Regulation of human colonic cell line proliferation and phenotype by sodium butyrate

Gut homeostasis, injury, and healing: New therapeutic targets

The integrity of the gastrointestinal mucosa plays a crucial role in gut homeostasis, which depends upon the balance between mucosal injury by destructive factors and healing via protective factors. The persistence of noxious agents such as acid, pepsin, nonsteroidal anti-inflammatory drugs, or Helicobacter pylori breaks down the mucosal barrier and injury occurs. Depending upon the size and site of the wound, it is healed by complex and overlapping processes involving membrane resealing, cell spreading, purse-string contraction, restitution, differentiation, angiogenesis, and vasculogenesis, each modulated by extracellular regulators. Unfortunately, the gut does not always heal, leading to such pathology as peptic ulcers or inflammatory bowel disease. Currently available therapeutics such as proton pump inhibitors, histamine-2 receptor antagonists, sucralfate, 5-aminosalicylate, antibiotics, corticosteroids, and immunosuppressants all attempt to minimize or reduce injury to the gastrointestinal tract. More recent studies have focused on improving mucosal defense or directly promoting mucosal repair. Many investigations have sought to enhance mucosal defense by stimulating mucus secretion, mucosal blood flow, or tight junction function. Conversely, new attempts to directly promote mucosal repair target proteins that modulate cytoskeleton dynamics such as tubulin, talin, Ehm², filamin-a, gelsolin, and flightless I or that proteins regulate focal adhesions dynamics such as focal adhesion kinase. This article summarizes the pathobiology of gastrointestinal mucosal healing and reviews potential new therapeutic targets.

Butyrate and the Intestinal Epithelium: Modulation of Proliferation and Inflammation in Homeostasis and Disease

The microbial metabolite butyrate serves as a link between the intestinal microbiome and epithelium. The monocarboxylate transporters MCT1 and SMCT1 are the predominant means of butyrate transport from the intestinal lumen to epithelial cytoplasm, where the molecule undergoes rapid β-oxidation to generate cellular fuel. However, not all epithelial cells metabolize butyrate equally. Undifferentiated colonocytes, including neoplastic cells and intestinal stem cells at the epithelial crypt base preferentially utilize glucose over butyrate for cellular fuel. This divergent metabolic conditioning is central to the phenomenon known as “butyrate paradox”, in which butyrate induces contradictory effects on epithelial proliferation in undifferentiated and differentiated colonocytes. There is evidence that accumulation of butyrate in epithelial cells results in histone modification and altered transcriptional activation that halts cell cycle progression. This manifests in the apparent protective effect of butyrate against colonic neoplasia. A corollary to this process is butyrate-induced inhibition of intestinal stem cells. Yet, emerging research has illustrated that the evolution of the crypt, along with butyrate-producing bacteria in the intestine, serve to protect crypt base stem cells from butyrate’s anti-proliferative effects. Butyrate also regulates epithelial inflammation and tolerance to antigens, through production of anti-inflammatory cytokines and induction of tolerogenic dendritic cells. The role of butyrate in the pathogenesis and treatment of intestinal neoplasia, inflammatory bowel disease and malabsorptive states is evolving, and holds promise for the potential translation of butyrate’s cellular function into clinical therapies.

Lactobacillus rhamnosus GG and Saccharomyces cerevisiae boulardii exert synergistic antipathogenic activity in vitro against enterotoxigenic Escherichia coli

Short-term colonic in vitro batch incubations were performed to elucidate the possible synergistic effects of Lactobacillus rhamnosus GG (CNCM-I-4798) and Saccharomyces cerevisiae boulardii (CNCM-I-1079) (associated in Smebiocta/Smectaflora Protect®) on the colonic microbial fermentation process, as well as their antipathogenic activity against enterotoxigenic Escherichia coli (LMG2092) (ETEC). These incubations adequately simulate the native microbiota and environmental conditions of the proximal colon of both adult and toddler donors, including the colonic mucosal layer. Results indicated that both strains were capable of growing together without showing antagonistic effects. Co-cultivation of both strains resulted in increased butyrate (stimulated by L. rhamnosus GG), propionate (stimulated by S. boulardii), and ethanol (produced by S. boulardii) production compared to the control incubations, revealing the additive effect of both strains. After inoculation of ETEC under simulated dysbiotic conditions, a 40 and 46% reduction in the concentration of ETEC was observed upon addition of both strains during the experiments with the adult and toddler donor, respectively. Furthermore, ETEC toxin levels decreased upon S. boulardii inoculation, probably due to proteolytic activity of this strain, with a synergistic effect being observed upon co-cultivation of L. rhamnosus GG and S. boulardii resulting in a reduction of 57 and 46% for the adult and toddler donor, respectively. Altogether, the results suggest that both probiotics together may help microbiota functionality, in both adults and toddlers and under healthy or impaired conditions, which could be of great interest when the colonic microbiota is dysbiotic and therefore sensitive to pathogenic invasion such as during antibiotic treatment.

Arabinoxylo-Oligosaccharides and Inulin Impact Inter-Individual Variation on Microbial Metabolism and Composition, Which Immunomodulates Human Cells

Fecal batch fermentations coupled to cocultures of epithelial cells and macrophages were used to compare how arabinoxylo-oligosaccharides (AXOS) and inulin modulate gut microbial activity and composition of three different human donors and subsequently the epithelial permeability and immune response. Both inulin and AXOS decreased the pH during incubation (-1.5 pH units), leading to increased productions of acetate, propionate, and butyrate. Differences in terms of metabolites production could be linked to specific microbial alterations at genus level upon inulin/AXOS supplementation (i.e., Bifidobacterium, Bacteroides, Prevotella and unclassified Erysipelotrichaceae), as shown by 16S-targeted Illumina sequencing. Both products stimulated gut barrier and immune function with increases in TEER, NF-KB, IL-10, and IL-6. Ingredients with different structures selectively modulate the microbiota of a specific donor leading to differential changes at metabolic level. The extent of this effect is donor specific and is linked to a final specific modulation of the host's immune system.

The Gut Microbiota from Lean and Obese Subjects Contribute Differently to the Fermentation of Arabinogalactan and Inulin

Background

An aberrant metabolic activity or a compositional alteration of the gut microbiota has been proposed as a factor that makes us more prone to disease. Therefore, we explored the effect of two dietary fibers (arabinogalactan and inulin) on the microbiota from lean and obese subjects during 72 h in vitro fermentation experiments using the validated TNO dynamic in vitro model of the proximal colon: TIM-2. Metabolically, arabinogalactan fermentation showed a higher production of propionate when compared to n-butyrate in the obese microbiota fermentations. In general, lean microbiota produced more n-butyrate from the fermentation of both substrates when compared to the obese microbiota. Furthermore, the obese microbiota extracted more energy from the fermentation of both fibers.

Results

Compositionally, bacteria belonging to Gemmiger, Dorea, Roseburia, Alistipes, Lactobacillus and Bifidobacterium genera were found to be highly abundant or stimulated by the prebiotics in the lean microbiota suggesting a potential role in leanness. Furthermore, a significant correlation between known butyrogenic strains including B. adolescentis, an unclassified Bifidobacterium and F. prausnitzii with this metabolite in the fermentation of inulin in both microbiotas was found.

Conclusions

Although supplementary in vivo studies are needed, the current study provides more evidence for the consumption of specific ingredients with the aim of modulating the gut microbiota in the context of obesity.

The correlation between the expression of differentiation markers in rat small intestinal mucosa and the transcript levels of schlafen 3

IMPORTANCE

The normal absorptive function and structural maintenance of the intestinal mucosa depend on a constant process of proliferation of enterocytic stem cells followed by progressive differentiation toward a mature phenotype. The mechanisms that govern enterocytic differentiation in the mucosa of the small intestine are poorly understood.

OBJECTIVE

To determine whether schlafen 3 (but not other schlafen proteins) act in vivo and whether its effects are limited to the small intestine. We have previously demonstrated in nonmalignant rat intestinal IEC-6 cells that schlafen 3 levels correlate with the expression of various differentiation markers in vitro in response to differentiation stimuli.

DESIGN

Randomized controlled experiment.

SETTING

Animal science laboratory.

PARTICIPANTS

Male Sprague-Dawley rats 8 to 13 weeks old.

MAIN OUTCOMES AND MEASURES

Messenger RNA (mRNA) from jejunal and colonic mucosa was isolated, and transcript levels of schlafen proteins 1, 2, 3, 4, 5, 13, and 14; sucrase isomaltase (SI); dipeptidyl peptidase 4 (Dpp4); glucose transporter type 2 (Glut2); and villin were measured by quantitative reverse transcriptase-polymerase chain reaction. We tested parallel variations in protein levels by Western blotting and Dpp4 enzyme activity.

RESULTS

The transcript level of schlafen 3 (Slfn3) correlated with the levels of the differentiation markers SI, Dpp4, Glut2, and villin. However, the expression of schlafen proteins 1, 2, 4, 5, 13, and 14 did not correlate with the expression of the differentiation markers. The mucosal mRNA levels of Slfn3, SI, Glut2, and Dpp4 were all substantially higher in the rat jejunum than in colonic mucosa by a mean (SE) factor of 51.0 (13.2) for 6 rats (P < .05), 599 (99) for 8 rats (P < .01), 12.5 (5.5) for 8 rats (P < .01), and 14.0 (3.9) for 8 rats (P < .01), respectively. In IEC-6 cells, infection with adenovirus-expressing GFP-tagged Slfn3 significantly increased Slfn3 expression and Dpp4-specific activity compared with GFP-expressing virus (in 6 rats; P < .05).

CONCLUSIONS AND RELEVANCE

Taken together with our previous in vitro observations, the results suggest that small intestinal enterocytic epithelial differentiation in rats may be regulated by Slfn3 in vivo, as in vitro, and that these effects may be specific to the small intestinal enterocytic phenotype as opposed to that of the mature colonocyte. Slfn3 human orthologs may be targeted to stimulate intestinal differentiation in patients with short bowel syndrome.

Different human gut models reveal the distinct fermentation patterns of Arabinoxylan versus inulin

Different in vitro models have been developed to assess how food compounds affect the human gut microbiota. Using two such models (SHIME(R) and TIM-2), we compared how long-chain arabinoxylan (LC-AX), a wheat-derived potentially prebiotic fiber, and inulin (IN), a well-established prebiotic compound, modulate SCFA production and bifidobacteria composition. While both the SHIME and TIM-2 differ in experimental design, they both demonstrated that LC-AX and IN specifically increased the health-promoting metabolites propionate and butyrate, respectively. Furthermore, LC-AX stimulated Bifidobacterium longum, while IN stimulated other bifidobacteria including Bifidobacterium adolescentis. The SHIME experiment also revealed that effects of LC-AX were more persistent during the 2-week wash-out period. These results confirm a recent in vivo study, during which humanized rats were treated with the same LC-AX/IN. In conclusion, results from different human gut models suggest that, besides IN, LC-AX are promising prebiotic candidates with high specificity toward Bifidobacterium longum and a selective propionate increase.

Arabinoxylans and inulin differentially modulate the mucosal and luminal gut microbiota and mucin-degradation in humanized rats

The endogenous gut microbiota affects the host in many ways. Prebiotics should favour beneficial intestinal microbes and thus improve host health. In this study, we investigated how a novel class of potential prebiotic long-chain arabinoxylans (LC-AX) and the well-established prebiotic inulin (IN) modulate the gut microbiota of humanized rats. Six weeks after axenic rats were inoculated with a human faecal microbiota, their colonic microbiota was similar to this inoculum (∼ 70%), whereas their caecal microbiota was enriched with Verrucomicrobia and Firmicutes concomitant with lower abundance of Bacteroidetes. Moreover, different Bifidobacterium species colonized the lumen (B. adolescentis) and mucus (B. longum and B. bifidum). Both LC-AX and IN increased SCFA levels and induced a shift from acetate towards health-promoting propionate and butyrate respectively. By applying a high-resolution phylogenetic micro-array (HITChip) at the site of fermentation (caecum), IN and LC-AX were shown to stimulate bacterial groups with known butyrate-producers (Roseburia intestinalis, Eubacterium rectale, Anaerostipes caccae) and bifidobacteria (B. longum) respectively. Prebiotic administration also resulted in lower caecal abundances of the mucin-degrading Akkermansia muciniphila and potentially more mucin production by the host. Both factors might explain the increased caecal mucin levels for LC-AX (threefold) and IN (sixfold). These mucins were degraded along the colon, resulting in high faecal abundances of Akkermansia muciniphila for LC-AX and especially IN-treated rats. Finally, the microbial changes caused an adaptation period for the host with less weight gain, after which the host fine-tuned the interaction with this altered microbiota. Our results demonstrate that next to IN, LC-AX are promising prebiotic compounds by stimulating production of health-promoting metabolites by specific microbes in the proximal regions. Further, prebiotic supplementation shifted mucin degradation to distal regions, where mucin-degraders may produce beneficial metabolites (e.g. propionate by Akkermansia muciniphila), so that prebiotics may potentially improve gut health along the entire length of the intestine.

Comparative analysis of Korean human gut microbiota by barcoded pyrosequencing

Human gut microbiota plays important roles in harvesting energy from the diet, stimulating the proliferation of the intestinal epithelium, developing the immune system, and regulating fat storage in the host. Characterization of gut microbiota, however, has been limited to western people and is not sufficiently extensive to fully describe microbial communities. In this study, we investigated the overall composition of the gut microbiota and its host specificity and temporal stability in 20 Koreans using 454-pyrosequencing with barcoded primers targeting the V1 to V3 region of the bacterial 16S rRNA gene. A total of 303,402 high quality reads covered each sample and 8,427 reads were analyzed on average. The results were compared with those of individuals from the USA, China and Japan. In general, microbial communities were dominated by five previously identified phyla: Actinobacteria, Firmicutes, Bacteroidetes, Fusobacteria, and Proteobacteria. UPGMA cluster analysis showed that the species composition of gut microbiota was host-specific and stable over the duration of the test period, but the relative abundance of each member fluctuated. 43 core Korean gut microbiota were identified by comparison of sequences from each individual, of which 15 species level phylotypes were related to previously-reported butyrate-producing bacteria. UniFrac analysis revealed that human gut microbiota differed between countries: Korea, USA, Japan and China, but tended to vary less between individual Koreans, suggesting that gut microbial composition is related to internal and external characteristics of each country member such as host genetics and diet styles.

Butyrate induces expression of 17β-hydroxysteroid dehydrogenase type 1 in HT29 and SW707 colorectal cancer cells

Epidemiological studies have revealed that butyrate and 17β-estradiol (E2) may decrease the incidence of colorectal cancer (CRC). In peripheral tissue, E2 can be produced locally by 17β-hydroxysteroid dehydrogenase 1 (HSD17B1) estrone (E1) reduction. Using quantitative real-time polymerase chain reaction and western blotting analysis, we found that sodium butyrate significantly upregulates HSD17B1 long and short transcripts and protein levels in HT29 and SW707 CRC cells. Chromatin immunoprecipitation analysis showed that upregulation of these transcript levels correlated with an increase in binding of Polymerase II to proximal and distal promoters of HSD17B1. Moreover, we observed that upregulation of HSD17B1 protein levels was associated with increased conversion of E1 to E2 in HT29 and SW707 CRC cells. Since sodium butyrate increases the conversion of E1 to E2, our findings may support the validity of butyrate in the prophylaxis of CRC incidence.

Post-translational modulation of CD133 expression during sodium butyrate-induced differentiation of HT29 human colon cancer cells: implications for its detection

The CD133 molecule has been proposed as a surface marker of cancer stem cells in several human malignancies, including colon cancers. The function and the mechanisms regulating CD133 expression remain unknown. The HT29 human colon cancer cells undergo differentiation following treatment with various agents and represent a useful in vitro model of colon differentiation. This study evaluated the behavior of CD133 during sodium butyrate-induced differentiation of HT29 cells. Treatment with sodium butyrate induced a progressive decrease of CD133 expression, as assessed by flow cytometry using the AC133 monoclonal antibody. Indeed, expression of CD133, which was about 47% in untreated control cells, gradually decreased down to about 3% after 72 h in a time- and dose-dependent manner. No relationship was observed between CD133 protein evaluated by flow cytometry and mRNA expression level, and no changes were detected in the methylation status of the CD133 gene promoter during HT29 differentiation. Moreover, the expression of the CD133 protein, evaluated by Western blot analysis using a specific anti-CD133 antibody directed against the C-terminal intracytoplasmic region of human CD133 protein, did not correlate with flow cytometry results. Different results were also obtained using the two antibodies to analyze the expression of the CD133 molecule in human colon cancers. These findings demonstrate that membrane expression of the CD133 stem cell marker might undergo a complex regulation during differentiation of colon cells and suggest that HT29 cells are a useful in vitro model to study the mechanisms involved in this regulation which likely occurs at a post-transcriptional level.

Differential antineoplastic effects of butyrate in cells with and without a functioning DNA mismatch repair

The aim of this study was to investigate the differential antineoplastic effects of butyrate in cells with and without a functional mismatch repair and to determine the molecular mechanisms underlying these effects. SW48 colon cancer cells in which the MLH1 gene is silenced by promoter hypermethylation and demethylated SW48 cells in which the MLH1 gene is reexpressed were treated with butyrate (0-5mM) for 8 days and the effects on cell number, MLH1 gene promoter methylation, and expression of two cell cycle regulatory genes, CDK4 and GADD45A, were assessed. Butyrate suppressed viable cell number (P < 0.001) and reduced MLH1 promoter methylation (P < 0.05) in SW48 cells. However, in demethylated SW48 cells, butyrate caused an increase in viable cells (P < 0.05) and promoter methylation (P < 0.05). CDK4 expression was downregulated by butyrate exposure, but the effect was significantly greater for demethylated SW48 cells (P = 0.025). Butyrate treatment caused upregulation of GADD45A expression in SW48 cells but downregulation of GADD45A expression in demethylated SW48 cells (P = 0.045). This study supports the hypothesis that butyrate has more potent antineoplastic effects on colon cancer cells with MLH1 dysfunction. Differential expression of key cell cycle regulatory genes may explain some of the molecular mechanisms underlying these effects.

Short-chain fatty acid-mediated effects on erythropoiesis in primary definitive erythroid cells

Short-chain fatty acids (SCFAs; butyrate and propionate) up-regulate embryonic/fetal globin gene expression through unclear mechanisms. In a murine model of definitive erythropoiesis, SCFAs increased embryonic beta-type globin gene expression in primary erythroid fetal liver cells (eFLCs) after 72 hours in culture, from 1.7% (+/- 1.2%) of total beta-globin gene expression at day 0 to 4.9% (+/- 2.2%) in propionate and 5.4% (+/- 3.4%) in butyrate; this effect was greater in butyrate plus insulin/erythropoietin (BIE), at 19.5% (+/- 8.3%) compared with 0.1% (+/- 0.1%) in ins/EPO alone (P < .05). Fetal gamma-globin gene expression was increased in human transgene-containing eFLCs, to 35.9% (+/- 7.0%) in BIE compared with 4.4% (+/- 4.2%) in ins/EPO only (P < .05). Embryonic globin gene expression was detectable in 11 of 15 single eFLCs treated with BIE, but in0 of 15 ins/EPO-only treated cells. Butyrate-treated [65.5% (+/- 9.9%)] and 77.5% (+/- 4.0%) propionate-treated eFLCs were highly differentiated in culture, compared with 21.5% (+/- 3.5%) in ins/EPO (P < .005). Importantly, signaling intermediaries, previously implicated in induced embryonic/fetal globin gene expression (STAT5, p42/44, and p38), were not differentially activated by SCFAs in eFLCs; but increased bulk histone (H3) acetylation was seen in SCFA-treated eFLCs. SCFAs induce embryonic globin gene expression in eFLCS, which are a useful short-term and physiologic primary cell model of embryonic/fetal globin gene induction during definitive erythropoiesis.

Fermentation of Resistant Starches: Influence of In Vitro Models on Colon Carcinogenesis

Resistant starch type 2 (RS2) and type 3 (RS3) containing preparations were digested using a batch (a) and a dynamic in vitro model (b). Furthermore, in vivo obtained indigestible fractions from ileostomy patients were used (c). Subsequently these samples were fermented with human feces with a batch and a dynamic in vitro method. The fermentation supernatants were used to treat CACO2 cells. Cytotoxicity, anti-genotoxicity against hydrogen peroxide (comet assay) and the effect on barrier function measured by trans-epithelial electrical resistance were determined. Dynamically fermented samples led to high cytotoxic activity, probably due to additional compounds added during in vitro fermentation. As a consequence only batch fermented samples were investigated further. Batch fermentation of RS resulted in an anti-genotoxic activity ranging from 9-30% decrease in DNA damage for all the samples, except for RS2-b. It is assumed that the changes in RS2 structures due to dynamic digestion resulted in a different fermentation profile not leading to any anti-genotoxic effect. Additionally, in vitro batch fermentation of RS caused an improvement in integrity across the intestinal barrier by approximately 22% for all the samples. We have demonstrated that batch in vitro fermentation of RS2 and RS3 preparations differently pre-digested are capable of inhibiting the initiation and promotion stage in colon carcinogenesis in vitro.

Activated protein C promotes breast cancer cell migration through interactions with EPCR and PAR-1

Activated protein C (APC) is a serine protease that regulates thrombin (IIa) production through inactivation of blood coagulation factors Va and VIIIa. APC also has non-hemostatic functions related to inflammation, proliferation, and apoptosis through various mechanisms. Using two breast cancer cell lines, MDA-MB-231 and MDA-MB-435, we investigated the role of APC in cell chemotaxis and invasion. Treatment of cells with increasing APC concentrations (1-50 microg/ml) increased invasion and chemotaxis in a concentration-dependent manner. Only the active form of APC increased invasion and chemotaxis of the MDA-MB-231 cells when compared to 3 inactive APC derivatives. Using a modified "checkerboard" analysis, APC was shown to only affect migration when plated with the cells; therefore, APC is not a chemoattractant. Blocking antibodies to endothelial protein C receptor (EPCR) and protease-activated receptor-1 (PAR-1) attenuated the effects of APC on chemotaxis in the MDA-MB-231 cells. Finally, treatment of the MDA-MB-231 cells with the proliferation inhibitor, Na butyrate, showed that APC did not increase migration by increasing cell number. Therefore, APC increases invasion and chemotaxis of cells by binding to the cell surface and activating specific signaling pathways through EPCR and PAR-1.

Differential expression proteomics of human colon cancer

The focus of this study was to use differential protein expression to investigate operative pathways in early stages of human colon cancer. Colorectal cancer represents an ideal model system to study the development and progression of human tumors, and the proteomic approach avoids overlooking posttranslational modifications not detected by microarray analyses and the limited correlation between transcript and protein levels. Colon cancer samples, confined to the intestinal wall, were analyzed by expression proteomics and compared with matched samples from normal colon tissue. Samples were processed by two-dimensional gel electrophoresis, and spots differentially expressed and consistent across all patients were identified by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry analyses and by Western blot analyses. After differentially expressed proteins and their metabolic pathways were analyzed, the following main conclusions were achieved for tumor tissue: 1) a shift from beta-oxidation, as the main source of energy, to anaerobic glycolysis was observed owed to the alteration of nuclear- versus mitochondrial-encoded proteins and other proteins related to fatty acid and carbohydrate metabolism; 2) lower capacity for Na(+) and K(+) cycling; and 3) operativity of the apoptosis pathway, especially the mitochondrial one. This study of the human colon cancer proteome represents a step toward a better understanding of the metabolomics of colon cancer at early stages confined to the intestinal wall.

Induction of Human P-Glycoprotein in Caco-2 cells: Development of a Highly Sensitive Assay System for P-Glycoprotein-Mediated Drug Transport

The aim of this work is to develop a highly sensitive assay system for P-gp-mediated transport by using two methods, induction of P-gp and short-term culture of Caco-2 cells. To induce P-gp in Caco-2 cells, cells were cultured in vinblastine-containing medium. The mRNA level of P-gp was approximately 7-fold higher in Caco-2 cells cultured with vinblastine (P-gp-induced Caco-2 cells) than in control cells. Western blot analysis showed a significant increase in P-gp expression. After cell differentiation, the mRNA level of P-gp was downregulated, however, P-gp-induced Caco-2 cells still possessed a 5.6-fold higher mRNA level of P-gp compared to control cells. Polarized transport of substrate drugs was greater in the monolayer of P-gp-induced cells than in that of control cells. Moreover, we found that P-gp expression in Caco-2 cells could be further enhanced by applying the higher concentration of vinblastine. Transport activity of P-gp in Caco-2 cells cultured with higher concentration of vinblastine was markedly higher than that in P-gp-induced Caco-2 cells and was comparable with that in MDR1-MDCKII cells. In conclusion, this study provided a stable and highly sensitive in vitro assay system that can identify compounds that are subject to P-gp-mediated efflux.

Butyrate-induced differentiation of colon cancer cells is PKC and JNK dependent

Butyric acid, a short-chain fatty acid physiologically present in human large gut, is derived from bacterial fermentation of complex carbohydrates. It has been shown to reduce the growth and motility of colon cancer cell lines and to induce cell differentiation and apoptosis. Apoptosis is considered a result of normal colonocyte terminal differentiation in vivo. The aim of this study was to characterize the cellular mechanisms regulating differentiation of colon cancer cells stimulated with sodium butyrate (NaB). The two human colon cancer cell lines Caco-2 and HT-29 were treated with NaB at physiologically relevant concentrations. Alkaline phosphatase (ALP) activity, a marker of colonocyte differentiation, was increased 48 hr after treatment with 1 mM NaB. Higher doses of NaB (5 and 10 mM) induced apoptosis of the cells and failed to stimulate the colonocyte differentiation. Therefore, we assumed that butyrate augments cell differentiation and induces apoptosis, acting via various intracellular mechanisms, and butyrate-mediated programmed cell death cannot be considered a consequence of colonocyte terminal differentiation. The effect of NaB on ALP activity was significantly attenuated in the presence of inhibitors of protein kinase C and JNK. Inhibition of MEK-ERK signal transduction pathways augmented the impact of butyrate on colonocyte differentiation. These results suggest that butyrate could influence the colonocyte differentiation via modulation of the activity of cellular protein kinases and signal transduction.

Colon cancer: genomics and apoptotic events

Colon cancer is the third most common cancer globally. The risk of developing colon cancer is influenced by a number of factors that include age and diet, but is primarily a genetic disease, resulting from oncogene over-expression and tumour suppressor gene inactivation. The induction and progression of the disease is briefly outlined, as are the cellular changes that occur in its progression. While colon cancer is uniformly amenable to surgery if detected at the early stages, advanced carcinomas are usually lethal, with metastases to the liver being the most common cause of death. Oncogenes and genetic mutations that occur in colon cancer are featured. The molecules and signals that act to eradicate or initiate the apoptosis cascade in cancer cells, are elucidated, and these include caspases, Fas, Bax, Bid, APC, antisense hTERT, PUMA, 15-LOX-1, ceramide, butyrate, tributyrin and PPARgamma, whereas the molecules which promote colon cancer cell survival are p53 mutants, Bcl-2, Neu3 and COX-2. Cancer therapies aimed at controlling colon cancer are reviewed briefly.

Laboratory efforts to cultivate noroviruses

Noroviruses (NoVs) are a leading cause of gastroenteritis worldwide and are recognized as the foremost cause of foodborne illness. Despite numerous efforts, routine cell cultures have failed to yield replicating NoV. This paper describes methods used to try to grow NoV in vitro in two laboratories. Cells (A549, AGS, Caco-2, CCD-18, CRFK, CR-PEC, Detroit 551, Detroit 562, FRhK-4, HCT-8, HeLa, HEC, HEp-2, Ht-29, HuTu-80, I-407, IEC-6, IEC-18, Kato-3, L20B, MA104, MDBK, MDCK, RD, TMK, Vero and 293) were cultured on solid or permeable surfaces. Differentiation was induced using cell culture supplements such as insulin, DMSO and butyric acid. In some cases, the cells and the NoV-containing stool samples were treated with bioactive digestive additives. Variables evaluated in cultivation experiments included the method of preparation of the virus inoculum, the genotype of the virus, conditions for maintenance of cell monolayers, additives in the maintenance medium and the method of inoculation of the cells. Serial blind passage studies were performed routinely. In addition to evaluation for CPE, evidence of virus replication was sought using immunofluorescent assays to detect newly produced viral capsid antigen and RT-PCR assays to detect the viral genome. Although some infected cultures remained NoV positive by RT-PCR for up to five passages and an occasional cell in a monolayer showed evidence of specific immunofluorescence, no reproducible NoV-induced CPE was observed and all RT-PCR results that were positive initially were negative following continued passaging. Thus, attempts to develop a method for the cultivation of NoV were unsuccessful.

Butyrate-treated colonic Caco-2 cells exhibit defective integrin-mediated signaling together with increased apoptosis and differentiation

We previously reported that the enterocytic differentiation of human colonic Caco-2 cells correlated with alterations in integrin signaling. We now investigated whether differentiation and apoptosis of Caco-2 cells induced by the short-chain fatty acid butyrate (NaBT) was associated with alterations in the integrin-mediated signaling pathway with special interest in the expression and activity of focal adhesion kinase (FAK), of the downstream phosphatidylinositol 3'-kinase (PI 3-kinase)-Akt pathway and in the role of the nuclear factor kappaB (NF-kappaB). NaBT increased the level of sucrase. It induced apoptosis as shown by: (1) decreased Bcl-2 and Bcl-X(L) proteins and increased Bax protein; (2) activation of caspase-3; and (3) increased shedding of apoptotic cells in the medium. This effect was associated with defective integrin-mediated signaling as shown by: (1) down-regulation of beta1 integrin expression; 2) decreased FAK expression and tyrosine phosphorylation; (3) concerted alterations in cytoskeletal and structural focal adhesions proteins (talin, ezrin); and (4) decreased FAK ability to associate with PI 3-kinase. However, in Caco-2 cells, beta1-mediated signaling failed to be activated downstream of FAK and PI 3-kinase at the level of Akt. Transfection studies show that NaBT treatment of Caco-2 cells promoted a significant activation of the NF-kappaB which was probably involved in the NaBT-induced apoptosis. Our results indicate that the prodifferentiating agent NaBT induced apoptosis of Caco-2 cells probably through NF-kappaB activation together with a defective beta1 integrin-FAK-PI 3-kinase pathways signaling.

Oncogenic ras alters sensitivity of mouse colonocytes to butyrate and fatty acid mediated growth arrest and apoptosis

Docosahexaenoic acid (DHA) and butyrate favorably modulate colonocyte proliferation and apoptosis. In order to elucidate how oncogenic Ras modulates responses to these chemopreventive nutrients, we incubated isogenic non-transformed and Ras malignant transformed mouse colon cells with butyrate and DHA or linoleic acid (LA). Combining DHA with 1mM butyrate decreased proliferation relative to LA or no PUFA treatment in both cell lines. At a higher butyrate dose (5mM), caspase 3 activity was elevated to a greater extent in Ras transformed cells. Only non-transformed cells were sensitive to the apoptogenic effects of DHA, indicating that Ras transformation alters sensitivity to dietary chemopreventive agents.

Expression and regulation of CD97 in colorectal carcinoma cell lines and tumor tissues

The expression of CD97, a member of the EGF-TM7 family with adhesive properties, is proportional to the aggressiveness and lymph node involvement in thyroid tumors. CD97 has never been systematically investigated in other tumors. First, we examined colorectal carcinoma cell lines (n = 18) for CD97 expression and regulation. All cell lines were CD97-positive. The level of CD97 in each line correlated with migration and invasion in vitro. This result was confirmed in CD97-inducible Tet-off HT1080 cells. Transforming growth factor-beta, which inhibits proliferation in transforming growth factor-beta-sensitive LS513 and LS1034 cells, down-regulated CD97 in these cell lines. Examining CD97 during sodium butyrate-induced cell differentiation of Caco-2 cells, we could demonstrate a CD97-decreasing effect. Second, we screened 81 colorectal adenocarcinomas by immunohistology for expression of CD97. Normal colorectal epithelium is CD97-negative. Seventy-five of 81 of the carcinomas expressed CD97. The strongest staining for CD97 occurred in scattered tumor cells at the invasion front compared to cells located within solid tumor formations of the same tumor. Carcinomas with more strongly CD97-stained scattered tumor cells showed a poorer clinical stage as well as increased lymph vessel invasion compared to cases with uniform CD97 staining. In summary, CD97 expression correlates with dedifferentiation, migration, and invasion in colorectal tumor cell lines. Moreover, more strongly CD97-stained tumor cells at the invasion front of colorectal carcinomas indicate the involvement of the molecule in tumor migration and invasion.

Resveratrol enhances the differentiation induced by butyrate in caco-2 colon cancer cells

Butyrate, a short-chain fatty acid produced in the colon by microbial fermentation of fiber, inhibits growth of colonic carcinoma cells while inducing differentiation. Resveratrol, a plant polyphenol found in red wine and peanuts, has been shown to exert chemopreventive properties on colon cancer cells. The aim of this study was to determine whether resveratrol modulates the effects of butyrate on Caco-2, a colonic adenocarcinoma cell line. The growth inhibitory effect of resveratrol (50 micromol/L) was more powerful than that of butyrate (2 mmol/L). Butyrate did not intensify the inhibition of proliferation exerted by resveratrol. Although the polyphenol enhanced the differentiation-inducing effect of butyrate, it did not elevate alkaline phosphatase activity or E-cadherin protein expression, markers of epithelial differentiation, when applied alone. Butyrate-induced transforming growth factor-beta1 secretion was inhibited by resveratrol. Treatment with the combination of resveratrol and butyrate attenuated levels of p27(Kip1), whereas resveratrol enhanced butyrate's effect on the induction of p21(Waf1/Cip1) expression. These data demonstrate a possible combined chemopreventive effect of two substances naturally occurring in the colonic lumen after ingestion of fibers and resveratrol-containing food.

New and better protocols for a short-term Caco-2 cell culture system

The aim of the present study was to develop new and better protocols for a short-term Caco-2 cell culture system for use in rapid screening of intestinal drug absorption. Caco-2 cells were cultured according to several protocols for short-term cell culture to obtain monolayers. The effects of serum (fetal bovine serum, FBS) in the culture medium and of the period of cell culture on the barrier function and transporter activities of the monolayers were examined. The barrier function was estimated both from the transepithelial electrical resistance (TEER) and the permeability of [(14)C]mannitol. Transporter activities were monitored by measuring the permeability of [(14)C]glycylsarcosine for oligopeptide transporter (PepT1) and of rhodamine 123 for P-glycoprotein (P-gp). Caco-2 monolayers obtained by 3-day culture in the BIOCOAT HTS Caco-2 Assay System, developed by Becton Dickinson Bioscience, showed much higher permeability to hydrophilic compounds, such as mannitol, compared with those obtained by the standard 21-day culture system, due to the leaky structure of cell junctions. The newly developed 3-day protocol, which includes 10% FBS in the culture medium during the first day of culture, markedly enhanced TEER and lowered mannitol permeability of the monolayers. This protocol allowed us to better determine the rank order of permeability of compounds, giving results equivalent to those in the 21-day culture system. The longer culture period gave tighter monolayers, and the maximum value of TEER was obtained with 5 days in culture. However, after 5 days in culture, the integrity of monolayers decreased gradually. The highest activities of transporters, PepT1 and P-gp, in monolayers were obtained at days 5 or 6 of culture by the new protocol with FBS-containing medium. These results indicate that by a simple modification of the short-term culture protocol, it is possible to obtain Caco-2 monolayers with better barrier properties and higher activity of transporters that are equivalent to those found in the 21-day Caco-2 culture system.

Calretinin and calretinin-22k increase resistance toward sodium butyrate-induced differentiation in CaCo-2 colon adenocarcinoma cells

Calretinin (CR) and the alternatively spliced form calretinin-22k (CR-22k) are members of the EF-hand family of Ca(2+)-binding proteins (CaBPs). CR is expressed in more than 60% of poorly differentiated human colon tumors and both isoforms are present in several colon carcinoma cell lines (e.g., WiDr). They are absent in normal enterocytes and in well-differentiated adenocarcinoma cell lines such as CaCo-2. Calretinins are thought to act as Ca(2+) buffers and to be involved in the regulation of Ca(2+)-dependent processes. Down-regulation of calretinins in WiDr cells by antisense oligonucleotides leads to growth inhibition and treatment with sodium butyrate (NaBt, an inducer of differentiation) leads to a blockage of the cell cycle and, in parallel, to down-regulation of CR. It has been proposed that CR and/or CR-22k may be involved in maintaining the undifferentiated phenotype of WiDr cells and contributing to the transformation of enterocytes. Expression levels and distribution of CR-22k were investigated in WiDr cells. CR-22k was down-regulated in NaBt-treated cells and the normally cytoplasmic protein was preferentially localized in the nucleus either as a result of translocation or selective nuclear maintenance, a process more pronounced than in the case of CR. To compare functional differences of calretinins, CR-negative Caco-2 cells were stably transfected with cDNAs encoding CR or CR-22k. Cell growth of CR-transfected cells was increased, an effect that was not observed in CR-22k-transfected ones. The CR-expressing clones were almost completely resistant to treatment with 0.5 mM NaBt, a concentration significantly reducing cell growth in control cells. The same effect was obtained in the CR-22k-expressing clones, although to a lesser extent. This implicates that expression of CR and/or CR-22k in colon tumor cells may contribute to tumorigenesis by blocking differentiation-promoting signals.

HMG-CoA reductase inhibitor mevastatin enhances the growth inhibitory effect of butyrate in the colorectal carcinoma cell line Caco-2

Mevastatin is an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, the rate-limiting enzyme in cholesterol synthesis. Butyrate, a short-chain fatty acid, reduces proliferation and induces differentiation of human colon cancer cells. The aim of our study was to determine the effect of mevastatin, alone or in combination with butyrate, on proliferation, the cell cycle and apoptosis in the human colorectal carcinoma cell line Caco-2. In this report we show that mevastatin combined with butyrate synergistically suppressed growth of Caco-2 cells in a dose- and time-dependent manner. In addition, incubation with mevastatin arrested cells in the G1 phase of the cell cycle after 24 h with a switch to the G2/M phase after 72 h. This was accompanied by a down-regulation of cyclin-dependent kinases (cdk) 4 and cdk 6 as well as cyclin D1, while cdk 2 and cyclin E protein levels remained unchanged during mevastatin treatment. Cell cycle inhibitors p21 and p27 were significantly upregulated by mevastatin. The proapoptotic properties of mevastatin were further enhanced by co-incubation with butyrate. Lastly, the effects of mevastatin could be reversed by addition of mevalonate, but not farnesyl- or geranylgeranylpyrophosphate, intermediate products of cholesterol synthesis, to the medium. These results suggest that HMG-CoA reductase inhibitors like mevastatin may enhance the antiproliferative effect of butyrate in colon cancer cells via induction of apoptosis together with a G0/G1 cell cycle arrest.

Alterations of MAPK activities associated with intestinal cell differentiation

Three distinct groups of mitogen-activated protein kinases (MAPKs) have been identified in mammalian cells (i.e., ERK, JNK, and p38) which play an important role in the differentiation and apoptosis of various cells. The purpose of our present study was to determine MAPK activity and levels associated with sodium butyrate (NaBT)-mediated differentiation and apoptosis in the human colon cancer cell lines Caco-2 and HT29. Intestinal alkaline phosphatase (IAP) activity, a marker of intestinal differentiation, was increased at 48 h after NaBT treatment followed by cell death at 72 h. ERK activity was decreased in differentiated Caco-2 cells either induced with NaBT or allowed to differentiate spontaneously and in HT29 cells treated with NaBT. The combination of the MEK inhibitor, PD98059, with NaBT further increased IAP activity and cell death compared with NaBT alone. In contrast to ERK, JNK1 activity and c-Jun phosphorylation was increased 8 h after NaBT treatment suggesting a role for the JNK pathway in intestinal cell differentiation and apoptosis. p38 activity was increased at 24 and 48 h after NaBT treatment. Taken together, our results suggest that alterations in MAPKs (i.e., ERK inhibition and JNK induction) contribute to the differentiation and apoptotic pathways in intestinal cells.

Butyrate-induced differentiation of Caco-2 cells occurs independently from p27

Butyrate, a short-chain fatty acid produced in the colon, reduces proliferation and increases differentiation of colon cancer cells. p27, an inhibitor of cyclin-dependent kinases and a negative regulator of the cell cycle, is thought to have a key function in the differentiation of various cell lines. The objective of the present study was to elucidate the role of p27 in butyrate-induced differentiation of the human colorectal carcinoma cell line Caco-2. In this report we show that in spite of the increase in p27 protein expression after incubation with the HMG-CoA reductase inhibitor mevastatin, alkaline phosphatase activity decreases significantly in this cell line. In addition, mevastatin caused a significant increase in the cell cycle inhibitor p21. All effects could be reversed by addition of mevalonate to the medium. Taken together, we provide the first evidence that in Caco-2 cells p27 may have other functions apart from the regulation of cell differentiation.

Integrin and FAK-mediated MAPK activation is required for cyclic strain mitogenic effects in Caco-2 cells

Rhythmic strain stimulates Caco-2 proliferation. We asked whether mitogen-activated protein kinase (MAPK) activation mediates strain mitogenicity and characterized upstream signals regulating MAPK. Caco-2 cells were subjected to strain on collagen I-precoated membranes or antibodies to integrin subunits. Twenty-four hours of cyclic strain increased cell numbers compared with static conditions. MAPK-extracellular signal-regulated kinase (ERK) kinase inhibition (20 microM PD-98059) blocked strain mitogenicity. p38 Inhibition (10 microM SB-202190) did not. Strain rapidly and time-dependently activated focal adhesion kinase (FAK), paxillin, ERK1 and 2, and p38 on collagen. c-Jun NH(2)-terminal kinase (JNK)1 and 2 exhibited delayed activation. Similar activation occurred when Caco-2 cells were subjected to strain on a substrate of functional antibody to the alpha2-, alpha3-, alpha6-, or beta1-integrin subunits but not on a substrate of functional antibody to the alpha5-subunit. FAK inhibition by FAK397 transfection blocked ERK2 and JNK1 activation by in vitro kinase assays, but pharmacological protein kinase C inhibition did not block ERK1 or 2 activation by strain. Strain-induced ERK signals mediate strain's mitogenic effects and may require integrins and FAK activation.

Identification and comparative analysis of human colonocyte short-chain fatty acid response genes

Short-chain fatty acids (SCFAs) butyrate, propionate, and acetate produced during fiber fermentation promote colonic differentiation and can reverse or suppress neoplastic progression. We sought to identify candidate genes responsible for SCFA activity on colonocytes and to compare the relative activities of independent SCFAs. cDNA was generated from polyA+ mRNA isolated from control Caco-2 cells and cells treated with equimolar butyrate, propionate, and acetate. GeneCalling, a restriction-based differential RNA expression platform linked to a DNA sequence database lookup, was applied. A total of 30,000 individual genetic sequences were analyzed for differential expression among the three SCFAs. Differentially expressed peaks corresponding to cancer-related genes were isolated, sequenced, and cross-referenced to the GenBank human database. Gene identities were independently confirmed by oligonucleotide poisoning. More than 1000 gene fragments were identified as being substantially modulated in expression by butyrate. Butyrate tended to have the most pronounced effects and acetate the least. Five fragments selected for further study were fully sequenced and proved 100% homologous with human sequences for clusterin, amyloid precursor-like protein 2, and caudal homeobox 2 protein, not previously known to be modulated by SCFAs. In each case, a similar order of potency for the three SCFAs studied was observed. The common SCFAs appear to exert different effects. This study suggests the diversity of the SCFA response at the molecular level and facilitates identifying genes important in the biologic activity of dietary fiber.

Association between the calcium-binding protein calretinin and cytoskeletal components in the human colon adenocarcinoma cell line WiDr

Calretinin (CR) is a Ca(2+)-binding protein (CaBP) of the EF-hand family expressed in a cell-type-specific manner and thought to act as a Ca(2+) buffer. Based upon previous studies, CR can undergo Ca(2+)-induced conformational changes, suggesting that it may also belong to the subfamily of Ca(2+)-sensor proteins that are characterized by their ability to interact with target ligands. To elucidate the role of CR, we used the undifferentiated colon adenocarcinoma cell line WiDr, which expresses significant amounts of CR. It has been shown previously that combined treatment with an inducer of differentiation sodium butyrate (NaBt) and a cell growth inhibitor hexamethylene bisacetamide (HMBA) or treatment with CR antisense oligonucleotides is down-regulating CR in parallel with a decrease of cell growth, suggesting a possible involvement of CR in maintaining the undifferentiated phenotype of WiDr cells. Furthermore, CR is absent from normal colon cells and from well-differentiated colon adenocarcinoma cell lines (e.g., Caco-2). Since members of the EF-hand family of proteins are interacting with cytoskeletal components, we investigated the possible association of CR with the cytoskeleton in WiDr cells. With double immunofluorescence stainings and immunoprecipitation experiments, we show close association of CR with intermediate filaments or microtubules in WiDr cells. Treatment with NaBt either disrupted or strongly diminished this interaction, respectively. The same effect was observed after elevation of [Ca(2+)](i) by applying the ionophore A-23187. These data suggest that CR may contribute to the transformation of enterocytes by interfering with the differentiation process, i.e., acting at both levels: cell shape dynamics and mitosis.

Redistribution of cyclic GMP in response to sodium butyrate in colon cells

The effect of butyrate on the response to guanylin and Escherichia coli heat-stable enterotoxin, STa, was assessed in T84 cells and Caco-2 cells, cultured colon cell lines possessing the guanylyl cyclase C which is the receptor for these peptides. Butyrate treatment of these cells resulted in an apparent increase in cyclic GMP (cGMP) accumulation when the cGMP content of cells and the supernatant medium was measured. Butyrate treatment did not change the guanylyl cyclase activity or (125)I-STa binding parameters in T84 cells, but the butyrate effect was completely blocked by cycloheximide. Butyrate did not have any effect on STa-stimulated cGMP accumulation in COS cells transfected with the human or porcine GC-C. Further experiments showed that butyrate treatment caused a large increase in the cGMP released into the culture medium, and in cells grown in polarized fashion in Transwell inserts, cGMP efflux was predominantly from the basolateral surface of the cell; intracellular cGMP was actually lowered by butyrate treatment. Exposure of T84 cells to butyrate had no effect on the disposition of cyclic AMP generated in response to forskolin. The effects of butyrate on cGMP were reversible within 24 h of butyrate withdrawal. In colon cells, butyrate treatment induced a previously undescribed, cGMP-specific efflux mechanism which lowered intracellular cGMP and elevated extracellular cGMP in response to peptide agonists such as guanylin and STa.

Dietary factors in human colorectal cancer

Colorectal cancer is a significant cause of mortality in Western societies. The progression of the disease from normal colonic epithelium to the acquisition of the malignant phenotype is accompanied by numerous genetic and epigenetic alterations. Compelling experimental and epidemiological evidence indicates that diet and nutrition are key factors in the modulation of colorectal cancer. A salient case in point is the recent observation that a dietary regimen based on a Western-style diet provokes in the rodent colon the appearance of preneoplastic lesions in the absence of any genotoxic insult. This review mainly describes dietary factors that inhibit the development and progression of colorectal cancer. Much is unknown about the precise mechanisms of action of chemically disparate nutrients and how they interfere with the development and progression of this disease. Current knowledge about this important issue is summarized. We believe that continuing scrutiny and precise assessment of the benefits (and potential risks) of nutrients in the treatment and prevention of colorectal cancer will prove significant to controlling this devastating disease.

Comparative effects of overexpression of p27Kip1 and p21Cip1/Waf1 on growth and differentiation in human colon carcinoma cells

Recent studies have shown that decreased expression of p27Kip1 is associated with high grade tumors and an unfavorable prognosis in several types of human cancer. To clarify the role of p27Kip1 in colon cancer, we have overexpressed this protein in the HT29 colon cancer cell line. The derivatives displayed an increase in the p27Kip1 protein in cyclin E/CDK2 immunoprecipitates and a decrease in cyclin E-associated kinase activity when compared to vector control clones, providing evidence that the overexpressed protein was functional. Clones with a high level of p27Kip1 displayed partial growth inhibition in monolayer culture and a decrease in plating efficiency, even though they expressed increased levels of the cyclin D1 protein. Using alkaline phosphatase expression as a marker, we found that the p27Kip1 overexpressor clones displayed a 2-3-fold increase in sensitivity to induction of differentiation by 2 mM sodium butyrate. In contrast to these results, derivatives of HT29 cells that stably overexpressed p21Cip1/Waf1 displayed decreased sensitivity to the induction of differentiation. These findings may explain why decreased levels of p27Kip1 in certain human cancers is associated with high grade (poorly differentiated) tumors, and suggest that strategies that increase the level of p27Kip1 may be useful in cancer therapy.

Short chain fatty acids inhibit human (SW1116) colon cancer cell invasion by reducing urokinase plasminogen activator activity and stimulating TIMP-1 and TIMP-2 activities, rather than via MMP modulation

BACKGROUND

Short chain fatty acids derived from dietary fiber may protect against invasive colon cancer by modulating degradative matrix metalloproteinases (MMPs) and protective tissue inhibitor matrix metalloproteinases (TIMPs). Since invasion depends on the MMP/TIMP ratio, we hypothesized that short chain fatty acids inhibit colon cancer invasion by inhibiting MMPs and stimulating TIMPs.

MATERIALS AND METHODS

SW1116 colon cancer cells were seeded onto Matrigel-coated Boyden chambers and treated with unsupplemented media or media containing 10 mM acetate, propionate, or butyrate. SW1116 invasion was quantitated by light microscopy and conditioned media were assayed by ELISA for MMP-1,2,3,9; TIMP-1,2; MMP/TIMP complex; and urokinase plasminogen activator (uPA). All data are expressed as mean percentage of control +/- SE (n > 6).

RESULTS

Although all three short chain fatty acids inhibited invasion, butyrate was more potent than either acetate or propionate, inhibiting SW1116 invasion by 35 +/- 1% of control (n = 18, P < .0001) vs. 18 +/- 9% (n = 7, P < .05) for acetate and 10 +/- 6% (n = 7, P < .05) for propionate. MMP-2 was not modulated by any of the short chain fatty acids while MMP-1 was modulated only by butyrate and MMP-3 by propionate. Acetate did not modulate MMPs, TIMP-1, or uPA, but stimulated TIMP-2. In contrast, propionate and butyrate stimulated MMP-9 and TIMP-2 by 119-233% and both inhibited uPA by 8-16%. TIMP-1 was stimulated only by butyrate and actually inhibited by propionate. Only butyrate stimulated both TIMP-1 and TIMP-2.

CONCLUSIONS

These data suggest that dietary fiber may protect against invasive colon cancer through stimulation of TIMP and inhibition of uPA activities, rather than through short chain fatty acids effects on the activities of the MMPs studied.

Effects of short-chain fatty acids on human rectosigmoid mucosal colonocyte brush-border enzymes

Short-chain fatty acids produced by bacterial fermentation of dietary fiber may provide a tonic stimulus to colonocyte differentiation that contributes to the protective effect of fiber against colorectal malignancy. Since brush-border enzymes are common markers of colonocytic differentiation, we compared the effects of equimolar (10 mmol/L) concentrations of the three most common short-chain fatty acids, acetate, butyrate, and propionate, on the alkaline phosphatase and dipeptidyl dipeptidase specific activity of human colonic mucosal biopsies obtained from normal volunteers. Only butyrate significantly stimulated alkaline phosphatase specific activity (50.4% +/- 18.6%, P < .05). Short-chain fatty acid stimulation of dipeptidyl dipeptidase did not achieve statistical significance. Fibers yielding high colonic butyrate levels could have different effects on human colonic mucosal differentiation.