Transepithelial transport of putrescine across monolayers of the human intestinal epithelial cell line, Caco-2

AIM: To study the transepithelial transport characteristics of the polyamine putrescine in human intestinal Caco-2 cell monolayers to elucidate the mechanisms of the putrescine intestinal absorption. METHODS: The transepithelial transport and the cellular accumulation of putrescine was measured using Caco-2 cell monolayers grown on permeable filters. RESULTS: Transepithelial transport of putrescine in physiological concentrations (> 0.5 mM) from the apical to basolateral side was linear. Intracellular accumulation of putrescine was higher in confluent than in fully differentiated Caco-2 cells, but still negligible (less than 0.5%) of the overall transport across the monolayers in apical to basolateral direction.EGF enhanced putrescine accumulation in Caco-2 cells by four fold, as well as putrescine conversion to spermidine and spermine by enhancing the activity of S adenosylmethionine decarboxylase. However, EGF did not have any significant influence on putrescine flux across the Caco-2 cell monolayers. Excretion of putrescine from Caco-2 cells into the basolateral medium did not exceed 50 picomoles, while putrescine passive flux from the apical to the basolateral chamber, contributed hundreds of micromoles polyamines to the basolateral chamber. CONCLUSION :Transepithelial transport of putrescine across Caco2 cell monolayers occurs in passive diffusion, and is not influenced when epithelial cells are stimulated to proliferate by a potent mitogen such as EGF.     

Characterization of the human colon carcinoma cell line (Caco-2) as a model system for intestinal epithelial permeability

Caco-2 cells develop morphologic characteristics of normal enterocytes when grown on plastic dishes or nitrocellulose filters. The purpose of this study was to determine whether Caco-2 cells undergo similar differentiation when grown on Transwell polycarbonate membranes, and to study the suitability of Caco-2 monolayers as an intestinal epithelial transport model system. Transepithelial electrical resistance values after confluence were 173.5 omega.cm2 and remained unchanged through day 17. Permeabilities to the water-soluble fluid-phase markers that do not permeate the membrane, Lucifer yellow CH, [14C]inulin, [14C]polyethylene glycol, and [3H] dextran were less than 0.25% of the administered amount per hour after day 10. Qualitative evaluation of uptake and permeability to horseradish peroxidase confirmed the similarity in uptake and barrier properties between this cell system and the small intestinal epithelial layer. We conclude that Caco-2 cells grown on collagen-coated polycarbonate membranes should represent a valuable transport model system for the small intestinal epithelium.     

Salmonella interactions with polarized human intestinal Caco-2 epithelial cells

Polarized monolayers of the human intestinal epithelial Caco-2 cell line were grown on permeable filters and infected apically with either Salmonella choleraesuis or Salmonella typhimurium. Both Salmonella species penetrated through the monolayer, requiring 2 h before appearing in the basolateral medium. Both species caused a loss in transepithelial resistance by 3-4 h, and the monolayer's integrity was completely disrupted by 6 h. Scanning and transmission electron microscopy revealed that the bacteria interacted with well-defined apical microvilli and caused disruptions in the brush border, including elongation and denuding of the microvilli. The cytoplasm was also disrupted locally, with blebs protruding from the apical surface. The bacteria entered (invaded) these cells and were enclosed in membrane-bound vacuoles within the cytoplasm. By 6 h there were many bacteria within most Caco-2 cells, and these organisms caused serious cytopathic consequences. These morphologic observations correlated well with animal infection models, indicating that this in vitro system will be useful to study pathogens that interact with human intestinal epithelia.     

左旋肉碱对氧化应激损伤肾小管上皮细胞的保护作用

目的观察左旋肉碱对过氧化氢（H2O2）应激损伤人肾小管上皮细胞的保护作用,并探讨其可能机制。方法用H2O2作用于人肾小管上皮细胞系HK-2,建立肾小管上皮细胞氧化应激损伤模型;MTT法检测左旋肉碱预处理后HK-2细胞的活力;用酶化学法测定HK-2细胞超氧化物歧化酶（SOD）、谷胱甘肽过氧化物酶（GSH—Px）、过氧化氢酶（CAT）活性及总抗氧化能力（T—AOC）、丙二醛（MDA）;荧光显微镜观察及流式细胞仪测定细胞内活性氧（ROS）及HK-2细胞凋亡率。结果左旋肉碱预处理12h能抑制H2O2损伤所导致的HK-2细胞活力降低,增加细胞中SOD、GSH—Px和CAT含量,提高细胞T-AOC,降低细胞中MDA和ROS水平,抑制HK-2细胞凋亡。结论左旋肉碱对氧化应激所致的肾小管上皮细胞损伤具有保护作用,其机制可能与增强细胞抗氧化能力、减少自由基生成、抑制脂质过氧化反应及细胞凋亡有关。     

Phenolic and tyrosyl ring iodothyronine deiodination by the Caco-2 human colon carcinoma cell line

Thyroid hormone metabolism was studied in the human Caco-2 colon carcinoma cell line, which at confluence exhibits several functions of differentiated enterocytes. Cells were harvested two to 17 days after reaching confluence. Intact cells and homogenates were tested for deiodination of [125I]-labeled substrates. Small amounts of thyroxine (T4) were converted by homogenates to 3,3',5'-triiodothyronine (rT3), 3,3'-diiodothyronine (3,3'-T2), and 1-, with no detectable production of 3,5,3'-triiodothyronine (T3) by homogenates or cells. rT3 was converted to 3,3'-T2 and 1- with an apparent Michaelis constant (Km) for rT3 of 24 nmol/L; 6-n-propyl-2-thiouracil (PTU) had a 50% inhibitory concentration of 30 nmol/L and abolished rT3 5'-deiodination at 1 mmol/L in the presence of 20 mmol/L dithiothreitol (DTT). T3 was deiodinated to 3,3'-T2 and 3'-monoiodothyronine (3'-T1) with an apparent Michaelis constant (Km) for T3 of 5.7 nmol/L; this reaction was not inhibited by 1 mmol/L PTU. Phenolic and tyrosyl ring deiodinating activities were maximal four and six days, respectively, after the cells reached confluence. Homogenates of cells grown in standard medium containing fetal calf serum had fivefold higher rT3 5'-deiodinating activity than cells grown in a serum-free defined culture medium, reflecting a fivefold difference in the apparent Vmax with no difference in the apparent Km for rT3. There was no difference in T3 5-deiodination rates in homogenates of Caco-2 cells grown in the two media until 12 days postconfluence, when cells grown in standard medium had higher activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

高氧对肠上皮细胞表达分泌片的影响

目的:研究高氧对肠上皮细胞分泌片(SC)表达的影响.方法:采用细胞计数和Giemsa染色方法检测不同氧浓度对细胞生长和细胞分裂能力的影响,采用免疫组织化学方法检测不同氧浓度对Caco-2表达SC的影响.结果:细胞计数显示400mL/L氧浓度利于细胞生长;600、900mL/L氧浓度导致细胞迅速死亡.不同氧浓度干预细胞3d细胞分裂指数有明显不同,分裂细胞百分数分别为正常氧浓度2.5;400mL/L氧浓度为3.3;600mL/L氧浓度为1.3;900mL/L氧浓度大部分细胞死亡.与正常氧浓度相比,氧浓度为400、600mL/L时SC表达增强,900mL/L氧浓度时SC表达明显减弱,甚为阴性,但600mL/L氧浓度SC表达较400mL/L氧浓度减弱.结论:适度的高氧促进细胞生长和促进肠上皮细胞表达SC,严重高氧则抑制肠上皮细胞SC表达及肠上皮细胞生长,肠上皮细胞SC表达增多有助于保护肠黏膜及平衡肠黏膜作用,阻滞细菌入侵肠道.     

Cdx1 promotes differentiation in a rat intestinal epithelial cell line

BACKGROUND & AIMS: Homeobox genes are involved in establishing and maintaining differentiated patterns in adult tissues. Cdx1 might carry out that function in the intestinal epithelium because its expression is specific to that tissue and increases during development. METHODS: Cdx1 expression was induced in IEC-6 intestinal epithelial cells by stable transfection, and subsequent changes in cell growth, resistance to apoptosis, migration, and differentiation were monitored. RESULTS: Compared with control, IEC-6/Cdx1 cells proliferated more rapidly, were more resistant to apoptosis, and migrated 3-4 times faster, as shown by an in vitro wound assay. IEC-6/Cdx1 cells in culture formed multilayers. Morphology of the top layer was similar to that of columnar epithelium, with cells showing typical features of differentiated enterocytes, including complex junctions and well-developed microvilli with glycocalix. Expression of 2 markers of enterocyte differentiation, aminopeptidase N and villin, was induced in IEC-6/Cdx1 cells. Aminopeptidase N was targeted to the basolateral membrane, and villin was localized to the cytoplasm. Actin filaments, which were mostly present in transcytoplasmic stress fibers in control cells, were redistributed to the cortex in Cdx1-transfected cells. CONCLUSIONS: Cdx1 expression in IEC-6 cells induces phenotypic changes characteristic of differentiating enterocytes, suggesting an important role for Cdx1 in the transition from stem cells to proliferating/transit cells.     

Protection of gastric epithelial cell monolayers from a human cell line by omeprazole in vitro

Omeprazole has an anti-ulcerogenic effect and protects rat gastric mucosa against drug-induced damage in vivo. We have evaluated omeprazole protection against damage induced by sodium taurocholate to gastric epithelial cell monolayers, an experimental model that completely excludes the influence of systemic factors. Furthermore, since our model consists of mucus-producing cells, the acid inhibitory effect of the drug in any protection is negligible. The role of prostaglandin and sulfhydryls in any such protection has also been evaluated. Monolayers of gastric cells from a well-differentiated human cell line were studied. A chromium-51 release assay was used to assess cell damage. Sodium taurocholate damaged cells dose-dependently (r = 0.97, p less than 0.01). Pretreatment with omeprazole significantly reduced the amount of cell damage brought about by sodium taurocholate (p less than 0.001). Indomethacin did not prevent the protection afforded by omeprazole, nor did incubation with omeprazole increase the amount of prostaglandin E2 produced by cultured cells. Omeprazole did not increase the amount of sulfhydryl compounds in cultured cells. These results indicate that omeprazole protects gastric cells independently of systemic factors and of inhibition of gastric acid secretion. This protection is not related to stimulation of prostaglandin synthesis nor is it associated with an increase of endogenous sulfhydryl compounds.     

EGF-stimulated polyamine accumulation in the colon carcinoma cell line, Caco-2

BACKGROUND: Polyamines (putrescine, spermidine and spermine) are ubiquitous molecules indispensable for cell proliferation. In the intestinal lumen they are present in high amounts. Polyamine accumulation in proliferating cells of the intestinal mucosa is high, and it occurs both by enhanced synthesis and by increased uptake from the lumen. AIMS: To study mitogen-induced polyamine accumulation in the gut, we treated proliferating Caco-2 cells with epidermal growth factor (EGF) and measured the activity of ornithine decarboxylase (ODC) and putrescine uptake. Furthermore, we investigated whether EGF-induced changes in the apical membrane could be responsible for the effect of EGF on polyamine uptake in Caco-2 cells. METHODS: Putrescine uptake, ODC activity and intracellular polyamine content were evaluated in the presence of 100 ng/ml EGF. To study the mechanisms of EGF-stimulated polyamine uptake, apical membrane vesicles were isolated, and putrescine uptake into the vesicles measured. Possible enrichment in brush border membrane cytoskeleton proteins (ezrin and villin) was assessed by Western blot. RESULTS: Treatment with EGF induced an increase in ODC activity, which occurred within the first minutes of treatment and reached peak values after 3 h. In contrast, an increase in putrescine uptake was more sustained, with peak levels at 12 h. Both synthesis and uptake contributed to an over 60% increase in intracellular putrescine and spermidine after EGF treatment. There were no detectable changes in apical membrane cytoskeleton (as concluded by the absence of ezrin and villin enrichment in EGF-treated Caco-2 cells). However, in apical membrane vesicles isolated from EGF-pretreated cells, putrescine uptake was enhanced twofold. CONCLUSIONS: EGF stimulates both synthesis and uptake of polyamines in Caco-2 cells. Enhanced synthesis seems to ensure rapid supply with polyamines in the earliest stages of growth, while the uptake is responsible for the maintenance of high polyamine intracellular levels during late growth phases. EGF-stimulated polyamine uptake is apparently not a consequence of structural changes in the apical membrane, but is likely to occur by a distinct EGF-induced alteration of the polyamine transporter itself.     

Superoxide: a major factor for stress protein induction in reoxygenation injury in the intestinal cell line Caco-2.

BACKGROUND/AIMS: Acute intestinal ischemia is followed by cellular destruction and loss of mucosal barrier function. Posthypoxic injury of cellular proteins leads to the synthesis of heat shock proteins. The role of oxygen radicals in this process, however, is not fully established. METHODS: In the present study, using the intestinal cell line Caco-2, we investigated the relationship between the synthesis of the heat shock protein HSP70, detected by Western blot and oxygen radicals as well as lactate dehydrogenase (LDH) release, as measured in photometrical tests. RESULTS: Various periods of hypoxia and 30 min of reoxygenation resulted in an increased generation of superoxide as measured by the tetrazolium base 3-(4, 5-dimethylthiazol-2-yl)2,5-diphenyltetrazoliumbromide. The inhibitor of superoxide dismutase (SOD), diethyldithiocarbamate (DDC) increased and addition of SOD decreased intracellular superoxide levels. HSP70 synthesis was detectable after 2 h of hypoxia. Similar to superoxide production, DDC increased and SOD reduced the HSP70 synthesis. In contrast, the increased LDH release from the cells observed after hypoxia was not significantly altered by DDC and SOD. CONCLUSION: The production of superoxide correlates with HSP70 induction, but not with LDH release. We conclude that hypoxia/reoxygenation induces heat shock protein production, a result of protein damage, by increased superoxide generation, whereas superoxide does not correlate with membrane damage in Caco-2 cells.     

Effects of metformin on bile salt transport by monolayers of human intestinal Caco-2 cells

The antidiabetic biguanide metformin has been shown to increase faecal excretion of bile salts in type 2 diabetes. Cultured human intestinal Caco-2 cell monolayers provide a model of human enterocytes. These monolayers are used here to determine the effect of metformin on the secondary-active, sodium-linked transfer of ¹⁴C-glycocholate from the apical (brush border) to the basolateral (serosal) surface. During 24-h incubations, 10⁻² mol/l metformin significantly reduced ¹⁴C-glycocholate transfer. This could not be attributed to alterations of monolayer integrity or Na⁺-K⁺ ATPase pump activity. For example, the secondary-active transport of glucose and proline was not interrupted, and the inhibitory effect of metformin on bile salt transport was additive to the inhibitory effect of ouabain. The results suggest that metformin can act directly on intestinal enterocytes to reduce the active transfer of bile salts by a mechanism that is independent of Na⁺-K⁺ ATPase activity.     

Evidence that PGE2 stimulates intestinal epithelial cell adenylate cyclase by a receptor-mediated mechanism

These studies were performed to examine whether prostaglandin E₂ stimulates intestinal epithelial secretion via a receptor-mediated or non-receptor-mediated activation of adenylate cyclase. Solubilization of epithelial cell adenylate cyclase with Lubrol PX, which separates the receptor moiety of the cyclase from the remainder of the complex, inhibited the prostaglandin E₂ stimulation of the cyclase. A similar result was obtained with VIP, which activates adenylate cyclase via a receptor-mediated mechanism, whereas fluoride, S-GTP, and forskolin, which activate the cyclase via non-receptor-mediated mechanisms, all stimulated solubilized adenylate cyclase. In addition, prostaglandin E₂ and VIP both showed a dependence on GTP for adenylate cyclase stimulation while fluoride and forskolin did not. These data suggest that prostaglandin E₂ activates intestinal mucosal adenylate cyclase by a receptor-mediated mechanism. The presence of such receptors lends support to the possibility that prostaglandins have a physiological role in the control of mucosal transport.     

Growth inhibition and differentiation of the human colon carcinoma cell line, Caco-2, by constitutive expression of insulin-like growth factor binding protein-3

The human colon carcinoma cell line, Caco-2, produces insulin-like growth factor binding protein-3 (IGFBP-3), the secretion of which correlates with markers of enterocyte differentiation. To investigate whether IGFBP-3 inhibits proliferation or induces differentiation, Caco-2 cells were stably transfected with an IGFBP-3 cDNA expression construct or pcDNA3 vector as a control. Accumulation of IGFBP-3 mRNA and secretion of the protein into conditioned medium 9 days after plating were readily detected in the transfected cells, whereas these parameters were undetectable in pcDNA3-transfected cells. Insulin-like growth factor binding protein-3-expressing cells grew at a rate similar to the controls for 6 days after plating, but achieved a much lower final density between days 10 and 12. By day 9 of culture, accumulation of sucrase-isomaltase mRNA, a marker of enterocytic differentiation of Caco-2 cells, was evident in the IGFBP-3-expressing cells, but was undetectable in the controls. These results indicate that IGFBP-3 may inhibit proliferation and induce early differentiation of Caco-2 cells.     

Pseudomonas fluorescens alters epithelial permeability and translocates across Caco-2/TC7 intestinal cells

Background

Pseudomonas fluorescens has long been considered as a psychrotrophic microorganism. Recently, we have shown that clinical strains of P. fluorescens (biovar 1) are able to adapt at a growth temperature of 37°C or above and induce a specific inflammatory response. Interestingly, a highly specific antigen of P. fluorescens, I2, is detected in the serum of patients with Crohn's disease but the possible role of this bacterium in the disease has not yet been explored. In the present study, we examined the ability of a psychrotrophic and a clinical strain of P. fluorescens to modulate the permeability of a Caco-2/TC7 intestinal epithelial model, reorganize the actin cytoskeleton, invade the target cells and translocate across the epithelium. The behaviour of these two strains was compared to that of the well known opportunistic pathogen P. aeruginosa PAO1.

Results

Both strains of P. fluorescens were found to decrease the transepithelial resistance (TER) of Caco-2/TC7 differentiated monolayers. This was associated with an increase in paracellular permeability and F-actin microfilaments rearrangements. Moreover, the invasion and translocation tests demonstrated that the two strains used in this study can invade and translocate across the differentiated Caco-2/TC7 cell monolayers.

Conclusions

The present work shows for the first time, that P. fluorescens is able to alter the intestinal epithelial barrier function by disorganizing the F-actin microfilament network. Moreover, we reveal that independently of their origins, the two P. fluorescens strains can translocate across differentiated Caco-2/TC7 cell monolayers by using the transcellular pathway. These findings could, at least in part, explain the presence of the P. fluorescens specific I2 antigen in the serum of patients with Crohn's disease.