal epithelial (IEC-6) cells using short hairpin RNA (shRNA) technology. Perturbations in intracellular copper homeostasis were noted in knockdown cells, consistent with the dual roles of ATP7A in pumping copper into the trans-Golgi (for cuproenzyme synthesis) and exporting copper from cells. Intracellular iron concentrations were unaffected by Atp7a knockdown. Unexpectedly, however, vectorial iron ((59)Fe) transport increased (∼33%) in knockdown cells grown in bicameral inserts and increased further (∼70%) by iron deprivation (compared with negative control shRNA-transfected cells). Additional experiments were designed to elucidate the molecular mechanism of increased transepithelial iron flux. Enhanced iron uptake by knockdown cells was associated with increased expression of a ferrireductase (duodenal cytochrome b) and activity of a cell-surface ferrireductase. Increased iron efflux from knockdown cells was likely mediated via transcriptional activation of the ferroportin 1 gene (by an unknown mechanism). Moreover, Atp7a knockdown significantly attenuated expression of an iron oxidase [hephaestin (HEPH); by ∼80%] and membrane ferroxidase activity (by ∼50%). Cytosolic ferroxidase activity, however, was retained in knockdown cells (75% of control cells), perhaps compensating for diminished HEPH activity. This investigation has thus documented alterations in iron homeostasis associated with Atp7a knockdown in enterocyte-like cells. Alterations in copper transport, trafficking, or distribution may underlie the increase in transepithelial iron flux noted when ATP7A activity is diminished.

Alkaline phosphatases contribute to uterine receptivity, implantation, decidualization, and defense against bacterial endotoxin in hamsters

Alkaline phosphatase (AP) activity has been demonstrated in the uterus of several species, but its importance in the uterus, in general and during pregnancy, is yet to be revealed. In this study, we focused on identifying AP isozyme types and their hormonal regulation, cell type, and event-specific expression and possible functions in the hamster uterus during the cycle and early pregnancy. Our RT-PCR and in situ hybridization studies demonstrated that among the known Akp2, Akp3, Akp5, and Akp6 murine AP isozyme genes, hamster uteri express only Akp2 and Akp6; both genes are co-expressed in luminal epithelial cells. Studies in cyclic and ovariectomized hamsters established that while progesterone (P₄) is the major uterine Akp2 inducer, both P₄ and estrogen are strong Akp6 regulators. Studies in preimplantation uteri showed induction of both genes and the activity of their encoded isozymes in luminal epithelial cells during uterine receptivity. However, at the beginning of implantation, Akp2 showed reduced expression in luminal epithelial cells surrounding the implanted embryo. By contrast, expression of Akp6 and its isozyme was maintained in luminal epithelial cells adjacent to, but not away from, the implanted embryo. Following implantation, stromal transformation to decidua was associated with induced expressions of only Akp2 and its isozyme. We next demonstrated that uterine APs dephosphorylate and detoxify endotoxin lipopolysaccharide at their sites of production and activity. Taken together, our findings suggest that uterine APs contribute to uterine receptivity, implantation, and decidualization in addition to their role in protection of the uterus and pregnancy against bacterial infection.

The effect of oxidative stress upon the intestinal epithelial uptake of butyrate

Our aim was to investigate the effect of oxidative stress upon butyrate uptake at the intestinal epithelial level. For this, IEC-6 cells were treated with tert-butylhydroperoxide 3000μM (tBOOH), which increased levels of oxidative stress biomarkers, while maintaining cellular viability. The effect of tBOOH upon uptake of [(14)C]butyrate ([(14)C]BT) (10μM) can be summarized as follows: (a) it caused a reduction in the intracellular accumulation of [(14)C]BT over time, (b) it strongly reduced total [(14)C]BT uptake but did not affect Na(+)-independent uptake of [(14)C]BT, and (c) it did not affect the kinetics of [(14)C]BT uptake at 37°C, but increased uptake at 4°C. Moreover, tBOOH increased the efflux of [(14)C]BT not mediated by breast cancer resistance protein. We thus conclude that tBOOH strongly inhibits Na(+)-coupled monocarboxylate cotransporter 1 (SMCT1)-mediated, but not H(+)-coupled monocarboxylate transporter (MCT1)-mediated butyrate uptake; moreover, it increases uptake and efflux of butyrate by passive diffusion. tBOOH did not affect the mRNA expression levels of MCT1 and SMCT1 nor their cell membrane insertion. Rather, its effect was dependent on extracellular signal regulated kinase 1/2 and protein tyrosine kinase activation and on the generation of reactive oxygen species by NADPH and xanthine oxidases and was partially prevented by the polyphenols quercetin and resveratrol. In conclusion, tBOOH is an effective inhibitor of SMCT1-mediated butyrate transport in non-tumoral intestinal epithelial cells. Given the important role played by butyrate in the intestine, this mechanism may contribute to the procarcinogenic and proinflammatory effect of oxidative stress at this level.

The effect of clotrimazole on energy substrate uptake and carcinogenesis in intestinal epithelial cells

Clotrimazole has anticarcinogenic activity in several cell types. Our aims were to investigate the anticarcinogenic effect of clotrimazole in a tumoral intestinal epithelial (Caco-2) cell line, to compare it with the effect in a nontumoral intestinal epithelial cell line (IEC-6 cells), and to investigate inhibition of energy substrate uptake as a mechanism contributing to it. The effect of clotrimazole on cell proliferation, viability and differentiation, H-deoxyglucose (H-DG), H-O-methyl-glucose (H-OMG), and C-butyrate uptake, as well as mRNA expression levels of glucose transporters was assessed. In Caco-2 cells, clotrimazole decreased cellular viability and proliferation and increased cell differentiation. The effect on cell proliferation and viability was potentiated by rhodamine123. Clotrimazole also decreased cellular viability and proliferation in IEC-6 cells, but increased the cellular DNA synthesis rate and had no effect on cell differentiation. Exposure of Caco-2 cells to clotrimazole (10 µmol/l) for 1 and 7 days increased (by 20-30%) the uptake of H-DG and H-OMG, respectively, but had no effect on C-butyrate uptake. The effect on H-DG and H-OMG transport was maximal at 10 µmol/l, and the pharmacological characteristics of transport were not changed. However, clotrimazole changed the mRNA expression levels of the facilitative glucose transporter 2 and the Na-dependent glucose cotransporter. Clotrimazole exhibits comparable cytotoxic effects in tumoral and nontumoral intestinal epithelial cell lines. In Caco-2 cells, the cytotoxic effect of clotrimazole was strongly potentiated by the inhibition of oxidative phosphorylation. Moreover, stimulation of glucose uptake might be a compensation mechanism in response to the glycolysis inhibition caused by clotrimazole.

Growth factor TGF-β induces intestinal epithelial cell (IEC-6) differentiation: miR-146b as a regulatory component in the negative feedback loop

TGF-β is a potent pleiotropic factor that promotes small intestinal cell differentiation. The role of microRNAs in the TGF-β induction of intestinal epithelial phenotype is largely unknown. We hypothesized that microRNAs are functionally involved in TGF-β-induced intestinal cell growth. In this study, TGF-β caused a morphological change of IEC-6 cells and stimulated expression of the epithelial cell markers alkaline phosphatase, villin, and aminopeptidase N. By global microRNA profiling during TGF-β-induced intestinal crypt cell (IEC-6) differentiation, we identified 19 differentially expressed microRNAs. We showed by real-time Q-PCR that miR-146b expression increased rapidly after TGF-β treatment; sequence analysis and in vitro assays revealed that miR-146b targets SIAH2, an E3 ubiquitin ligase, with decreased protein expression upon IEC-6 cell differentiation. Transfection of miR-146b inhibitor before TGF-β treatment blocked the down-regulation of SIAH2 in response to TGF-β. Moreover, SIAH2 over-expression during TGF-β treatment caused a significant decrease in Smad7 protein expression in IEC-6 cells. Furthermore, activation of the ERK1/2 pathway is active in the up-regulation of miR-146b by TGF-β. These findings suggest a novel mechanism whereby TGF-β signaling during IEC-6 cell differentiation may be modulated in part by microRNAs, and we propose a key role for miR-146b in the homeostasis of growth factor TGF-β signaling through a negative feedback regulation involving down-regulation of SIAH2 repressed Smad7 activities.

Effects of biodegradable Mg–6Zn alloy extracts on cell cycle of intestinal epithelial cells

In this study, intestinal epithelial cells (IEC)-6 were cultured in different concentration extracts of Mg–6Zn alloys for different time periods. We studied the indirect effects of Mg–6Zn alloys on cell cycle of IEC-6 cells. The cell cycle of IEC-6 cells was measured using flow cytometry. And, the cell cycle of IEC-6 cells was evaluated by investigating the expression of cyclin D1, CDK4, and P21 using real-time polymerase chain reaction (PCR) and Western blotting tests. It was found that the IEC-6 cells displayed better cell functions in 20% extract of the Mg–6Zn alloy extracts, compared to the 100% or 60% extract. The in vitro results indicated that the conspicuous alkaline environment that is a result of rapid corrosion of Mg–6Zn alloys is disadvantageous to cell cycle of IEC-6 cells.

Effects of dietary lipids and Clostridium butyricum on the performance and the digestive tract of broiler chickens

The effects of two sources of dietary lipids and supplementation of Clostridium butyricum on performance and intestinal metabolism of broilers were investigated. In a 2 x 2 factorial arrangement, 168 one-day-old broiler chicks were divided into four treatment groups, and fed four diets with two lipid sources (soya bean oil or fish oil, at 25 g/kg and 30 g/kg in starter and grower diets respectively), and without or with supplementation of C. butyricum (1 x 10(9) colony forming units per kg diet). C. butyricum had no effect on broiler performance. At 20 and 40 d of age, the pH of caecal digesta and the relative length of caecum were decreased after supplementation of C. butyricum (p < 0.05). After this treatment, the activity of alkaline phosphatase was increased in jejunal mucosa at 40 d of age (p < 0.01). Furthermore, there were increases in populations of lactic acid bacteria and the concentrations of acetic acid, n-butyric acid, n-valeric acid and total short chain fatty acids in caecal digesta of birds fed C. butyricum (p < 0.05). A significant interaction between lipid source and C. butyricum was found in the pH of caecal digesta at 20 d of age (p < 0.01). The results of the present study indicated that dietary supplementation of C. butyricum maybe a benefit for gut health of broiler chickens.

The short-chain fatty acid butyrate is a substrate of breast cancer resistance protein

Colorectal cancer is one of the most common cancers worldwide. Butyrate (BT) plays a key role in colonic epithelium homeostasis. The aim of this work was to investigate the possibility of BT being transported by P-glycoprotein (MDR1), multidrug resistance proteins (MRPs), or breast cancer resistance protein (BCRP). Uptake and efflux of (14)C-BT and (3)H-folic acid were measured in Caco-2, IEC-6, and MDA-MB-231 cell lines. mRNA expression of BCRP was detected by RT-PCR. Cell viability, proliferation, and differentiation were quantified with the lactate dehydrogenase, sulforhodamine B, and alkaline phosphatase activity assays, respectively. In both IEC-6 cells and Caco-2 cells, no evidence was found for the involvement of either MDR1 or MRPs in (14)C-BT efflux from the cells. In contrast, several lines of evidence support the conclusion that BT is a substrate of both rat and human BCRP. Indeed, BCRP inhibitors reduced (14)C-BT efflux in IEC-6 cells, both BT and BCRP inhibitors significantly decreased the efflux of the known BCRP substrate (3)H-folic acid in IEC-6 cells, and BCRP inhibitors reduced (14)C-BT efflux in the BCRP-expressing MDA-MB-231 cell line. In IEC-6 cells, combination of BT with a BCRP inhibitor significantly potentiated the effect of BT on cell proliferation. The results of this study, showing for the first time that BT is a BCRP substrate, are very important in the context of the high levels of BCRP expression in the human colon and the anticarcinogenic and anti-inflammatory role of BT at that level. So, interaction of BT with BCRP and with other BCRP substrates/inhibitors is clearly of major importance.

Active components of common traditional Chinese medicine decoctions have antioxidant functions

Many traditional Chinese medicine (TCM) decoctions are proven to have multiple functions in animal production. These decoctions are seldom recognized by the international scientific community because the mechanisms of action are not clearly elucidated. According to TCM theory, Cortex Phellodendri (COP), Rhizoma Atractylodes (RA), Agastache Rugosa (AR), and Gypsum Fibrosum (GF) can be used to formulate a medicinal compound that prevents or cures animal disease caused by heat stress. The aim of this research was to study the regulatory functions of the active components of TCM and to elucidate the effects of different TCM decoctions on antioxidant activity and lipid peroxide content, using in vitro and in vivo models of heat stress. For in vitro experiments, intestinal crypt-like epithelial cell line-6 (IEC-6) cells were employed to evaluate the effects of the active components of COP, RA, AR, and GF. For in vivo experiments, forty-eight 2-mo-old Chinese experimental mini-pigs (7.20 ± 0.02 kg) were randomly assigned to 4 groups: a normal-temperature group (NTG); a high-temperature group (HTG); HTG treated with COP, RA, AR, and GF (1:1:1:1, TCM1); and HTG treated with COP, RA, AR, and GF (1:1:1:0.5, TCM2). Results showed that the active components of the COP, RA, AR, and GF increased (P < 0.05) the proliferation and viability of heat-stressed IEC-6 cells and that the most effective treatment doses of COP alkaloid, RA Aetherolea, Herba Agastachis Aetherolea, and GF water extract were 200, 100, 100, and 200 µg/mL, respectively. All 4 active components increased (P < 0.05) superoxide dismutase, glutathione peroxidase activities, and glutathione content, and decreased (P < 0.05) malondialdehyde content with respect to the heat-stressed group to concentrations similar to those seen in NTG. In vivo experiments demonstrated that TCM1 and TCM2 improved (P < 0.05) the poor growth performance seen in HTG pigs. The superoxide dismutase, glutathione peroxidase activities, and malondialdehyde content in porcine jejunum treated with TCM1 and TCM2 were not different (P > 0.05) from those seen in the NTG and were better (P < 0.05) than results seen in the HTG. Overall, it appeared that TCM2 was more effective than TCM1 in ameliorating the effects of heat stress in pigs. In conclusion, this study revealed that the active components of common TCM decoctions have antioxidant functions.

Involvement of ERK1/2 signalling and growth-related molecules' expression in response to heat stress-induced damage in rat jejunum and IEC-6 cells

Our previous studies found small intestine epithelial tissues from several different animals (including rats, pigs and chickens) became significantly damaged following exposure to extreme heat. However, damaged tissue was rapidly repaired or regenerated in the following few days. Growth-related molecules are critical for cellular survival and promote endothelial cell proliferation and migration. The ERK1/2 signalling pathway is reported to regulate the growth and adaptation of endothelial cells to both physiological and pathological stimuli. However, little information is available concerning both growth-related molecules and ERK1/2 in response to heat stress. Herein, we employed both live rats and rat IEC-6 cells to investigate growth-related molecule expression and ERK1/2 activation in heat stress. Heat stress caused significant morphological damage to rat intestinal tissue and IEC-6 cells, reduced cell growth and proliferation, induced apoptosis, altered growth-related molecule mRNA expression and increased ERK1/2 phosphorylation. Addition of U0126 (a selective inhibitor of MEK kinase responsible for ERK phosphorylation) combined with heat stress exacerbated the morphological damage and apoptosis. With the addition of U0126, further up- or down-regulation of Egfr, Ctgf, Tgif, Vegfa, Okl38 and Gdf15 in response to heat stress was observed. In conclusion, extreme heat stress caused obvious damage to rat jejunum and IEC-6 cells. Both growth-related molecule expression and ERK1/2 phosphorylation were involved in response to heat stress. ERK1/2 inhibition exacerbated apoptosis and affected growth factor mRNA expression in heat stress.

Functional expression of double-stranded RNA-dependent protein kinase in rat intestinal epithelial cells

Intestinal epithelial cells (IECs) are exposed to external environment, microbial and viral products, and serve as essential barriers to antigens. Recent studies have shown that IECs express Toll-like receptors (TLRs) and respond to microbial components. The antimicrobial and antiviral barriers consist of many molecules including TLRs. To investigate the further component of this barrier in intestine, we examined the expression of double-stranded RNA-dependent protein kinase (PKR). PKR is a player in the cellular antiviral response and phosphorylates alpha-subunit of the eukaryotic translation initiation factor 2 (eIF-2alpha) to block protein synthesis and induces apoptosis. In this study, we showed that the expression of PKR was restricted to the cytoplasm of absorptive epithelial cells in the intestine of adult rat. We also demonstrated that PKR was expressed in the cultured rat intestinal epithelial cells (IEC-6). The level of PKR protein expression and the activity of alkaline phosphatase (ALP) increased in the cultured IEC-6 cells in a time-dependent manner. Inhibition of PKR by the 2-aminopurine treatment decreased ALP activity in the IEC-6 cells. Treatment of IEC-6 cells with synthetic double-stranded RNA (dsRNA) induced cell death in a dose-dependent manner. The addition of hydrocortisone also provoked suppression of PKR expression and ALP activity. This modulation might be mediated by signal transducers and activators of transcription-1 (STAT-1) protein. We concluded that PKR is expressed in IECs as potent barriers to antigens and is a possible modulator of the differentiation of rat IECs.

Functional cell models of the gut and their applications in food microbiology--a review

Animal experimentation has a long tradition for risk assessment of new drugs before they reach the clinic. To reduce expensive animal experimentation, attempts have been made to build inexpensive and convenient intestinal functional cell models to study toxicity and bioavailability of new substances along with providing relevant models to study interactions between the host, pathogens and intestinal microflora. We review the available cell lines and models of the intestine and their potential uses. Tumor derived cell lines such as Caco-2, T84 and HT-29 are widely used despite many drawbacks, which are discussed with respect to complexity of the gut, where various cell types interact with commensal microbiota and gut-associated lymphoid tissue. To address this complexity, 3D models of human and animal gut represent a promising in vitro system to mimic in vivo situation without the use of transformed cell lines.

Constitutive expression of IL-18 and IL-18R in differentiated IEC-6 cells: effect of TNF-alpha and IFN-gamma treatment

The multifunctional cytokine interleukin-18 (IL-18) is an important mediator in intestinal inflammatory processes. The aim of this study was to evaluate the constitutive expression of IL-18 and its receptors (IL-18Ralpha and IL-18Rbeta) in intestinal epithelial cells (IEC) stimulated by tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma). In addition, cellular proliferation and evaluation of brush border enzymes as differentiation markers were studied. Nontransformed rat intestinal epithelial IEC-6 cells were grown on an extracellular matrix (ECM) in medium with or without TNF-alpha, IFN-gamma, or a combination of both. Gene expression of IL-18, its receptors and apoptotic markers was evaluated using real-time PCR. Expression of IL-18Ralpha protein was demonstrated by flow cytometry and Western blot. Enzymatic activities of brush border enzymes and caspase-1 were determined. The constitutive expression of IL-18, IL-18Ralpha and IL-18Rbeta mRNAs and proteins were detected in IEC-6 cells. The biologically active form of IL-18 was released in response to TNF-alpha and IFN-gamma treatment. Exogenous IL-18 had no effect on cellular proliferation, brush border enzyme activities, and gene expression of apoptotic markers. However, the addition of IL-18 stimulated production and release of the chemokine IL-8. These data suggest that IEC-6 cells may be not only a source of IL-18 but also a target for its action.

Exogenous nucleosides modulate proliferation of rat intestinal epithelial IEC-6 cells

Exogenous nucleotides are considered semiessential nutritional components that play an important role in intestinal development, maintenance, and recovery from tissue damage. Nucleosides (NS) are the best-absorbed chemical form of nucleotides in the intestinal epithelium. The aim of this work was to clarify, at the cellular level, the effects described in vivo. Under conditions of high intracellular availability of NS, we studied the effects of 2 NS mixtures on the NS uptake and intracellular distribution and on the proliferation, morphology, viability, and cell-cycle phase distribution of rat intestinal epithelial cell line 6. Purine and pyrimidine NS showed a similar uptake profile, but the intracellular incorporation of guanosine was greater than that of uridine, without differences in intracellular distribution. Proliferation assays demonstrated that IEC-6 cell proliferation is increased by a mixture containing thymidine but decreased by one containing uridine. In fact, the antiproliferative effect started at 75 micromol/L, which indicated that it may not be correct to consider concentrations of uridine >75 micromol/L as physiological. Interestingly, these effects were not related to increased cell necrosis or apoptosis or to changed cell morphology but rather to a reduced S-phase and increased G0/G1 phase of the cell cycle. In summary, our results suggest that NS molecules are well-absorbed by rat intestinal epithelial cell line 6 cells, whose proliferation can be promoted or inhibited (according to the NS mixtures used) by a mechanism that is not dependent on the toxicity of the mixtures.

(2α,3β)-2,3-Dihydroxyolean-12-en-28-oic acid, a new natural triterpene fromOlea europea, induces caspase dependent apoptosis selectively in colon adenocarcinoma cells

Triterpenoids are known to induce apoptosis and to be anti-tumoural. Maslinic acid, a pentacyclic triterpene, is present in high concentrations in olive pomace. This study examines the response of HT29 and Caco-2 colon-cancer cell lines to maslinic-acid treatment. At concentrations inhibiting cell growth by 50-80% (IC50HT29=61+/-1 microM, IC80HT29=76+/-1 microM and IC50Caco-2=85+/-5 microM, IC80Caco-2=116+/-5 microM), maslinic acid induced strong G0/G1 cell-cycle arrest and DNA fragmentation, and increased caspase-3 activity. However, maslinic acid did not alter the cell cycle or induce apoptosis in the non-tumoural intestine cell lines IEC-6 and IEC-18. Moreover, maslinic acid induced cell differentiation in colon adenocarcinoma cells. These findings support a role for maslinic acid as a tumour suppressant and as a possible new therapeutic tool for aberrant cell proliferation in the colon. In this report, we demonstrate for the first time that, in tumoural cancer cells, maslinic acid exerts a significant anti-proliferation effect by inducing an apoptotic process characterized by caspase-3 activation by a p53-independent mechanism, which occurs via mitochondrial disturbances and cytochrome c release.

Surface modification and initial adhesion events for intestinal epithelial cells

Rapid resealing of the mucosal epithelia is imperative following injuries to the small intestine because the mucosa is responsible for the adsorption of nutrients as well as providing a barrier to noxious agents present in the lumen. Tissue engineering may provide a possible solution for treating intestinal erosions, ulcerations, inflammatory bowel disease, and infection. Cell-biomaterial interaction is a critical component in tissue engineering that can determine the success of the tissue construct. Cell-biomaterial interactions can be enhanced by various types of surface modification, which promote integrin ligation leading to increased cell function. In order to relate the effect of surface adhesion molecules to signaling events and macroscopic cell response, an intestinal epithelial cell line, IEC-6, was plated on fibronectin (receptor-mediated) and poly-L-lysine (non-specific) surfaces. Focal adhesion kinase (FAK) phosphorylation, cell spreading, and cell adhesion strength were measured. Results showed increases in FAK phosphorylation generally corresponded to increases in cell spreading and adhesion strength for IEC-6 cells. Therefore, in a simplified system, initial adhesion and signaling mechanisms appeared to correspond to subsequent physical responses in IEC-6 cells relevant to tissue engineering applications.

Modified vaccinia virus Ankara multiplies in rat IEC-6 cells and limited production of mature virions occurs in other mammalian cell lines

Recombinant viruses based on modified vaccinia virus Ankara (MVA) are vaccine candidates against infectious diseases and cancers. Presently, multiplication of MVA has been demonstrated in chicken embryo fibroblast and baby hamster kidney (BHK-21) cells only. The multiplication and morphogenesis of a recombinant (MVA-HANP) and non-recombinant MVA strain in BHK-21 and 12 other mammalian cell lines have now been compared. Rat IEC-6 cells were fully permissive to MVA infection. The virus yield in IEC-6 cells was similar to that obtained in BHK-21 cells at low as well as high multiplicities of infection. Vero cells were semi-permissive to MVA infection. Mature virions were produced in supposedly non-permissive cell lines. The multiplication and morphogenesis of non-recombinant MVA and MVA-HANP were similar. These results are relevant to the production and biosafety of MVA-vectored vaccines.

Cloning and expression of mouse peroxiredoxin I in IEC-6 Cells

AIM: To clone and express mouse peroxiredoxin I in IEC-6 cells.

METHODS: Total RNAs were isolated from cultured IEC-6 cells, and the coding region of peroxiredoxin I was amplified by RT-PCR. After it was cloned into T-vector and sequenced, pSG5 was used to transiently express peroxiredoxin I in IEC-6 by liposome-mediated transfection, and the expression of peroxiredoxin I was evaluated by RT-PCR and Western blot.

RESULTS: A DNA fragment about 750 bp was amplified from total RNAs of IEC-6 cells using specific primers of peroxiredoxin I. The sequencing confirmed the coding region was successfully cloned into T-vector, which was completely coincident with the sequence in GeneBank. After the EcoR I-BamH I fragment of T-vector containing peroxiredoxin I was inserted into pSG5, the recombinant plasmid was transferred to IEC-6 cells. RT-PCR assay showed that a DNA fragment of 930 bp could be amplified, which indicated the transcription of pSG5-Prx. Western blot confirmed the expression of peroxiredoxin I in IEC-6 cells.

CONCLUSION: Mouse peroxiredoxin I can be successfully expressed in IEC-6 cells.

Effect of gastrin on differentiation of rat intestinal epithelial cells in vitro

AIM: To investigate the effect of gastrin on differentiation of IEC-6 cell line in vitro.

METHODS: IEC-6 cells were incubated with gastrin. On day 7 after treatment, cell morphology was examined by light microscope, and on day 20, the cellular ultrastructures were examined by electron microscope. After exposure to gastrin for 6 hours, villin mRNA was analyzed by reverse transcription-polymerase chain reaction, and on day 7, the expression of villin was examined by immunocytochemical analysis with laser confocal microscope.

RESULTS: After exposure to gastrin, IEC-6 cells showed differentiated phenotypes as villas enterocytes and contained an abundance of plasma, small nuclei with nucleoli, and were arranged regularly. There were numerous microvilli around edge of the cells, and several cells showed columnar structures. Villin mRNA expression in cytoplasm was increased in comparison with control.

CONCLUSION: Differentiated characteristics of villus enterocytes and phenotypic changes of rat intestinal epithelial cells (IEC-6) are induced by gastrin, and the effects of gastrin are correlated to increased villin expression.