Role of apoptosis in biology and pathology: resistance to apoptosis in colon carcinogenesis

Seaweed-Derived Sulfated Polysaccharides; The New Age Chemopreventives: A Comprehensive Review

Seaweed-derived bioactive compounds are regularly employed to treat human diseases. Sulfated polysaccharides are potent chemotherapeutic or chemopreventive medications since it has been discovered. They have exhibited anti-cancer properties by enhancing immunity and driving apoptosis. Through dynamic modulation of critical intracellular signalling pathways, such as control of ROS generation and preservation of essential cell survival and death processes, sulfated polysaccharides' antioxidant and immunomodulatory potentials contribute to their disease-preventive effectiveness. Sulfated polysaccharides provide low cytotoxicity and good efficacy therapeutic outcomes via dynamic modulation of apoptosis in cancer. Understanding how sulfated polysaccharides affect human cancer cells and their molecular involvement in cell death pathways will showcase a new way of chemoprevention. In this review, the significance of apoptosis and autophagy-modulating sulfated polysaccharides has been emphasized, as well as the future direction of enhanced nano-formulation for greater clinical efficacy. Moreover, this review focuses on the recent findings about the possible mechanisms of chemotherapeutic use of sulfated polysaccharides, their potential as anti-cancer drugs, and proposed mechanisms of action to drive apoptosis in diverse malignancies. Because of their unique physicochemical and biological properties, sulfated polysaccharides are ideal for their bioactive ingredients, which can improve function and application in disease. However, there is a gap in the literature regarding the physicochemical properties and functionalities of sulfated polysaccharides and the use of sulfated polysaccharide-based delivery systems in functional cancer. Furthermore, the preclinical and clinical trials will reveal the drug's efficacy in cancer.

Importance of Conjugation of the Bile Salt on the Mechanism of Lipolysis

We aim to advance the discussion on the significance of the conjugation of bile salts (BS) in our organism. We hypothesize that conjugation influences the rate of lipolysis. Since the rate of lipolysis is a compound parameter, we compare the effect of conjugation on four surface parameters, which contribute to the rate. Since deconjugation is due to gut microbiota, we hypothesize that microbiota may affect the rate of lipolysis. A meta-analysis of literature data of critical micelle concentration, β, aggregation number, and molar solubilization ratio has been performed for the first time. In addition, critical micelle concentration (CMC), interfacial tension, and lipolysis rate measurements were performed. It was found that the unconjugated BS in mixed micelles increases the antagonism between the BS, therefore, increasing the CMC. This correlated with the effect of unconjugated BS on the solubilization capacity of mixed micelles. The collected literature information indicates that the role of the BS and its conjugation in our organism is a key factor influencing the functioning of our organism, where too high levels of unconjugated BS may lead to malabsorption of fat-soluble nutrients. The experimental lipolysis results irrevocably showed that conjugation is a significant factor influencing the rate.

Pharmacophore-based identification and in vitro validation of apoptosis inducers as anticancer agents

Ligand-based pharmacophore modelling and virtual screening along with in vitro screening were performed as a rational strategy for the identification of novel compounds as apoptosis inducers and anticancer agents from the chemical database. Known apoptosis inducers were selected from the literature for generation of pharmacophore models, which were subjected to validation using Receiver operating characteristic (ROC) and Günere-Henry (GH) scoring methods. Based on highest fitness score of 4680.61, ROC value of 0.872 and GH score of 0.758, pharmacophore model-2 was selected as the best model. Model-2 as 3D search query was searched against the IBS database to find novel compounds as hits. Three hits were selected with a Q_FIT value more than 82 for in vitro screening as apoptosis inducers and anticancer agents. In vitro anticancer activity was performed using resazurin cell variability assay, and apoptosis inducing activity was determined using caspase-3 activation and annexin-FITC assays. One of the retrieved hit, STOCK5S-44056 demonstrated IC₅₀ value of 23.56 µM in cell variability assay, and had EC₅₀ value of 26.95 µM in caspase-3 activation assay. STOCK5S-44056 also indicated late stage induction of apoptosis in annexin assay. The results of in vitro activity revealed that STOCK5S-44056 has a potential to become anticancer agents.

The Effect of Microbiota on Colon Carcinogenesis

Although genetic background is known to contribute to colon carcinogenesis, the exact etiology of the disease remains elusive. The organ’s extensive interaction with microbes necessitated research on the role of microbiota on development of colon cancer. In this review, we summarized the defense mechanism of colon from foreign organism, and germ-free animal models that have been employed to elucidate microbial effect. We also comprehensively discussed the metabolic property of microbiota such as butyrate production, facilitation of heme toxicity, bile acid transformation, and nitrate reduction that has been shown to contribute to the development of the tumor. Finally, up-to-date subjects such as the effect of age and gender on microbiota are briefly discussed.

Fecal Metabolome in Hmga1 Transgenic Mice with Polyposis: Evidence for Potential Screen for Early Detection of Precursor Lesions in Colorectal Cancer

Because colorectal cancer (CRC) remains a leading cause of cancer mortality worldwide, more accessible screening tests are urgently needed to identify early stage lesions. We hypothesized that highly sensitive, metabolic profile analysis of stool samples will identify metabolites associated with early stage lesions and could serve as a noninvasive screening test. We therefore applied traveling wave ion mobility mass spectrometry (TWIMMS) coupled with ultraperformance liquid chromatography (UPLC) to investigate metabolic aberrations in stool samples in a transgenic model of premalignant polyposis aberrantly expressing the gene encoding the high mobility group A (Hmga1) chromatin remodeling protein. Here, we report for the first time that the fecal metabolome of Hmga1 mice is distinct from that of control mice and includes metabolites previously identified in human CRC. Significant alterations were observed in fatty acid metabolites and metabolites associated with bile acids (hypoxanthine xanthine, taurine) in Hmga1 mice compared to controls. Surprisingly, a marked increase in the levels of distinctive short, arginine-enriched, tetra-peptide fragments was observed in the transgenic mice. Together these findings suggest that specific metabolites are associated with Hmga1-induced polyposis and abnormal proliferation in intestinal epithelium. Although further studies are needed, these data provide a compelling rationale to develop fecal metabolomic analysis as a noninvasive screening tool to detect early precursor lesions to CRC in humans.

Stromal COX-2 signaling are correlated with colorectal cancer: A review

Cyclooxygenase-2 (COX-2) and its product prostaglandin E₂ (PGE₂) play a critical role in development and progression of colorectal cancer. Yet the detailed mechanistic pathways of COX-2 mediated signaling are still controversial and the role of COX-2 interaction in epithelial-stromal compartments on colorectal carcinogenesis is not well-understood either. In this review, we provide experimental evidence to support that (1) COX-2 signaling plays a major role in development and progression of colorectal cancer; (2) Stromal fibroblasts are a major source of COX-2 and PGE₂; (3) Stromal-epithelial interaction mediated by COX-2 signaling promotes colorectal carcinogenesis and (4) Inhibition of stromal COX-2 signaling is necessary to control colorectal cancer. In conclusion, the evidences summarized in the review reflect recent advances and insight in mechanistic studies of colorectal cancer which can help the audiences to further understand the etiology and the control of this disease.

The short appendix vermiformis as a risk factor for colorectal cancer

The human appendix vermiformis is regarded as an evolutionarily vestigial organ, although it has presumptive immune system functions and appears to support beneficial bacterial gut flora, both of which could influence cancer progression. A review of the comparative anatomy of the mammalian appendix reveals a significantly longer appendix in herbivores than in carnivorous animals. The lengthier appendix vermiformis in herbivores has been associated with the presence of cellulose-digesting bacteria that colonize the structure. In light of recent studies that have reported the digestion of small amounts of cellulose in humans and the preventive effects of a vegetarian diet on colon cancer, we conducted a retrospective study of abdominal CT scans of 60 colon cancer patients and 60 healthy people to investigate a possible relationship between colon cancer and appendix vermiformis length. The mean length of the appendix in cancer patients [65.178 mm ± 13.46 (SD)] was shorter than that in the healthy control group [101.99 mm ± 16.58 (SD)] and the difference was statistically significant (P < 0.001). Statistical analysis demonstrated that the ages of the cancer patient group and the control group did not differ significantly (P = 0.534). The results of the present study indicate that the appendix is not merely a vestigial structure or regressed lymphoid tissue, but rather an organ that could be critical in the development of colon cancer, whether as a result of congenital or acquired appendicular factors.

The Prevalence and Importance of Crypt Apoptosis, Focal Active Cryptitis, and Neutrophilic Infiltrate of the Lamina Propria in Colorectal Adenomas

Even though apoptotic bodies (ABs) are frequent in colorectal adenomas, their relevance has been covered only in a few studies. Focal active cryptitis (FAC) is a well-known manifestation of several etiologies; however, its prevalence and significance in colonic adenomas were not scrutinized. Likewise, whether the neutrophilic infiltrate of the lamina propria (LP) in colonic adenomas has a clinical or pathologic significance was not previously studied. We attempted to investigate the prevalence and importance of ABs in the cryptal epithelium and of neutrophils in the form of FAC and in the form of LP infiltrates in conventional colorectal adenomas. We conducted a retrospective review study over a 6-year period. We collected 223 conventional adenomas from 156 patients. We studied the interrelationship between these 3 histologic parameters and their potential association with other clinical and pathologic variables. Comparison controls included normal colonic mucosa, hyperplastic polyps, serrated adenomas, and flat adenomas. We found 91 (41%) adenomas to have crypt apoptosis, 40 (18%) to have FAC, and 69 (31%) to have neutrophilic infiltrate of the LP. We found ABs to be more frequent in high-grade adenomas. LP neutrophilic infiltrate was significantly associated with high-grade adenomas and in high-grade adenomas with invasive foci. In contrast, FAC was not associated with high-grade adenomas and was secondary to bowel preparations and drugs. Crypt apoptosis and LP neutrophils might have a potential prognostic value in predicting the biologic behavior of colonic adenomas. FAC in adenomas is a nonspecific finding of no prognostic significance and is related to external stimuli.

Bile acids in the colon, from healthy to cytotoxic molecules

Bile acids are natural detergents mainly involved in facilitating the absorption of dietary fat in the intestine. In addition to this absorptive function, bile acids are also essential in the maintenance of the intestinal epithelium homeostasis. To accomplish this regulatory function, bile acids may induce programmed cell death fostering the renewal of the epithelium. Here we first discuss on the different molecular pathways of cell death focusing on apoptosis in colon epithelial cells. Bile acids may induce apoptosis in colonocytes through different mechanisms. In contrast to hepatocytes, the extrinsic apoptotic pathway seems to have a low relevance regarding bile acid cytotoxicity in the colon. On the contrary, these molecules mainly trigger apoptosis through direct or indirect mitochondrial perturbations, where oxidative stress plays a key role. In addition, bile acids may also act as regulatory molecules involved in different cell signaling pathways in colon cells. On the other hand, there is increasing evidence that the continuous exposure to certain hydrophobic bile acids, due to a fat-rich diet or pathological conditions, may induce oxidative DNA damage that, in turn, may lead to colorectal carcinogenesis as a consequence of the appearance of cell populations resistant to bile acid-induced apoptosis. Finally, some bile acids, such as UDCA, or low concentrations of hydrophobic bile acids, can protect colon cells against apoptosis induced by high concentrations of cytotoxic bile acids, suggesting a dual behavior of these agents as pro-death or pro-survival molecules.

Maspin is a deoxycholate-inducible, anti-apoptotic stress-response protein differentially expressed during colon carcinogenesis

Increased maspin expression in the colon is related to colon cancer risk and patient survival. Maspin is induced by the hydrophobic bile acid, deoxycholate (DOC), which is an endogenous carcinogen and inducer of oxidative stress and DNA damage in the colon. Persistent exposure of colon epithelial cells, in vitro, to high physiologic levels of DOC results in increased constitutive levels of maspin protein expression associated with the development of apoptosis resistance. When an apoptosis-resistant colon epithelial cell line (HCT-116RC) developed in the authors' laboratory was treated with a maspin-specific siRNA probe, there was a statistically significant increase in apoptosis compared to treatment with an siRNA control probe. These results indicate, for the first time, that maspin is an anti-apoptotic protein in the colon. Immunohistochemical evaluation of maspin expression in human colonic epithelial cells during sporadic colon carcinogenesis (131 human tissues evaluated) indicated a statistically significant increase in maspin protein expression beginning at the polyp stage of carcinogenesis. There was no statistically significant difference in maspin expression between hyperplastic/adenomatous polyps and colonic adenocarcinomas. The absence of "field defects" in the non-neoplastic colonic mucosa of patients with colonic neoplasia indicates that maspin may drive the growth of tumors, in part, through its anti-apoptotic function.

The Na+/H+ exchanger controls deoxycholic acid-induced apoptosis by a H+-activated, Na+-dependent ionic shift in esophageal cells

Apoptosis resistance is a hallmark of cancer cells. Typically, bile acids induce apoptosis. However during gastrointestinal (GI) tumorigenesis the cancer cells develop resistance to bile acid-induced cell death. To understand how bile acids induce apoptosis resistance we first need to identify the molecular pathways that initiate apoptosis in response to bile acid exposure. In this study we examined the mechanism of deoxycholic acid (DCA)-induced apoptosis, specifically the role of Na⁺/H⁺ exchanger (NHE) and Na⁺ influx in esophageal cells. In vitro studies revealed that the exposure of esophageal cells (JH-EsoAd1, CP-A) to DCA (0.2 mM -0.5 mM) caused lysosomal membrane perturbation and transient cytoplasmic acidification. Fluorescence microscopy in conjunction with atomic absorption spectrophotometry demonstrated that this effect on lysosomes correlated with influx of Na⁺, subsequent loss of intracellular K⁺, an increase of Ca²⁺ and apoptosis. However, ethylisopropyl-amiloride (EIPA), a selective inhibitor of NHE, prevented Na⁺, K⁺ and Ca²⁺ changes and caspase 3/7 activation induced by DCA. Ouabain and amphotericin B, two drugs that increase intracellular Na⁺ levels, induced similar changes as DCA (ion imbalance, caspase3/7 activation). On the contrary, DCA-induced cell death was inhibited by medium with low a Na⁺ concentrations. In the same experiments, we exposed rat ileum ex-vivo to DCA with or without EIPA. Severe tissue damage and caspase-3 activation was observed after DCA treatment, but EIPA almost fully prevented this response. In summary, NHE-mediated Na⁺ influx is a critical step leading to DCA-induced apoptosis. Cells tolerate acidification but evade DCA-induced apoptosis if NHE is inhibited. Our data suggests that suppression of NHE by endogenous or exogenous inhibitors may lead to apoptosis resistance during GI tumorigenesis.

Carcinogenicity of deoxycholate, a secondary bile acid

High dietary fat causes increased bile acid secretion into the gastrointestinal tract and is associated with colon cancer. Since the bile acid deoxycholic acid (DOC) is suggested to be important in colon cancer etiology, this study investigated whether DOC, at a high physiologic level, could be a colon carcinogen. Addition of 0.2% DOC for 8-10 months to the diet of 18 wild-type mice induced colonic tumors in 17 mice, including 10 with cancers. Addition of the antioxidant chlorogenic acid at 0.007% to the DOC-supplemented diet significantly reduced tumor formation. These results indicate that a high fat diet in humans, associated with increased risk of colon cancer, may have its carcinogenic potential mediated through the action of bile acids, and that some dietary anti-oxidants may ameliorate this carcinogenicity.

Hydrophobic bile acid-induced micronuclei formation, mitotic perturbations, and decreases in spindle checkpoint proteins: relevance to genomic instability in colon carcinogenesis

We show, for the first time, that hydrophobic bile acids cause aberrations of the mitotic machinery of colon cells that can give rise to aneuploidy, the chromosomal perturbations common in colon tumors. First, we show that DOC induces a statistically significant fourfold increase in the number of micronuclei in NCM-460 cells (a noncancerous colon cell line) and a threefold increase in the number of micronuclei in binucleated HT-29 colon cancer cells using the cytokinesis block micronucleus assay. Second, we observed mitotic aberrations after DOC treatment, including improper alignment of chromosomes at the metaphase plate, lagging chromosomes during anaphase, anaphase/telophase chromatin bridges, multipolar divisions, and formation of polynucleated cells. It was determined that there was a statistically significant threefold increase in the number of aberrant metaphases after short-term and long-term exposure of HT-29 and HCT-116 cells, respectively. Third, we showed with Western blots and immunohistochemistry that a likely basis for these mitosis-related perturbations included decreased expression of the spindle checkpoint proteins, Mad2, BubR1, and securin. Fourth, results of DOC treatment on nocodazole-challenged cells further indicated deficiencies in activation of the spindle assembly checkpoint. This study provides mechanisms by which hydrophobic bile acids can induce genomic instability in colon epithelial cells.

Metastasis-associated genes in oral squamous cell carcinoma and salivary adenoid cystic carcinoma: a differential DNA chip analysis between metastatic and nonmetastatic cell systems

Overall modes of differential gene expressions were analyzed between human oral/salivary carcinoma cell systems with (MK-1 and ACCM) and without (ZK-1/ZK-2 and ACC2/ACC3) metastatic potential by using micro-array analysis with cancer-associated DNA chips to determine the kinds of genes associated with metastatic behaviors. MK-1 and/or ACCM showed lower levels of gene expression in extracellular matrix-related molecules, such as collagen type IV, laminin, and adhesion molecules such as cadherin 2, but higher levels of genes which control extracellular matrix degradation, such as MMP 9, as well as cell growth and cycle, such as FGF7 and cyclin D1. Among the differentially expressed genes, similar protein expression tendencies for FGF7, laminin, cyclin D1, and collagen type IV were confirmed by immunofluorescence. Metastatic potentials of oral/salivary carcinoma cells seem to have resulted from certain combinations of over-/underexpression of the genes, which were responsible for extracellular matrix metabolism and cell growth in particular.

Bile acids as endogenous etiologic agents in gastrointestinal cancer

Bile acids are implicated as etiologic agents in cancer of the gastrointestinal (GI) tract, including cancer of the esophagus, stomach, small intestine, liver, biliary tract, pancreas and colon/rectum. Deleterious effects of bile acid exposure, likely related to carcinogenesis, include: induction of reactive oxygen and reactive nitrogen species; induction of DNA damage; stimulation of mutation; induction of apoptosis in the short term, and selection for apoptosis resistance in the long term. These deleterious effects have, so far, been reported most consistently in relation to esophageal and colorectal cancer, but also to some extent in relation to cancer of other organs. In addition, evidence is reviewed for an association of increased bile acid exposure with cancer risk in human populations, in specific human genetic conditions, and in animal experiments. A model for the role of bile acids in GI carcinogenesis is presented from a Darwinian perspective that offers an explanation for how the observed effects of bile acids on cells contribute to cancer development.

Physical activity as a determinant of fecal bile acid levels

Physical activity is protective against colon cancer, whereas colonic bile acid exposure is a suspected risk factor. Although likely related, the association between physical activity and bile acid levels has not been well-studied. Furthermore, the effect of triglycerides, which are known to modify bile acid levels, on this relationship has not been investigated. We conducted a cross-sectional analysis of baseline fecal bile acid levels for 735 colorectal adenoma formers obtained from participants in a phase III ursodeoxycholic acid chemoprevention trial. Compared with the lowest quartile of recreational physical activity duration, the highest quartile was associated with a 17% lower fecal bile acid concentration, adjusted for age, sex, dietary fiber intake, and body mass index (P = 0.042). Furthermore, consistent with a previously established relationship between serum triglyceride levels and bile acid metabolism, we stratified by triglyceride level and observed a 34% lower fecal bile acid concentration (highest versus lowest quartiles of physical activity) in individuals with low triglycerides (<136 mg/dL; P = 0.002). In contrast, no association between physical activity and fecal bile acid concentration was observed for subjects with high triglycerides (> or =136 mg/dL). Our results suggest that the biological mechanism responsible for the protective effect of physical activity on the incidence of colon cancer may be partially mediated by decreasing colonic bile acid exposure. However, this effect may be limited to individuals with lower triglyceride levels.

Hydrophobic bile acids, genomic instability, Darwinian selection, and colon carcinogenesis

Sporadic colon cancer is caused predominantly by dietary factors. We have selected bile acids as a focus of this review since high levels of hydrophobic bile acids accompany a Western-style diet, and play a key role in colon carcinogenesis. We describe how bile acid-induced stresses cause cell death in susceptible cells, contribute to genomic instability in surviving cells, impose Darwinian selection on survivors and enhance initiation and progression to colon cancer. The most likely major mechanisms by which hydrophobic bile acids induce stresses on cells (DNA damage, endoplasmic reticulum stress, mitochondrial damage) are described. Persistent exposure of colon epithelial cells to hydrophobic bile acids can result in the activation of pro-survival stress-response pathways, and the modulation of numerous genes/proteins associated with chromosome maintenance and mitosis. The multiple mechanisms by which hydrophobic bile acids contribute to genomic instability are discussed, and include oxidative DNA damage, p53 and other mutations, micronuclei formation and aneuploidy. Since bile acids and oxidative stress decrease DNA repair proteins, an increase in DNA damage and increased genomic instability through this mechanism is also described. This review provides a mechanistic explanation for the important link between a Western-style diet and associated increased levels of colon cancer.

Field defects in progression to gastrointestinal tract cancers

A field of defective tissue may represent a pre-malignant stage in progression to many cancers. However, field defects are often overlooked in studies of cancer progression through assuming tissue at some distance from the cancer is normal. We indicate, however, the generality of field defects in gastrointestinal cancers, including cancers of the oropharynx, esophagus, stomach, bile duct, pancreas, small intestine and colon/rectum. Common features of these field defects are reduced apoptosis competence, aberrant proliferation and genomic instability. These features are often associated with high bile acid exposure and may explain the association of dietary-related factors with cancer progression.

Activation of the interleukin-6/STAT3 antiapoptotic pathway in esophageal cells by bile acids and low pH: relevance to barrett's esophagus

OBJECTIVES

The molecular factors contributing to the development of Barrett's esophagus (BE) are unclear. Our previous studies showed that BE tissues secrete interleukin-6 (IL-6) and express proteins associated with IL-6 signaling, including IL-6 receptor, activated signal transducer and activators of transcription 3 (STAT3), and antiapoptotic proteins Bcl-x(L) and Mcl-1. Here, we test the hypothesis that bile acids and gastric acids, two components of refluxate associated with gastresophageal reflux disease, activate the IL-6/STAT3 pathway.

MATERIALS AND METHODS

Immunohistochemistry was used to assess levels of phosphorylated STAT3 in esophageal tissue samples from BE patients with different grades of dysplasia. Seg-1 esophageal adenocarcinoma cells were evaluated for STAT3 activation and IL-6 and Bcl-x(L) expression by molecular biology techniques, including Western blot, reverse transcription-PCR, and ELISA after exposure to control media (pH 7.4), media supplemented with a 0.1 mmol/L bile acid cocktail with media at pH 4 or media at pH 4 with bile acid cocktail.

RESULTS

Immunohistochemical analysis showed that activated, phosphorylated STAT3 is expressed in nuclei of dysplastic BE and cancer tissues. Treatment of Seg-1 cells with media containing bile acid cocktail and acidified to pH 4 resulted in increased activation of STAT3, IL-6 secretion, and increased expression of Bcl-x(L). Inhibition of the STAT3 pathway using STAT3 small interfering RNA or Janus-activated kinase inhibitor resulted in increased apoptosis.

CONCLUSIONS

The IL-6/STAT3 antiapoptotic pathway is induced by short exposure to bile acid cocktail and low pH. This alteration, if persistent in vivo, may underlie the development of dysplastic BE and tumor progression.

Reduced Pms2 expression in non-neoplastic flat mucosa from patients with colon cancer correlates with reduced apoptosis competence

Pms2 protein is a component of the DNA mismatch repair complex responsible both for post-replication correction of DNA nucleotide mispairs and for early steps in apoptosis. Germline mutations in DNA mismatch repair genes give rise to hereditary non-polyposis colon cancer, which accounts for about 4% of colon cancers. However, little is known about the expression of mismatch repair proteins in relation to sporadic colon cancer, which accounts for the great majority of colon cancers. Multiple samples were taken from the non-neoplastic flat mucosa of colon resections from patients with no colonic neoplasia, a tubulovillous adenoma, or an adenocarcinoma. Expression of Pms2 was assessed using semiquantitative immunohistochemistry. Apoptosis was assessed in polychrome-stained epoxy sections using morphologic criteria. Samples from patients without colonic neoplasia had moderate to strong staining for Pms2 in cell nuclei at the base of crypts, while samples from 2 of the 3 colons with a tubulovillous adenoma, and from 6 of the 10 colons with adenocarcinomas, showed reduced Pms2 expression. Samples from patients with an adenocarcinoma that had reduced Pms2 expression also exhibited reduced apoptosis capability in nearby tissue samples, evidenced when this paired tissue was stressed ex vivo with bile acid. Reduced Pms2 expression in the colonic mucosa may be an early step in progression to colon cancer. This reduction may cause decreased mismatch repair, increased genetic instability, and/or reduced apoptotic capability. Immunohistochemical determination of reduced Pms2 expression, upon further testing, may prove to be a promising early biomarker of risk of progression to malignancy.

Ursodeoxycholic acid modulates histone acetylation and induces differentiation and senescence

Agents that can modulate colonic environment and control dysregulated signaling are being evaluated for their chemopreventive potential in colon cancer. Ursodeoxycholate (UDCA) has shown chemopreventive potential in preclinical and animal models of colon cancer, but the mechanism behind it remains unknown. Here biological effects of UDCA were examined to understand mechanism behind its chemoprevention in colon cancer. Our data suggests that UDCA can suppress growth in a wide variety of cancer cell lines and can induce low level of apoptosis in colon cancer cells. We also found that UDCA treatment induces alteration in morphology, increased cell size, upregulation of cytokeratin 8, 18 and 19 and E-cadherin, cytokeratin remodeling and accumulation of lipid droplets, suggesting that UDCA induces differentiation in colon carcinoma cells. Our results also suggest significant differences in UDCA and sodium butyrate induced functional differentiation. We also report for the first time that UDCA can induce senescence in colon cancer cells as assessed by flattened, spread out and vacuolated morphology as well as by senescence marker beta-galactosidase staining. We also found that UDCA inhibits the telomerase activity. Surprisingly, we found that UDCA is not a histone deacytylase inhibitor but instead induces hypoacetylation of histones unlike hyperacetylation induced by sodium butyrate. Our results also suggest that, although UDCA induced senescence is p53, p21 and Rb independent, HDAC6 appears to be important in UDCA induced senescence. In summary, our data shows that UDCA modulates chromatin by inducing histone hypoacetylation and induces differentiation and senescence in colon cancer cells.

Mitochondrial perturbation attenuates bile acid-induced cytotoxicity

Hydrophobic bile acids such as deoxycholate (DOC) are known to damage liver cells during cholestasis and promote colon cancer. Cellular stresses induced by bile acids, which include mitochondrial and endoplasmic reticulum (ER) stresses, can result in apoptosis. We found that inhibition of mitochondrial complexes I-V with rotenone, thenoyltrifluoroacetone (TTFA), antimycin A, myxothiazol or oligomycin strongly protected against DOC-induced apoptosis of HCT-116 cells. To understand the mechanism of this protection, we explored the ability of these specific inhibitors to reduce DOC-induced mitochondrial and ER stresses. Different inhibitors markedly reduced DOC-induction of mitochondrial condensation, the DOC-induced decrease in mitochondrial membrane potential and the DOC-induced dilatation of the ER (evidence of ER stress). A dramatic induction of nucleolar segregation by antimycin A and myxothiazol, two distinct complex III inhibitors, was also observed. These findings strongly implicate mitochondrial crosstalk with apoptotic signaling pathways and mitochondrial-nucleolar crosstalk in the development of apoptosis resistance in the colon.

Crypt-restricted loss and decreased protein expression of cytochrome C oxidase subunit I as potential hypothesis-driven biomarkers of colon cancer risk

There is an increasing demand for the development of intermediate biomarkers to assess colon cancer risk. We previously determined that a live cell bioassay, which assesses apoptosis resistance in the nonneoplastic colonic mucosa, detects approximately 50% of patients with colon cancer. A hypothesis-driven biomarker that reflects apoptosis resistance in routine formalin-fixed, paraffin-embedded tissue would be easier to use. Cytochrome c oxidase is a critical enzyme that controls mitochondrial respiration and is central to apoptosis. We did an immunohistochemical study of cytochrome c oxidase subunit I expression in 46 colonic mucosal samples from 16 patients who had undergone a colonic resection. These included five patients without evidence of colonic neoplasia (three normal and two diverticulitis), three patients with tubulovillous adenomas, and eight patients with colonic adenocarcinomas. Analysis of aberrancies in expression of cytochrome c oxidase subunit I showed that, compared with nonneoplasia, the patients with neoplasia had a higher mean incidence of crypts having decreased expression (1.7 versus 22.8, P = 0.03) and a higher mean incidence having crypt-restricted loss (0.6 versus 3.2, P = 0.06). The percentage with segmented loss was low and was similar in the two groups. Combining these results, the mean % normal (i.e., with none of the three types of abnormality) was 96.7 in nonneoplasia versus only 73.2 in patients with neoplasia (P = 0.02). It should be noted that a defect in cytochrome c oxidase subunit I immunostaining was not detected in all biopsy samples from each patient for whom some abnormality was found, indicating a "patchiness" in the cytochrome c oxidase subunit I field defect. As a result of this "patchiness," the increased variability in the incidence of crypt-restricted loss of cytochrome c oxidase subunit I expression was a statistically significant feature of the neoplasia group. Crypt-restricted loss of cytochrome c oxidase subunit I has not been previously reported in colonic mucosa and is presumably the result of a crypt-restricted stem cell mutation. Decreased cytochrome c oxidase subunit I expression also significantly correlated with apoptosis resistance, a factor known to contribute to carcinogenesis. The results suggest, however, that aberrant cytochrome c oxidase subunit I expression may be a better biomarker than loss of apoptosis competence for increased colon cancer risk.

Effect of Bile Acids on Butyrate-Sensitive and -Resistant Human Colon Adenocarcinoma Cells

A controlled balance among cell proliferation, differentiation, and apoptosis is required for the maintenance of gastrointestinal mucosa; these processes are influenced by luminal components, such as butyrate and bile acids. Using butyrate-sensitive (BCS-TC2) and butyrate-resistant (BCS-TC2.BR2) human colon carcinoma cells, we wanted to establish whether colon carcinoma cells that acquire resistance to butyrate-induced apoptosis are also resistant to the cytotoxic effect of certain bile acids, contributing, in this way, to the progression of colon carcinogenesis. The effect of bile acids on BCS-TC2 cell viability is dose and time dependent and highly stereospecific. Quantification of the relative percentage of apoptotic cells and caspase-3 activity reveals that deoxycholic acid (DCA) and chenodeoxycholic acid (CDCA) induce apoptosis in BCS-TC2 cells. BCS-TC2.BR2 cells are consistently less sensitive to their cytotoxic effects, requiring concentrations to induce 50% inhibition (IC50) in cell viability of 740 microM and >1 mM for CDCA and DCA, respectively, compared with IC50 values of 310 and 540 microM for BCS-TC2 cells. DCA-treated BCS-TC2.BR2 cells show few apoptotic signs and no caspase-3 activation. On the other hand, CDCA-treated BCS-TC2.BR2 cells show caspase-3 activation and apoptotic features, although to a lower extent than BCS-TC2 cells. Our results, in an in vitro model system, point out that acquisition of butyrate resistance is accompanied by a partial resistance to the cytotoxic effects of bile acids, which may enhance the survival of tumorigenic cells.

Bile acid induces hydrophobicity-dependent membrane alterations

Elevated concentrations of fecal bile acids are a known risk factor for colon cancer, owing to alterations in cellular signaling. In colonic cells, where bile acid uptake is minimal, the hydrophobicity-induced membrane perturbation and alterations have been proposed, but these membrane alterations are largely uncharacterized. In this study, we examined the determinants and characteristics of bile acid-induced membrane alterations, utilizing PKCalpha activation and cholesterol up-regulation as model indicators. We found that bile acid-induced PKCalpha activation is a function of hydrophobicity and correlated with alteration in membrane lipid composition, as evident by the significant up-regulation in membrane cholesterol and phospholipid. We found that bile acid do not cause cell membrane disruption at a concentration sufficient to activate PKCalpha, but do induce drastic alterations in membrane composition. Bile acid also induced the modification and up-regulation of caveolin-1 in a hydrophobicity-dependent manner, implying widespread receptor dysregulation. Similarly, ERK1/2 activation was observed only in response to hydrophobic bile acids, suggesting hydrophobicity-induced caveolar or membrane stress. Experiments with sodium lauryl sarcosine and cholesteryl hemisuccinate showed that bile acid-induced membrane alterations can be mimicked by hydrophobic molecules unrelated to bile acids, strongly implicating hydrophobicity as an important determinant of bile acid signaling.

Alteration of gene expression in macroscopically normal colonic mucosa from individuals with a family history of sporadic colon cancer

PURPOSE

We have shown that the expression of several genes associated with human colon cancer is altered in the morphologically normal colonic mucosa (MNCM) of APC(min) mice and humans with colon cancers. To determine whether these alterations also occur in the MNCM of individuals who have not developed colon cancer but are at high risk of doing so, we measured gene expression in the MNCM of individuals with a family history of colon cancer.

METHODS

Expression of 16 genes in the MNCM of 12 individuals with a first-degree relative with sporadic colon cancer and 16 normal controls were measured by quantitative reverse transcription-PCR. All subjects tested had normal colonoscopic examinations. Biopsy samples of MNCM were obtained from the ascending, transverse, descending, and rectosigmoid regions of the colon (2-8 biopsy samples were obtained from each region).

RESULTS

Relative to normal controls, the expression of several genes, including PPAR-gamma, SAA1, and IL-8 were significantly altered in the macroscopically normal rectosigmoid mucosa from individuals with a family history of colon cancer.

CONCLUSIONS

Molecular abnormalities that precede the appearance of adenomatous polyp are present in the MNCM of individuals who have a family history of colon cancer. This observation raises the possibility of screening for individuals who are at an increased risk of developing colon cancer by analysis of gene expression in rectosigmoid biopsy samples. To assess this possibility, prospective studies will be needed to determine whether or not altered gene expression is associated with the subsequent development of adenomatous polyps and/ or colonic carcinomas.

Bile acids as carcinogens in human gastrointestinal cancers

Bile acids were first proposed to be carcinogens in 1939 and 1940. On the basis of later work with rodent models, bile acids came to be regarded as cancer promoters rather than carcinogens. However, considerable indirect evidence, obtained more recently, supports the view that bile acids are carcinogens in humans. At least 15 reports, from 1980 through 2003, indicate that bile acids cause DNA damage. The mechanism is probably indirect, involving induction of oxidative stress and production of reactive oxygen species that then damage DNA. Repeated DNA damage likely increases the mutation rate, including the mutation rate of tumor suppressor genes and oncogenes. Additional reports, from 1994 through 2002, indicate that bile acids, at the increased concentrations accompanying a high fat diet, induce frequent apoptosis. Those cells within the exposed population with reduced apoptosis capability tend to survive and selectively proliferate. That bile acids cause DNA damage and may select for apoptosis-resistant cells (both leading to increased mutation), indicates that bile acids are likely carcinogens. In humans, an increased incidence of cancer of the laryngopharyngeal tract, esophagus, stomach, pancreas, the small intestine (near the Ampulla of Vater) and the colon are associated with high levels of bile acids. The much larger number of cell generations in the colonic (and, likely, other gastrointestinal) epithelia of humans compared to rodents may allow time for induction and selection of mutations leading to cancer in humans, although not in rodents.

Assessment of apoptosis by immunohistochemical markers compared to cellular morphology in ex vivo-stressed colonic mucosa

Apoptosis competence is central to the prevention of cancer. Frequency of apoptotic cells, after a sample of colonic tissue is stressed, can be used to gauge apoptosis competence and, thus, possible susceptibility to colon cancer. The gold standard for assessment of apoptosis is morphological evaluation, but this requires an experienced microscopist. Easier-to-use immunohistochemical markers of apoptosis, applicable in archived paraffin-embedded tissue, have been commercially developed. Potentially useful apoptosis markers include cleaved cytokeratin-18 (c-CK18), cleaved caspase-3 (c-cas-3), cleaved lamin A (c-lam-A), phosphorylated histone H2AX (gammaH2AX), cleaved poly(ADP ribose) polymerase (c-PARP), and translocation of apoptosis-inducing factor (AIF). When tissue samples from freshly resected colon segments were challenged ex vivo with the bile acid deoxycholate, approximately 50% of goblet cells became apoptotic by morphologic criteria. This high level of morphologic apoptosis allowed quantitative comparison with the usefulness and specificity of immunohistochemical markers of apoptosis. The antibody to c-CK18 was almost as useful and about as specific as morphology for identifying apoptotic colonic epithelial cells. Antibodies to c-cas-3, c-lam-A, and gammaH2AX, though specific for apoptotic cells, were less useful. The antibody to c-PARP, though specific for apoptotic cells, had low usefulness, and the antibody to AIF was relatively nonspecific, under our conditions.

Bile salt-induced apoptosis in human colon cancer cell lines involves the mitochondrial transmembrane potential but not the CD95 (Fas/Apo-1) receptor

BACKGROUND AND AIMS

Depending on their physico-chemical characteristics, bile acids can be potent inducers of apoptosis in colon cancer cells. This observation contrasts with bile acids being promoters of colorectal cancer carcinogenesis. Our recent observation of caspase activation in deoxycholate (DC)-treated colon cancer cell lines prompted us to analyze the mechanisms of bile acid-induced colon cancer cell death.

METHODS

CD95 expression was correlated to DC-induced cell death in four colon cancer cell lines. Mitochondrial transmembrane potential (MTP) was determined in whole cells as well as in isolated mitochondria.

RESULTS

On 2 of the 4 human colon cancer cell lines investigated, no CD95 was detected. These data were supported by a lack of CD95 mRNA in those cell lines that did not express CD95 on their surface. The apoptotic response to bile acids did not correlate with CD95 receptor expression on the respective cell lines. Therefore, we analyzed the MTP after the addition of toxic bile acids. MTP was destabilized early after the addition of deoxycholate to SW480 cells. These data were confirmed in isolated mitochondria, which showed strong swelling after the addition of DC. Accordingly, release of cytochrome-c from the mitochondrial intermembrane space into the cytosol, indicating dissipation of the MTP, and subsequent caspase-3 cleavage were detectable as early as 3 min after the addition of DC.

CONCLUSION

In contrast to hepatocytes and hepatic carcinoma cell lines, DC induces apoptosis in colon cancer cell lines via a CD95 receptor-independent mechanism. Direct induction of the mitochondrial permeability transition by toxic bile acids is suggested as the apoptosis-inducing mechanism in colon cancer cells.

Apoptosis resistance in Barrett's esophagus: ex vivo bioassay of live stressed tissues

BACKGROUND AND AIMS

Barrett's esophagus (BE) is a premalignant lesion of the distal esophagus in which squamous epithelial cells are replaced by metaplastic intestinal-like columnar epithelium that contains goblet cells. The factors that contribute to the progression from normal squamous mucosa to BE, Barrett's dysplasia, and adenocarcinoma are not well understood at the molecular level. Since reflux of bile acids is associated with BE development, we speculate that cells with an apoptosis-resistant phenotype are selected after long-term repeated exposure to pulses of bile acids. This will result in the survival of cells with unrepaired DNA damage, and a consequent increase in genomic instability leading to cancer progression. The major goal of this study is to compare sensitivity to apoptosis induced by the bile acid, deoxycholate (DOC), a known inducer of apoptosis, in normal esophageal squamous epithelium, normal colon epithelium, and BE.

METHODS

Thirteen patients with a confirmed diagnosis of BE and four patients who had undergone clinically indicated colectomy were included in the present study. Freshly obtained biopsies were incubated with control medium or medium supplemented with 1 mM DOC for 3 h and then evaluated for apoptotic changes using transmission electron microscopy and immunohistochemical staining for two apoptotic markers, cleaved caspase 3 and cleaved cytokeratin 18.

RESULTS

Our results indicate that BE is resistant to apoptosis induced by DOC compared to esophageal squamous epithelium and normal colon epithelium. In addition, electron micrographs revealed mitochondrial swelling in squamous epithelial cells treated ex vivo with DOC, which was absent in epithelial cells of BE. Formation of swollen mitochondria is an early marker of apoptotic cell death. Altogether, the data indicate that reduced apoptosis capability in BE tissue may contribute to progression to esophageal adenocarcinoma.

Role of aberrant crypt foci detected using high-magnification-chromoscopic colonoscopy in human colorectal carcinogenesis

Abstract Liaison between gastrointestinal endoscopists and histopathologists is essential to provide the highest standards of diagnostic accuracy and patient management. The histopathologist needs to be aware of the endoscopic findings when interpreting endoscopic biopsies. High-magnification-chromoscopic-colonoscopy (HMCC) is a new technology that provides the endoscopists with much greater resolution and functional staining of the gastrointestinal tract. Using HMCC, the endoscopist is now able to identify subtle changes in the colorectal luminal openings or crypts. Changes in crypt appearances now allow detection of aberrant crypt foci (ACF) in the colon, which might themselves be precancerous lesions but additionally might serve as a valid biomarker of subsequent adenoma and colorectal cancer formation. This article describes the role of the aberrant crypt focus in colorectal carcinogenesis and discusses the clinical impact of HMCC techniques as applicable to ACF.

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.

Increased Expression and Secretion of Interleukin-6 in Patients with Barrett’s Esophagus

Purpose: Barrett’s esophagus (BE) is a common premalignant lesion of the distal part of the esophagus that arises as a consequence of chronic duodenogastroesophageal reflux. Interleukin (IL)-6 is a pleiotropic cytokine that regulates immune defense mechanisms and hematopoiesis. In addition, IL-6 may also be involved in malignant transformation and tumor progression. IL-6 has been shown to inhibit apoptosis. The major aim of this study was to evaluate expression of IL-6 in BE at the protein and mRNA levels. In addition, we tested whether proteins that are associated with IL-6 signaling, phosphorylated signal transducer and activator of transcription 3 and two antiapoptotic proteins, Bcl-xL and Mcl-1, are also expressed in the same tissues.

Experimental Design: Biopsies of duodenum, BE, and squamous epithelium were evaluated by using a human cytokine protein array, ELISA, real-time PCR, and immunohistochemistry.

Results: Increased IL-6 levels were found to be secreted from BE tissue compared with duodenum or squamous epithelium from sites adjacent or 5 cm away from the BE lesion. IL-6 mRNA was also elevated in BE compared with duodenum or squamous epithelium in five of seven patients. Immunohistochemical studies confirmed IL-6 expression in intestinal glandular epithelium in BE tissue. Activated signal transducer and activator of transcription 3, Mcl-1, and Bcl-xL are present at higher levels in BE glands, with lower levels being found in duodenum or squamous epithelium

Conclusions: These data, taken together, suggest that elevated IL-6 levels in BE may contribute to the development of apoptosis resistance, thereby placing this epithelium at higher risk of developing malignancy.

Deoxycholate, an endogenous tumor promoter and DNA damaging agent, modulates BRCA-1 expression in apoptosis-sensitive epithelial cells: loss of BRCA-1 expression in colonic adenocarcinomas

Deoxycholate, a bile salt present at high levels in the colonic lumen of individuals on a high-fat diet, is a promoter of colon cancer. Deoxycholate also causes DNA damage. BRCA-1 functions in repair of DNA and in induction of apoptosis. We show that, when cultured cells of colonic origin are exposed to deoxycholate at different concentrations, BRCA-1 expression is induced at a low noncytotoxic concentration (10 microM) but is strongly inhibited at higher cytotoxic concentrations ( > or =100 microM). Indication of phosphorylation of BRCA-1 by deoxycholate (100 microM) at a lower dose was seen by Western blot analysis, whereas, at a higher dose, deoxycholate (200 and 300 microM) caused a complete loss of BRCA-1 expression. We show that BRCA-1 is substantially lower in colon adenocarcinomas from five patients compared with associated non-neoplastic colon tissue from the same patients, suggesting that the loss of BRCA-1 expression contributes to the malignant phenotype. In the non-neoplastic colon tissue, BRCA-1 was localized to the nongoblet cells. Our results imply that reduced expression of BRCA-1 may be associated with carcinoma of the colon.

DNA integrity as a potential marker for stool-based detection of colorectal cancer

BACKGROUND

Molecular genetic analysis of DNA in patient stools has been proposed for screening of colorectal cancer (CRC). Because nonapoptotic cells shed from tumors may contain DNA that is less degraded than DNA fragments from healthy colonic mucosa, our aim was to show that DNA fragments isolated from stools of patients with CRC had higher integrity than DNA isolated from stools of patients with healthy colonic mucosa.

METHODS

We purified DNA from the stools of a colonoscopy-negative control group and patients with CRC and examined the relationship between long DNA fragments and clinical status by determining stool DNA integrity, using oligonucleotide-based hybrid captures with specific target sequences in increasingly long PCR reactions (200 bp, 400 bp, 800 bp, 1.3 kb, 1.8 kb, 24 kb). DNA fragments obtained from CRC patients were compared with fragments obtained from colonoscopy-negative individuals for length and/or integrity.

RESULTS

DNA fragments isolated from CRC patients were of higher molecular weight (>18 bands detected of a total of 24 possible bands) than fragments isolated from fecal DNA of the colonoscopy-negative control group.

CONCLUSIONS

The presence of long DNA fragments in stool is associated with CRC and may be related to disease-associated differences in the regulation of proliferation and apoptosis. An assay of fecal DNA integrity may be a useful biomarker for the detection of CRC.

Nicotine increases oxidative stress, activates NF-kappaB and GRP78, induces apoptosis and sensitizes cells to genotoxic/xenobiotic stresses by a multiple stress inducer, deoxycholate: relevance to colon carcinogenesis

Epidemiologic studies indicate that environmental (smoking) and dietary factors (high fat) contribute to carcinogenesis in many organ systems. The aim of our study was to test the hypothesis that nicotine, a component of cigarette smoke, and sodium deoxycholate (NaDOC), a cytotoxic bile salt that increases in concentration in the gastrointestinal tract after a high fat meal, induce similar cellular stresses and that nicotine may enhance some of the NaDOC-induced stresses. We found that nicotine, at 0.8 microM, the very low sub-micromolar level occurring in the tissues of smokers: (1). increases oxidative stress; (2). activates NF-kappaB, a redox-sensitive transcription factor; (3). activates the 78 kD glucose regulated protein promoter, an indication of endoplasmic reticulum stress; (4). induces apoptosis; (5). enhances the ability of NaDOC to activate the 153 kD growth arrest and DNA damage promoter, an indication of increased genotoxic stress; and (6). enhances the ability of NaDOC to activate the xenobiotic response element. Our findings have applicability to G.I. cancer, in general, since smoking is a risk factor in the development of esophageal, pancreatic, gastric and colon cancer, and these cancers are also promoted by bile acids.

Effects of bile acids on base hydroxylation in a model of human colonic mucosal DNA

BACKGROUND AND AIMS

Increased intestinal bile acids as a possible consequence of a high fat/meat, low fiber diet are believed to play an important role in the formation of colon cancer. Interactions of bile salts particularly secondary bile acids with different cell components including DNA may contribute to carcinogenesis. To further investigate DNA damage by bile salts, we assessed the effects of a bile salt mixture containing deoxycholate and chenodeoxycholate on base hydroxylation in Chelex-treated DNA from calf thymus as a model of human colonic mucosal DNA in the presence and absence of reactive oxygen metabolites (ROM).

METHODS

Chelex-treated DNA from calf thymus (to remove residual iron impurities) was incubated with different bile salt concentrations (4 microM, 4.0 mM) (20.0% deoxycholate, 21.0% chenodeoxycholate) in the presence and absence of an OH generating system (25 microM FeCl3, 50 microM H2O2, 100 microM nitrilotriacetic acid) for 18 h (37 degrees C). After hydrolyzation, lyophilization and derivatization hydroxylated DNA bases were characterised and quantitated with gas chromatography-mass spectrometry (GS-MS) and SIM analysis. Two concentration ranges of bile salts were used, micromolar concentrations being present in plasma, millimolar in the gut lumen.

RESULTS

In the absence of ROM Chelex-treated DNA preparations contain only small amounts of hydroxylated base products. Bile salts at 4.0 mM significantly increased the amounts of 5-OH uracil and cis-thymine glycol. In the presence of ROM bile salts at 4.0 microM increased the production of 8-OH adenine and 8-OH guanine whereas bile salts at 4.0 mM inhibited ROM-induced base hydroxylation.

DISCUSSION

In the absence of ROM millimolar concentrations of a bile salt mixture with deoxycholate and chenodeoxycholate increase basal (spontaneous) DNA hydroxylation, whereas, they are without effects at micromolar concentrations. In the presence of ROM micromolar concentrations enhance oxidative DNA damage and millimolar concentrations were inhibitory. These results support the view that bile acids may cause oxidative DNA damage depending on their concentrations and the surrounding conditions both directly (enhancement of basal hydroxylation) and indirectly (enhancement of ROM-induced hydroxylation).

Long-term effects of ovarian follicular depletion in rats by 4-vinylcyclohexene diepoxide

4-Vinylcyclohexene diepoxide (VCD) destroys preantral ovarian follicles in rats. Female 28-day Fisher 344 (F344) rats were dosed (30 days) with VCD (80 mg/kg per day, i.p.) or vehicle, and animals were evaluated for reproductive function at subsequent time points for up to 360 days. At each time point animals were killed, and ovaries and plasma collected. VCD reduced (P<0.05) the number of preantral follicles by day 30 relative to control. There were no ultrastructural differences in morphology between VCD-treated and control ovaries. Circulating FSH levels in VCD-treated animals were greater (days 120, 240, and 360, P<0.05) than in controls. Cyclicity was disrupted in the VCD-treated group by day 360. These results show that VCD-induced follicular destruction in rats is associated with a sequence of events (loss of preantral follicles, increased plasma FSH, and cyclic disruption) preceding premature ovarian senescence that is similar to events that occur during the onset of menopause in women.

Diet and cancer: assessing the risk

Globally, colorectal cancer (CRC) is a leading cause of mortality from malignant disease. Case-control and cohort studies provide strong support for a role of diet in the aetiology of CRC. However to establish causal relationships and to identify more precisely the dietary components involved, intervention studies in human subjects are required. Cancer is an impractical endpoint in terms of numbers, cost, study duration and ethical considerations. Consequently, intermediate biomarkers of the disease are required. This review aims to provide an overview of the intermediate endpoints available for the study of CRC, particularly non-invasive faecal biomarkers. Examples of their use in dietary intervention studies are given.

Patchy field defects of apoptosis resistance and dedifferentiation in flat mucosa of colon resections from colon cancer patients

BACKGROUND

Abnormal areas in normal-appearing flat colonic mucosa (field defects) may predispose individuals to colon cancer. Markers of field defects would indicate cancer risk.

METHODS

We evaluated apoptosis capability, dedifferentiation, frequency of simple aberrant crypts, aberrant crypt foci, microadenomas, and total nicotinamide adenine dinucleotide levels at locations within normal-appearing flat mucosa obtained from colon resections.

RESULTS

Among goblet cells from colonic mucosa samples of individuals without colonic neoplasia, there was a high mean deoxycholate-induced apoptotic index (AI) of 59.1% and high Dolichos biflorus agglutinin (DBA) lectin reactivity (differentiation) in 85.0% of samples. In contrast, flat mucosa samples from colon cancer patients had a significantly (P <.01) lower average AI of 37.4%, and a significantly (P =.03) lower percentage (40.5%) had high DBA reactivity. For colon cancer patients, AI and DBA reactivity values were patchy within a resection. Nicotinamide adenine dinucleotide levels were highly variable among individuals without neoplasia, and aberrant crypt foci and microadenomas were rare.

CONCLUSIONS

AI and aberrant DBA reactivity are promising indicators of colon cancer risk. Our results attest to the importance of obtaining multiple samples to assess colon cancer risk because of the patchy nature of field defects.

Role of mitochondrial complexes I and II, reactive oxygen species and arachidonic acid metabolism in deoxycholate-induced apoptosis

Bile acids are promoters of colon cancer; however, the mechanism(s) of action of this tumor promoter are largely unknown. Bile acids induce apoptosis in colon epithelial cells and it is probable that the modulation of apoptosis contributes, in part, to colon carcinogenesis. We tested the hypothesis that damage to mitochondria is an upstream event in sodium deoxycholate (NaDOC)-induced apoptosis and that a pro-oxidant state of the cell favors survival. NaDOC-induced damage to mitochondria was assessed by a decrease in mitochondrial membrane potential using flow cytometry and an increase in megamitochondria formation using transmission electron microscopy. We found that inhibition of mitochondrial complexes I and II with rotenone and thenoyltrifluoroacetone, respectively, dramatically protected HT-29 cells against NaDOC-induced apoptosis. Antioxidants (e.g. lazaroids U-74389G and U-8389G), however, sensitized cells to NaDOC-induced apoptosis, in spite of a reduction in reactive oxygen/nitrogen species. Lazaroid pre-treatment caused a marked decrease in NaDOC-induced activation of the anti-apoptotic transcription factor, NF-kappaB, which may provide the basis for the sensitization to apoptosis caused by these antioxidants. Inhibitors of arachidonic acid metabolism (e.g. esculetin, sulindac sulfide, NS-398) also sensitized HT-29 cells to NaDOC-induced apoptosis. These results indicate that the life/death decision is the result of a shift in the balance between specific anti-apoptotic and pro-apoptotic factors, respectively, that may have significance to colon carcinogenesis.

Short-chain fatty acids and human colonic function: roles of resistant starch and nonstarch polysaccharides

Resistant starch (RS) is starch and products of its small intestinal digestion that enter the large bowel. It occurs for various reasons including chemical structure, cooking of food, chemical modification, and food mastication. Human colonic bacteria ferment RS and nonstarch polysaccharides (NSP; major components of dietary fiber) to short-chain fatty acids (SCFA), mainly acetate, propionate, and butyrate. SCFA stimulate colonic blood flow and fluid and electrolyte uptake. Butyrate is a preferred substrate for colonocytes and appears to promote a normal phenotype in these cells. Fermentation of some RS types favors butyrate production. Measurement of colonic fermentation in humans is difficult, and indirect measures (e.g., fecal samples) or animal models have been used. Of the latter, rodents appear to be of limited value, and pigs or dogs are preferable. RS is less effective than NSP in stool bulking, but epidemiological data suggest that it is more protective against colorectal cancer, possibly via butyrate. RS is a prebiotic, but knowledge of its other interactions with the microflora is limited. The contribution of RS to fermentation and colonic physiology seems to be greater than that of NSP. However, the lack of a generally accepted analytical procedure that accommodates the major influences on RS means this is yet to be established.

Ultrastructural evaluation of oocytes during atresia in rat ovarian follicles

Mammalian females are born with a finite number of ovarian oocytes, the vast majority of which ultimately undergo degeneration by atresia. The overall process of ovarian follicular atresia has been morphologically well described only in large antral follicles. Additionally, little attention has been focused on ultrastructural changes in the oocyte. Furthermore, most such morphological studies were performed prior to identification of apoptosis as a mechanism of physiological cell death. Therefore, the purpose of this study was to use electron microscopy to compare the process of atretic oocyte degradation in ovarian follicles of female Fischer 344 rats (38 days old) with ultrastructural characteristics of apoptosis. Examination of ovarian follicles revealed that nucleolar segregation, cytoplasmic or nuclear condensation, apoptotic body formation, and chromatin margination along the nuclear membrane are never observed in atretic oocytes during the degenerative process. Instead, early morphological changes in atretic oocytes include retraction of granulosa cell- and oocyte-derived microvilli and condensation of mitochondria and loss of cristae. These occurrences coincide with initiation of granulosa cell apoptosis. After most granulosa cells are lost, more severe changes occur, including segmentation of the oocyte and cytoplasmic vacuolization as atresia progresses. Thus, these results suggest that, during atresia, oocytes are removed by physiological oocyte cell death, a method that does not involve classically described apoptosis.

Effect of colonic luminal components on induction of apoptosis in human colonic cell lines

Apoptosis is central to cell number regulation in the colonic epithelium, and interest in its role in colon carcinogenesis has been growing rapidly. It thus becomes of interest to characterize luminal components, possibly of dietary origin, that may influence this process. We have investigated the sensitivity of two human colonic cell lines, the human adenocarcinoma cell line (HT-29) and the human fetal colonic mucosa cell line (FHC), to induction of apoptosis by sodium butyrate, bile acids, and human fecal water fractions. The apoptotic effect has been studied by 1) morphological changes in cells examined by fluorescence microscopy, 2) DNA fragmentation analysis by gel electrophoresis, 3) flow cytometry analysis of DNA strand breaks assessed by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay (TUNEL), and 4) poly(ADP-ribose) polymerase cleavage by Western blot. Sodium butyrate and bile acids induced a time- and concentration-dependent apoptosis in both cell lines. Quantitation of this effect, by use of the TUNEL assay, indicated that deoxycholic acid was most effective in inducing this effect at lower concentrations and at shorter times. Apoptotic effects were also observed, in both cell lines, when the cells were exposed to intact human fecal waters (the fecal fraction in direct contact with the epithelium) and their lipid extracts, with the intact samples being more effective. Although all fecal waters examined induced apoptosis, quantitation of the effect by the TUNEL assay indicated that the ability to induce apoptosis differed markedly between samples. Induction of apoptosis by the fecal waters was not correlated to cytotoxicity but was negatively correlated to the pH of the samples. Interestingly, the cells derived from the fetal mucosa (FHC) were consistently less sensitive to apoptotic effects of the luminal components than the tumor-derived cells (HT-29). Thus human fecal water fractions induce apoptosis in colonic cells, and this effect is not due to lipid components alone.

Evaluation of fecal mutagenicity and colorectal cancer risk

Colorectal cancer is one of the most common internal malignancies in Western society. The cause of this disease appears to be multifactorial and involves genetic as well as environmental aspects. The human colon is continuously exposed to a complex mixture of compounds, which is either of direct dietary origin or the result of digestive, microbial and excretory processes. In order to establish the mutagenic burden of the colorectal mucosa, analysis of specific compounds in feces is usually preferred. Alternatively, the mutagenic potency of fecal extracts has been determined, but the interpretation of these more integrative measurements is hampered by methodological shortcomings. In this review, we focus on exposure of the large bowel to five different classes of fecal mutagens that have previously been related to colorectal cancer risk. These include heterocyclic aromatic amines (HCA) and polycyclic aromatic hydrocarbons (PAH), two exogenous factors that are predominantly ingested as pyrolysis products present in food and (partially) excreted in the feces. Additionally, we discuss N-nitroso-compounds, fecapentaenes and bile acids, all fecal constituents (mainly) of endogenous origin. The mutagenic and carcinogenic potency of the above mentioned compounds as well as their presence in feces, proposed mode of action and potential role in the initiation and promotion of human colorectal cancer are discussed. The combined results from in vitro and in vivo research unequivocally demonstrate that these classes of compounds comprise potent mutagens that induce many different forms of genetic damage and that particularly bile acids and fecapentaenes may also affect the carcinogenic process by epigenetic mechanisms. Large inter-individual differences in levels of exposures have been reported, including those in a range where considerable genetic damage can be expected based on evidence from animal studies. Particularly, however, exposure profiles of PAH and N-nitroso compounds (NOC) have to be more accurately established to come to a risk evaluation. Moreover, lack of human studies and inconsistency between epidemiological data make it impossible to describe colorectal cancer risk as a result of specific exposures in quantitative terms, or even to indicate the relative importance of the mutagens discussed. Particularly, the polymorphisms of genes involved in the metabolism of heterocyclic amines are important determinants of carcinogenic risk. However, the present knowledge of gene-environment interactions with regard to colorectal cancer risk is rather limited. We expect that the introduction of DNA chip technology in colorectal cancer epidemiology will offer new opportunities to identify combinations of exposures and genetic polymorphisms that relate to increased cancer risk. This knowledge will enable us to improve epidemiological study design and statistical power in future research.

Vascular apoptosis and involution in gliomas precede neovascularization: a novel concept for glioma growth and angiogenesis

Vascular changes in gliomas were analyzed by implanting fluorescent-labeled glioma 261 cells in the brains of 28 mice. Seven animals were killed each week for 4 weeks. We investigated the expression of angiopoietin-2 (Ang-2) by in situ hybridization and compared it with the distribution of apoptotic cells identified by DNA strand breaks (using the terminal deoxynucleotidyl transferase-mediated biotinylated deoxyuridine triphosphate nick end labeling [TUNEL] method) and transmission electron microscopy (TEM). As early as 1 week after implantation, tumor cells accumulated around vessels, which expressed Ang-2 and were TUNEL negative. TEM showed tumor cells adjacent to the vascular cells "lifting up" the normal astrocytic feet processes away from the endothelial cells and disrupting normal pericytic cuffing. After 2 weeks the number of perivascular glioma cells had increased. No increase in the number of blood vessels was detected at this time. Vascular cells remained positive for Ang-2 and rare ones were TUNEL positive. TEM showed closely packed proliferating perivascular tumor cells. After 3 weeks, there was vascular involution with scant zones of tumor necrosis. Ang-2 was still detected in vascular cells, but now numerous vascular cells were TUNEL positive. In addition, TEM showed apoptotic vascular cells. After 4 weeks, there were extensive areas of tumor necrosis with pseudopalisading and adjacent angiogenesis. Ang-2 was detected in vascular cells at the edge of the tumors in the invaded brain and in vessels surrounded by tumor cells. At both 3 and 4 weeks, most of the TUNEL-positive tumor cells lacked morphological features characteristic of apoptosis and displayed features consistent with necrotic cell death as determined by TEM. Only rare tumor cells appeared truly apoptotic. In contrast, the TUNEL-positive endothelial cells and pericytes were round and shrunken, with condensed nuclear chromatin by TEM, suggesting that vascular cells were undergoing an apoptotic cell death. These results suggest that vascular cell apoptosis and involution preceded tumor necrosis and that angiogenesis is a later event in tumor progression in experimental gliomas. Moreover, Ang-2 is detected prior to the onset of apoptosis in vascular cells and could be linked to vascular involution.

Role of nitric oxide and peroxynitrite in bile salt-induced apoptosis: relevance to colon carcinogenesis

Previous work from our laboratory indicated that the bile salt sodium deoxycholate (NaDOC) induced apoptosis in cultured cells and in normal goblet cells of the colonic mucosa. We also reported that the normal-appearing flat mucosa of patients with colon cancer exhibited apoptosis resistance. Using immunofluorescence in conjunction with confocal microscopy, we now report that high physiological concentrations (0.5 mM) of NaDOC result in the formation of nitrotyrosine residues, a footprint for the formation of reactive nitrogen species, including peroxynitrite, in plasma membrane-associated proteins of HT-29 cells. Because peroxynitrite is formed from the reaction between nitric oxide and superoxide anion, we specifically looked at the role of nitric oxide and superoxide anion in NaDOC-induced apoptosis. Pretreatment of cells with the inhibitor/antioxidants, N-nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthase, copper (II) 3,5-diisopropyl salicylate hydrate, a superoxide dismutase mimetic compound, and Trolox, a water-soluble analog of alpha-tocopherol, alone or in combination, sensitized cells to apoptosis induced by 0.5 mM NaDOC. These results suggest that nitric oxide may be part of a signaling pathway that is responsible for apoptosis resistance. The results also indicate that nitric oxide does not appear to protect cells against NaDOC-induced apoptosis by scavenging superoxide anion.

The NAD+ precursors, nicotinic acid and nicotinamide protect cells against apoptosis induced by a multiple stress inducer, deoxycholate

The bile salt, sodium deoxycholate (NaDOC), is a natural detergent that promotes digestion of fats. At high physiologic levels, NaDOC activates many stress-response pathways and induces apoptosis in various cell types. NaDOC induces DNA damage and activates poly(ADP-ribose) polymerase (PARP), an enzyme that utilizes NAD+ as a substrate to repair DNA. NaDOC also induces oxidative stress, endoplasmic reticulum (ER) stress and contributes to protein malfolding. The NAD+ precursors, nicotinic acid (NA) and nicotinamide (NAM) were found to protect cells against NaDOC-induced apoptosis. NA and NAM also decreased constitutive levels of both activated NF-kappaB and GRP78, two proteins that respond to oxidative stress. However, the mechanism by which NA and NAM protects cells against apoptosis does not involve a reduction in constitutive levels of oxidative stress. NA or NAM treatment increased the protein levels of glyceraldehyde-3-phosphate dehydrogense (GAPDH), a multi-functional enzyme, in the nucleus and cytoplasm, respectively. NAM did not activate the promoter/response elements of 13 stress response genes nor reduce intracellular non-protein thiols, suggesting that it is non-toxic to cells. NAM thus has promise as a dietary supplement to help prevent disorders involving excessive apoptosis.

Aberrant crypt foci in colorectal carcinogenesis. Cell and crypt dynamics

Aberrant crypt foci (ACF) have been identified on the colonic mucosal surface of rodents treated with colon carcinogens and of humans after methylene-blue staining and observation under a light microscope. Several lines of evidence strongly suggest that ACF with certain morphological, histological, cell kinetics, and genetic features are precursor lesions of colon cancer both in rodents and in humans. Thus, ACF represent the earliest step in colorectal carcinogenesis. This paper has the main purpose of reviewing the evidence supporting this view, with particular emphasis on cell and crypt dynamics in ACF. ACF have been used as intermediate biomarkers of cancer development in animal studies aimed at the identification of colon carcinogens and chemopreventive agents. Recently, evidence has also shown that ACF can be effectively employed in chemopreventive studies also in humans.