Supernatants of HIV-infected immune cells affect the barrier function of human HT-29/B6 intestinal epithelial cells

OBJECTIVES: Characterization of the diarrhoea-inducing effect of altered cytokine production in HIV infection. METHODS: Monocyte-derived macrophages (MDM) were infected with macrophagetropic (SF162) and lymphocytotropic (IIIB) HIV-1 strains and cocultured with autologous peripheral blood mononuclear cells (PBMC). After 24 h the supernatants were collected and tested for their immunoreactive levels of cytokines by enzyme-linked immunosorbent assay. The effects of the supernatants and the respective recombinant human cytokines on barrier function of HT-29/B6 cells were determined. RESULTS: Infection of MDM with HIV-1 SF162 or IIIB led to increased production of tumour necrosis factor-alpha (TNFalpha), interleukin-1-beta, interferon-alpha and interferon-gamma after cell-cell contact with PBMC. Supernatants of infected cells decreased transepithelial resistance (R(t)), with higher effects on R(t) in HIV IIIB infection, which was due to higher cytokine concentrations. The effect was not due to cytotoxicity (negative LDH assay) or epithelial monolayer disruption [zonula occludens protein-1 (ZO-1) immunofluorescence staining]. The effect of HIV-1 IIIB coculture supernatants could be mimicked by the respective recombinant human cytokines. TNFalpha is an effector cytokine, because inhibition of TNFalpha by its soluble receptor decreased the effect of the supernatants on transepithelial resistance. Conductance scanning indicated the cytokine-induced barrier defect to be due to both, induction of epithelial apoptoses and tight junction alterations. CONCLUSIONS: Cell-cell interaction of HIV-infected macrophages with PBMC leads to a release of cytokines sufficient to alter intestinal epithelial barrier function. The main effect was mediated by TNFalpha inducing a leak-flux which may contribute to the diarrhoea by HIV per se (HIV-enteropathy).     

Proinflammatory effects and molecular mechanisms of interleukin-17 in intestinal epithelial cell line HT-29

AIM: To evaluate the proinflammatory effects and molecular mechanisms of interleukin (IL)-17 in intestinal epithelial cell line HT-29.METHODS: HT-29 cells were cultured with IL-17, tumor necrosis factor (TNF)-α, or the combination of both IL-17 and TNF-α. Real-time PCR and Western blot were used to measure the gene expression levels of neutrophil chemokines CXCL1, CXCL2, CXCL5, CXCL6, IL-8 and TH-17 cell chemokine CCL20, the phosphorylation levels of p38 and TNF-α, and the expression level of IL-8, after using the p38 inhibitor in HT-29 cells. The stable Act1 knockdown HT-29 cell line was established to further test the phosphorylation changes of p38, after using IL-17 and TNF-α.RESULTS: After HT-29 cells were cultured with IL-17 and TNF-α, the expression levels of neutrophil chemokines (CXCL1, CXCL2, CXCL5, CXCL6, IL-8) and Th17 chemokine (CCL20) significantly improved (24.96 ± 2.53, 28.47 ± 2.87, 38.08 ± 2.72, 33.47 ± 2.41, 31.7 ± 2.38, 44.37 ± 2.73, respectively), and the differences were all statistically significant (P < 0.01). Western blot results showed that IL-17 obviously enhanced the phosphorylation level of p38, which was induced by TNF-α. Compared with the control group, the expression level of IL-8 significantly declined (9.47 ± 1.36 vs 3.06 ± 0.67, P < 0.01) when TH-29 cells were cultured with IL-17 and TNF-α. p38 inhibition assay showed that the p38 pathway played an essential role in the inflammatory response induced by IL-17. p38 phosphorylation levels could not be changed after using IL-17 and TNF-α in the stable Act1 knockdown HT-29 cell line.CONCLUSION: IL-17 significantly promoted the gene expression levels of TNF-α-induced neutrophil chemokines and Th17 cell chemokine. It is obvious that IL-17 and TNF-α have synergistic effects on p38.     

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.     

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.     

Transcobalamin codon 259 polymorphism in HT-29 and Caco-2 cells and in Caucasians: relation to transcobalamin and homocysteine concentration in blood

Transcobalamin (TC) is the plasma transporter that delivers vitamin B(12) to cells. We have already reported that HT-29 and Caco-2 cells secrete different TC variants. HT-29 secretes 2 TC isoproteins (codon 259-Pro/Arg [259-P/R]), exhibiting unequal concentrations (TC 259-P > TC 259-R), and Caco-2 cells only secrete the phenotype 259-R. We investigated the relation between phenotypic and genetic TC polymorphism in HT-29 cells transfected with Caco-2 TC complementary DNA and in 159 healthy Caucasians. We found that codon 259-R is buried and, thus, the genetic polymorphism provides no explanation why the TCs from HT-29 and Caco-2 cells have different isoelectric points in nondenaturing isoelectric focusing (IEF). The newly translated TC in HT-29 cells from the Caco-2 complementary DNA recombinant plasmid had the same isoelectric point as the TC constitutively expressed in HT-29 cells, suggesting that TC phenotypic variability involves a specific cell folding of the protein. The codon 259 polymorphism was found to have a biallelic distribution: homozygotes P = 34.6%, heterozygotes R/P = 47.8%, and homozygotes R = 17.6%. In heterozygous samples, the IEF showed that the TC 259-P/TC 259-R ratio = 1.6. The blood apo-TC concentration of 259-P homozygous Caucasians was significantly higher than that of homozygous 259-R (P <.0001) and heterozygous (P <.0006) Caucasians. The heterozygotes 259-R/P had homocysteine concentration significantly higher than the homozygotes 259-R and 259-P (P =.02 and P =.01, respectively). In conclusion, TC codon-259 polymorphism affects TC plasma concentration and may interfere in vitamin B(12) cellular availability and homocysteine metabolism.     

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.     

Intracellular transport of high-density lipoprotein 3 in intestinal epithelial cells (Caco-2) is tubulin associated

BACKGROUND: A retroendocytotic pathway for high-density lipoprotein 3 (HDL(3)) in cultured intestinal epithelial cell lines has been described. In small intestinal crypt cells and Caco-2, HDL(3) is internalized, transported to lipid droplets and, after solubilization of these lipid droplets, resecreted. In the present study we examined the mechanisms of intracellular transport of HDL(3) in the Caco-2 cell line. METHODS: Apolipoprotein E free HDL(3 )was gold-labeled for transmission electron microscopy and 1, 1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine iodide [DiI(3)] labeled for fluorescence and confocal laser scanning microscopy. For tubulin desintegration Caco-2 cells were incubated with taxol, colchicine and beta- and gamma-lumicolchicine. Tubulin staining was performed using a FITC labeled antibody. Uptake of HDL(3) was quantified by FACS analysis. RESULTS: HDL(3) was rapidly internalized and found to be in contact with lipid droplets in the perinuclear region after 10 min. By transmission electron microscopy a frequent colocalization of HDL(3)-containing vesicles and tubular structures was demonstrated. The close association of HDL(3)-containing vesicles with fluorescence stained tubulin could be confirmed by confocal laser scanning microscopy. Preincubation of the cells with taxol and colchicine did not completely prevent internalization but reduced it during a 2-hour incubation period to less than 50% of the control cells. The transport of DiI(3)-labeled HDL(3) to the lipid droplets in the perinuclear region was almost completely blocked by taxol and colchicine. CONCLUSION: Internalization and intracellular transport of HDL(3) in intestinal epithelial cells (Caco-2) is dependent on a tubulin-mediated mechanism.     

Purified intestinal alkaline sphingomyelinase inhibits proliferation without inducing apoptosis in HT-29 colon carcinoma cells

Purpose Sphingomyelin (SM) hydrolysis by sphingomyelinase (SMase) has become an important signalling pathway, with the product ceramide implicated in regulation of cell growth, differentiation and apoptosis. Alkaline SMase is specifically located in the intestinal tract. Marked reductions of the enzyme activity have been found in sporadic colorectal carcinomas and in both adenomas and flat mucosa of patients with familial adenomatous polyposis, indicating an anti-proliferative role in colonic cell growth.Methods We examined the effects of a purified alkaline SMase from rat intestine and a bacterial neutral SMase on cell growth parameters in HT-29 colonic carcinoma cells.Results Alkaline SMase was found to inhibit proliferation of HT-29 cells in both dose-dependent and time-dependent manners. The threshold concentration of the enzyme was approximately 2.5 U/ml, and the maximum effect was obtained at approximately 20 U/ml, which inhibited the cell growth by 50%. The inhibition occurred rapidly, and maximum effect was reached after 12 h of incubation. Dose-dependent inhibition of DNA synthesis was also demonstrated. The effect of alkaline SMase was preceded and accompanied by increased hydrolysis of SM and production of ceramide. Neutral SMase with equivalent hydrolytic capacity did not inhibit cell growth. Alkaline SMase did not induce apoptosis in HT-29 cells. Alkaline SMase did not inhibit growth of IEC-6 cells.Conclusion Alkaline SMase, at doses that induce SM hydrolysis, inhibits growth of colon cancer cells. The inhibition is attributed to an anti-proliferative effect rather than an apoptotic effect.     

促肾上腺皮质释放因子对HT-29细胞中Toll样受体4/核因子-κB信号通路的影响

目的 观察促肾上腺皮质释放因子(corticotrophin-releasing factor CRF)对结肠上皮细胞系HT-29细胞中Toll样受体(TLR)4/核因子(NF)-κB的表达调控作用。方法 将HT-29细胞分为4组,正常对照组,脂多糖(LPS)组（IPS 20μg/ml刺激24 h）,CRF组(CRF 20 ng/ml刺激24h),CRF+LPS组（预先CRF孵育12h,更换细胞液后再与LPS孵育12h）。刺激结束后,RT-PCR法检测各组细胞中TLR4 mRNA的表达,提取细胞总蛋白,免疫印迹法检测各组细胞中TLR4和NF-κB p65蛋白表达水平。收集上清液,ELISA法检测各组细胞上清液中IL-8的表达。结果 LPS组TLR4 mRNA和蛋白表达水平为0.31±0.04和0.48±0.17,与正常对照组比较差异无统计学意义[0.28±0.02和0.45±0.12,t值分别＝0.216和0.712,P值均＞0.05],CRF组为1.05±0.06和1.08±0.21,与正常对照组相比明显增高（t值分别＝3.721和3.802,P值均＜0.05）,而CRF+ LPS组为1.68±0.05和1.81±0.18,更高于CRF组（t值分别＝4.816和3.918,P值均＜0.05）。各组HT-29细胞中NF-κB p65蛋白表达水平和细胞上清液中IL-8表达水平,与TLR4 mRNA和蛋白表达水平结果一致。结论 CRF不仅能直接刺激肠上皮细胞中TLR4/NF-κB通路活化,还可促进结肠上皮对LPS的反应增加,导致IL-8释放增多。     

丁酸盐与非甾体抗炎药对大肠腺癌细胞HT-29的作用

目的 观察丁酸盐和非甾体抗炎药（NSAIDs)对大肠腺癌细胞HT－29的作用,并探讨其可能的作用机制。方法 用酶联免疫法定量检测HT－29细胞所分泌的前列腺素（PG）E2;流式细胞仪检测细胞的凋亡率;电镜观察凋亡细胞的形态学。结果 丁酸盐可刺激细胞分泌大量的PGE2,阿司匹林和NS－398则抑制PGE2的分泌,3种药物均具有促进细胞凋亡的作用,且其作用呈浓度和时间依赖性（P＜0．05）;药物联用可使其作用不同程度地增强。结论 单用丁酸盐和2种NSAIDs制剂均有促凋亡作用,联用可通过下调环氧化酶－2的表达进一步增强疗效。     

Uptake of L-carnitine by a human intestinal epithelial cell line, Caco- 2

BACKGROUND & AIMS: The mechanism of intestinal uptake of L-carnitine is controversial. The aim of this study was to clarify the mechanism and regulation of L-carnitine uptake. METHODS: Uptake of [3H]-L-carnitine was measured across the apical membrane of confluent monolayers of Caco- 2 cells. RESULTS: [3H]-L-carnitine uptake was linear and appreciable for up to 7 minutes with minimal metabolic alteration, was temperature- and Na(+)-(but not pH-) dependent, and included a saturable component with an apparent Michaelis constant of 45.5 +/- 6.5 mumol/L and a maximum velocity of 83.5 +/- 5.6 nmol.mg protein-1.5 min-1. Unlabeled L- carnitine and its structurally related analogues significantly (P < 0.01) inhibited [3H]-L-carnitine uptake, whereas unrelated compounds were ineffective. L-Carnitine uptake was also energy-dependent, being significantly (P < 0.01) inhibited by metabolic inhibitors. Our results also suggested that a calmodulin- but not a protein kinase C- or protein kinase A-mediated pathway plays a role in regulating L- carnitine uptake by Caco-2 cells. CONCLUSIONS: L-carnitine uptake by intestinal epithelial cells (Caco-2) involves a carrier-mediated system that is temperature-, Na(+)-, and energy-dependent and seems to be under the regulation of a calmodulin-mediated pathway. (Gastroenterology 1996 Dec;111(6):1534-40)     

表皮生长因子对HT-29细胞内游离Ca~(2 )和C-AMP的影响

本文应用荧光比色法和放射免疫法动态检测了表皮生长因子对大肠癌HT-29细胞内Ca~(2 )和C-AMP水平的影响。结果发表EGF可呈剂量依赖性升高Ca~(2 )水平,而EGF-R抗体则可阻断此作用;EGF可短时降低C-AMP水平,提示Ca2 和C-AMP参于EGF作用的信息传递。     

Transcellular relocation of tetrahydrobiopterin across Caco-2 cells: A model study of tetrahydrobiopterin absorption through epithelial cells of intestinal mucosa

Summary  Oral administration of tetrahydrobiopterin (BH₄) has been known to be effective in treating BH₄-deficient patients. It has long been established that BH₄ is absorbed by the intestinal mucosa. However, the mechanism for translocation of BH₄ across epithelial cells has not been elucidated. In order to study BH₄ transport mechanisms, Caco-2 cells were employed in this study as an epithelial cell model. Caco-2 cells were cultured (2 × 10⁴ cells/0.3 cm² well) for 21 days in a 24-well format using Transwell, a porous membrane-based culture dish, at which point they had established themselves as a tight sheet with a definite polarity. When BH₄ (100 μmol/L) was given to cells from the apical side, a considerable translocation toward their basolateral side was noted. The rate of BH₄ movement was around 150 pmol/h per well. This was comparable to the highest rate of BH₄ uptake or its release so far obtained using a monolayer culture of Caco-2 cells on an ordinary plastic plate. The transcellular movement of BH₄ across the polar culture on the porous membrane was effectively prevented by benzbromarone (10 μmol/L), a well known inhibitor of a group of transporters including urate transporter (URAT1), organic anion transporters (OATs), and multidrug-resistance-associated proteins (MRPs). It was thus concluded that in Caco-2 cells, BH₄ moved across the cell interior in a rapid ligand-specific manner that was driven by a transporter. Competing interests: None declared References to electronic databases: Dihydrofolate reductase: EC 1.5.1.3. Presented at the International Conference on Tetrahydrobiopterin, PKU, and NOS, 23–28 March 2008, St Moritz, Champfér, Switzerland     

神经酰胺对结肠癌HT-29细胞凋亡和增殖细胞核抗原表达的影响

目的 探索神经酰胺(C_2-cer)影响人结肠癌HT-29细胞增殖、凋亡和增殖细胞核抗原(PCNA)表达.方法 12.5、25 μmol/L的C_2-cer处理HT-29细胞,用MTT法、流式细胞仪、激光共聚焦显微镜、Western印迹等方法检测HT-29细胞增殖、凋亡和PCNA表达.结果 以12.5、25 μmol/L的C_2-cer处理HT-29细胞,细胞增殖受到抑制,细胞凋亡明显增加,PCNA表达明显降低,并呈剂量-效应关系.结论 C_2-cer可诱导细胞凋亡,该效应可能与下调PCNA表达有关.     

舒林酸对结肠腺癌HT-29细胞增殖调控的实验研究

目的 观察舒林酸对结肠腺癌ＨＴ－２９细胞增殖的影响,探讨其作用机制。方法 采用ＭＴＴ比色法观察舒林酸对ＨＴ－２９细胞增殖的影响;采用流式细胞仪检测舒林酸对ＨＴ－２９细胞周期的影响,同时结合ＤＮＡ电泳和透射电镜观察舒林酸对ＨＴ－２９细胞有无促凋亡作用。结果 舒林酸可抑制ＨＴ－２９细胞增殖,使Ｇ０／Ｇ１期细胞比例增高,Ｓ期比例降低,７２ｈ后,ＨＴ－２９细胞凋亡分别上升至１２．５＾、１５．４＾和２４．２     

Hydrophilic and hydrophobic bile acids exhibit different cytotoxicities through cytolysis, interleukin-8 synthesis and apoptosis in the intestinal epithelial cell lines. IEC-6 and Caco-2 cells

BACKGROUND: Bile acids have been shown to exhibit varying degrees of cytotoxicity, depending on their hydrophobic-hydrophilic balance. We have recently reported the strong cytotoxicity of hyodeoxycholic acid (HDCA), and the aim of the present study is to investigate the mechanisms underlying the cytotoxicity of HDCA. METHODS: The intestinal cell lines IEC-6 and Caco-2 cells were used. The cytotoxicities of various bile acids were evaluated using the MTS assay; their cytolytic effects were measured using the LDH release assay. The induction of apoptosis was determined by the specific figure changes in the cellular cytoplasm and nucleus, including DNA ladder formations. IL-8 synthesis induced by the bile acids was measured using an ELISA assay. RESULTS: The bile acids induced cytotoxic effects, LDH release, IL-8 synthesis and apoptosis, depending on their hydrophobic properties. On the other hand, HDCA induced strong cytotoxicity, apoptosis and IL-8 synthesis but not cytolysis, although HDCA has a hydrophilic nature. In addition, HDCA exerted the strongest effects on dispersing monolayer cells. CONCLUSIONS: These results strongly suggest that HDCA induces cytotoxicity through its ability to induce apoptosis rather than its detergent effect.