Ca2+- and PKC-dependent stimulation of PGE2 synthesis by deoxycholic acid in human colonic fibroblasts

A review on the effect of COX-2-mediated mechanisms on development and progression of gastric cancer induced by nicotine

Smoking is a documented risk factor for cancer, e.g., gastric cancer. Nicotine, the principal tobacco alkaloid, would exert its role of contribution to gastric cancer development and progression through nicotinic acetylcholine receptors (nAChRs) and β-adrenergic receptors (β-ARs), which then promote cancer cell proliferation, migration and invasion. As a key isoenzyme in conversion of arachidonic acid to prostaglandins, cyclooxygenase-2 (COX-2) has been demonstrated to have a wide range of effects in carcinogenesis and tumor development. At present, many studies have reported the effect of nicotine on gastric cancer by binding to nAChR, as well as indirectly stimulating β-AR to mediate COX-2-related pathways. This review summarizes these studies, and also proposes more potential COX-2-mediated mechanisms. These events might contribute to the growth and progression of gastric cancer exposed to nicotine through tobacco smoke or cigarette substitutes. Also, this review article has therefore the potential not only to make a significant contribution to the treatment and prognosis of gastric cancer for smokers but also to the clinical application of COX-2 antagonists. In addition, this work also discusses the considerable challenges of this field with special reference to the future perspective of COX-2-mediated mechanisms in development and progression of gastric cancer induced by nicotine.

Versatile Triad Alliance: Bile Acid, Taurine and Microbiota

Taurine is the most abundant free amino acid in the body, and is mainly derived from the diet, but can also be produced endogenously from cysteine. It plays multiple essential roles in the body, including development, energy production, osmoregulation, prevention of oxidative stress, and inflammation. Taurine is also crucial as a molecule used to conjugate bile acids (BAs). In the gastrointestinal tract, BAs deconjugation by enteric bacteria results in high levels of unconjugated BAs and free taurine. Depending on conjugation status and other bacterial modifications, BAs constitute a pool of related but highly diverse molecules, each with different properties concerning solubility and toxicity, capacity to activate or inhibit receptors of BAs, and direct and indirect impact on microbiota and the host, whereas free taurine has a largely protective impact on the host, serves as a source of energy for microbiota, regulates bacterial colonization and defends from pathogens. Several remarkable examples of the interaction between taurine and gut microbiota have recently been described. This review will introduce the necessary background information and lay out the latest discoveries in the interaction of the co-reliant triad of BAs, taurine, and microbiota.

The Role of Cyclooxygenase-2 in Colorectal Cancer

Colorectal cancer is the third common cancer in this world, accounting for more than 1 million cases each year. However, detailed etiology and mechanism of colorectal cancer have not been fully understood. For example, cyclooxygenase-2 (COX-2) and its product prostaglandin E₂ (PGE₂) have been closely linked to its occurrence, progression and prognosis. However, the mechanisms on how COX-2 and PGE₂-mediate the pathogenesis of colorectal cancer are obscure. In this review, we have summarized recent advances in studies of pathogenesis and control in colorectal cancer to assist further advances in the research for the cure of the cancer. In addition, the knowledge gained may also guide the audiences for reduction of the risk and control of this deadly disease.

Eicosanoids and HB-EGF/EGFR in cancer

Eicosanoids are bioactive lipids that play crucial roles in various pathophysiological conditions, including inflammation and cancer. They include both the COX-derived prostaglandins and the LOX-derived leukotrienes. Furthermore, the epidermal growth factor receptor (EGFR) pathways family of receptor tyrosine kinases also are known to play a central role in the tumorigenesis. Various antitumor modalities have been approved cancer treatments that target therapeutically the COX-2 and EGFR pathways; these include selective COX-2 inhibitors and EGFR monoclonal antibodies. Research has shown that the COX-2 and epidermal growth factor receptor pathways actively interact with each other in order to orchestrate carcinogenesis. This has been used to justify a targeted combinatorial approach aimed at these two pathways. Although combined therapies have been found to have a greater antitumor effect than the administration of single agent, this does not exempt them from the possible fatal cardiac effects that are associated with COX-2 inhibition. In this review, we delineate the contribution of HB-EGF, an important EGFR ligand, to the cardiac dysfunction related to decreased shedding of HB-EGF after COX-2/PGE2 inhibition. A better understanding of the molecular mechanisms underlying these cardiac side effects will make possible more effective regimens that use the dual-targeting approach.

Role of bile acids in colon carcinogenesis

Bile acids (BAs) are cholesterol derivatives synthesized in the liver and then secreted into the intestine for lipid absorption. There are numerous scientific reports describing BAs, especially secondary BAs, as strong carcinogens or promoters of colon cancers. Firstly, BAs act as strong stimulators of colorectal cancer (CRC) initiation by damaging colonic epithelial cells, and inducing reactive oxygen species production, genomic destabilization, apoptosis resistance, and cancer stem cells-like formation. Consequently, BAs promote CRC progression via multiple mechanisms, including inhibiting apoptosis, enhancing cancer cell proliferation, invasion, and angiogenesis. There are diverse signals involved in the carcinogenesis mechanism of BAs, with a major role of epidermal growth factor receptor, and its down-stream signaling, involving mitogen-activated protein kinase, phosphoinositide 3-kinase/Akt, and nuclear factor kappa-light-chain-enhancer of activated B cells. BAs regulate numerous genes including the human leukocyte antigen class I gene, p53, matrix metalloprotease, urokinase plasminogen activator receptor, Cyclin D1, cyclooxygenase-2, interleukin-8, and miRNAs of CRC cells, leading to CRC promotion. These evidence suggests that targeting BAs is an efficacious strategies for CRC prevention and treatment.

The regulation of host cellular and gut microbial metabolism in the development and prevention of colorectal cancer

Metabolism regulation is crucial in colorectal cancer (CRC) and has emerged as a remarkable field currently. The cellular metabolism of glucose, amino acids and lipids in CRC are all reprogrammed. Each of them changes tumour microenvironment, modulates bacterial composition and activity, and eventually promotes CRC development. Metabolites such as short chain fatty acids, secondary bile acids, N-nitroso compounds, hydrogen sulphide, polyphenols and toxins like fragilysin, FadA, cytolethal distending toxin and colibactin play a dual role in CRC. The relationship of gut microbe-metabolite is essential in remodelling intestinal microbial ecology composition and metabolic activity. It regulates the metabolism of colonic epithelial cells and changes the tumour microenvironment in CRC. Microbial metabolism manipulation has been considered to be potentially preventive in CRC, but more large-scale clinical trials are required before their application in clinical practice in the near future.

Inhibition of STAT3- and MAPK-dependent PGE2 synthesis ameliorates phagocytosis of fibrillar β-amyloid peptide (1-42) via EP2 receptor in EMF-stimulated N9 microglial cells

Background

Prostaglandin E₂ (PGE₂)-involved neuroinflammatory processes are prevalent in several neurological conditions and diseases. Amyloid burden is correlated with the activation of E-prostanoid (EP) 2 receptors by PGE₂ in Alzheimer’s disease. We previously demonstrated that electromagnetic field (EMF) exposure can induce pro-inflammatory responses and the depression of phagocytosis in microglial cells, but the signaling pathways involved in phagocytosis of fibrillar β-amyloid (fAβ) in microglial cells exposed to EMF are poorly understood. Given the important role of PGE₂ in neural physiopathological processes, we investigated the PGE₂-related signaling mechanism in the immunomodulatory phagocytosis of EMF-stimulated N9 microglial cells (N9 cells).

Methods

N9 cells were exposed to EMF with or without pretreatment with the selective inhibitors of cyclooxygenase-2 (COX-2), Janus kinase 2 (JAK2), signal transducer and activator of transcription 3 (STAT3), and mitogen-activated protein kinases (MAPKs) and antagonists of PG receptors EP1-4. The production of endogenous PGE₂ was quantified by enzyme immunoassays. The phagocytic ability of N9 cells was evaluated based on the fluorescence intensity of the engulfed fluorescent-labeled fibrillar β-amyloid peptide (1-42) (fAβ₄₂) measured using a flow cytometer and a fluorescence microscope. The effects of pharmacological agents on EMF-activated microglia were investigated based on the expressions of JAK2, STAT3, p38/ERK/JNK MAPKs, COX-2, microsomal prostaglandin E synthase-1 (mPGES-1), and EP2 using real-time PCR and/or western blotting.

Results

EMF exposure significantly increased the production of PGE₂ and decreased the phagocytosis of fluorescent-labeled fAβ₄₂ by N9 cells. The selective inhibitors of COX-2, JAK2, STAT3, and MAPKs clearly depressed PGE₂ release and ameliorated microglial phagocytosis after EMF exposure. Pharmacological agents suppressed the phosphorylation of JAK2-STAT3 and MAPKs, leading to the amelioration of the phagocytic ability of EMF-stimulated N9 cells. Antagonist studies of EP1-4 receptors showed that EMF depressed the phagocytosis of fAβ₄₂ through the PGE₂ system, which is linked to EP2 receptors.

Conclusions

This study indicates that EMF exposure could induce phagocytic depression via JAK2-STAT3- and MAPK-dependent PGE₂-EP2 receptor signaling pathways in microglia. Therefore, pharmacological inhibition of PGE₂ synthesis and EP2 receptors may be a potential therapeutic strategy to combat the neurobiological deterioration that follows EMF exposure.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0762-9) contains supplementary material, which is available to authorized users.

The Role of Cyclooxygenase-2 in Colorectal Carcinogenesis

Colorectal cancer is a major worldwide health care problem that accounts for 1 million new cases each year. The risk factors for this disease include hereditary factors, environmental agents, and inflammatory stimuli that affect the gastrointestinal tract. Among these risk factors, cyclooxygenase-2 (COX-2) is one of the major players in the progression of colorectal cancer; however, the detailed mechanism of its role in causing colorectal cancer is still not well understood. In addition, the role of COX-2 signaling through the interaction in the epithelial and stromal compartments on colorectal carcinogenesis has not been fully illustrated. In the present review, we provide published evidence to demonstrate that (1) COX-2 signaling plays a major role in the progression of colorectal cancer, (2) activation of COX-2 in the stromal compartment also contributes to colorectal carcinogenesis, and (3) inhibition of COX-2 signaling by COX-2 inhibitors might be an effective method to control colorectal cancer. We have also summarized recent advances and insights from mechanistic studies of colorectal cancer to help prevent and control this deadly disease and provide our opinion regarding the importance of risk reduction and disease prevention for colorectal cancer.

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.

Regulation of myofibroblast differentiation by cardiac glycosides

Myofibroblast differentiation is a key process in pathogenesis of fibrotic diseases. Cardiac glycosides (ouabain, digoxin) inhibit Na(+)-K(+)-ATPase, resulting in increased intracellular [Na(+)]-to-[K(+)] ratio in cells. Microarray analysis suggested that increased intracellular [Na(+)]/[K(+)] ratio may promote the expression of cyclooxygenase-2 (COX-2), a critical enzyme in the synthesis of prostaglandins. Given antifibrotic effects of prostaglandins through activation of protein kinase A (PKA), we examined if cardiac glycosides stimulate COX-2 expression in human lung fibroblasts and how they affect myofibroblast differentiation. Ouabain stimulated a profound COX-2 expression and a sustained PKA activation, which was blocked by COX-2 inhibitor or by COX-2 knockdown. Ouabain-induced COX-2 expression and PKA activation were abolished by the inhibitor of the Na(+)/Ca(2+) exchanger, KB-R4943. Ouabain inhibited transforming growth factor-β (TGF-β)-induced Rho activation, stress fiber formation, serum response factor activation, and the expression of smooth muscle α-actin, collagen-1, and fibronectin. These effects were recapitulated by an increase in intracellular [Na(+)]/[K(+)] ratio through the treatment of cells with K(+)-free medium or with digoxin. Although inhibition of COX-2 or of the Na(+)/Ca(2+) exchanger blocked ouabain-induced PKA activation, this failed to reverse the inhibition of TGF-β-induced Rho activation or myofibroblast differentiation by ouabain. Together, these data demonstrate that ouabain, through the increase in intracellular [Na(+)]/[K(+)] ratio, drives the induction of COX-2 expression and PKA activation, which is accompanied by a decreased Rho activation and myofibroblast differentiation in response to TGF-β. However, COX-2 expression and PKA activation are not sufficient for inhibition of the fibrotic effects of TGF-β by ouabain, suggesting that additional mechanisms must exist.

Fusobacterium and Escherichia: models of colorectal cancer driven by microbiota and the utility of microbiota in colorectal cancer screening

Intestinal microbiota has emerging roles in the development of colorectal cancer (CRC). Intestinal dysbiosis, with altered levels of specific bacteria, is consistently seen in CRC. The heart of the debate lies in whether these bacteria are a cause or consequence of CRC. Two bacteria in particular, Fusobacterium nucleatum and Escherichia coli, have consistently been associated with CRC. This review will examine evidence supporting oncogenic roles of F. nucleatum and E. coli. The proposed mechanisms of tumor formation follow two models: bacterial induced chronic inflammation leads to cell proliferation and tumor formation and virulence factors directly induce tumor formation. This review will further examine the potential for microbiota as biomarkers in CRC, with a focus on F. nucleatum.

TNFα-activated stromal COX-2 signalling promotes proliferative and invasive potential of colon cancer epithelial cells

OBJECTIVES

Up to now it has been unclear whether stromal/epithelial interaction affects progression of colon cancer. This study was designed to examine effects of tumour necrosis factor alpha (TNFα)-activated stromal cyclooxygenase-2 (COX-2) signalling on proliferation and invasiveness of colon cancer epithelial cells.

MATERIALS AND METHODS

Cyclooxygenase-2 mRNA and protein were determined by real-time PCR and western blotting and prostaglandin E2 (PGE2 ) was assayed by radioimmunoassay. Cell proliferation and invasiveness were determined by transwell chamber assays and protein kinase C (PKC) was assayed by Biotrak(™) PKC Assay System.

RESULTS

Our results indicated that TNFα, a powerful inflammatory cytokine, strongly promoted COX-2 expression and PGE2 production in colon cancer-associated fibroblasts. Using in vitro assays for estimating proliferative and invasive potential, we discovered that activation of stromal COX-2 signalling significantly promoted proliferation and invasiveness of colon cancer epithelial cells. In addition, selective COX-2 inhibitor N-[2-(Cyclohexyloxy)-4-nitrophenyl]methanesulfonamide, blocked such proliferative and invasive effects on the cancer epithelial cells. In this process, PKC was involved in activation of COX-2 signalling in the fibroblasts.

CONCLUSION

We conclude that activation of stromal COX-2 signalling by TNFα played a major role in promoting proliferation and invasiveness of colon cancer epithelial cells.

Stromal COX-2 signaling activated by deoxycholic acid mediates proliferation and invasiveness of colorectal epithelial cancer cells

COX-2 is a major regulator implicated in colonic cancer. However, how COX-2 signaling affects colonic carcinogenesis at cellular level is not clear. In this article, we investigated whether activation of COX-2 signaling by deoxycholic acid (DCA) in primary human normal and cancer associated fibroblasts play a significant role in regulation of proliferation and invasiveness of colonic epithelial cancer cells. Our results demonstrated while COX-2 signaling can be activated by DCA in both normal and cancer associated fibroblasts, the level of activation of COX-2 signaling is significantly greater in cancer associated fibroblasts than that in normal fibroblasts. In addition, we discovered that the proliferative and invasive potential of colonic epithelial cancer cells were much greater when the cells were co-cultured with cancer associated fibroblasts pre-treated with DCA than with normal fibroblasts pre-treated with DCA. Moreover, COX-2 siRNA attenuated the proliferative and invasive effect of both normal and cancer associate fibroblasts pre-treated with DCA on the colonic cancer cells. Further studies indicated that the activation of COX-2 signaling by DCA is through protein kinase C signaling. We speculate that activation of COX-2 signaling especially in cancer associated fibroblasts promotes progression of colonic cancer.

Deoxycholic acid inhibits smooth muscle contraction via protein kinase C-dependent modulation of L-type Ca2+ channels in rat proximal colon

The aim of this study was to investigate the effects of deoxycholic acid (DCA) on the contractions of rat proximal colonic smooth muscle (PCSM) in vitro. The contractile response of rat PCSM strips was tested using a polyphysio-graph. The whole cell patch-clamp technique was also used in rat colonic smooth muscle cells (SMCs) isolated by an enzymatic procedure to record the L-type calcium current (I(Ca-L)) prior to and following the application of various concentrations of DCA. The application of DCA (10(-6)-10(-4) M) decreased the amplitude of spontaneous contractions of the PCSM strips in a dose-dependent manner. The administration of DCA (10(-5) M) caused the relaxation of isolated smooth muscle strips pre-contracted by acetylcholine (Ach) or KCl (by 12.2±1.5 and 16.3±6.9%, respectively). The concentration-response curve of CaCl2 was shifted to the right. Pre-treatment of the strips with the protein kinase C (PKC) inhibitor chelerythrine (1 µM) significantly attenuated the effects of DCA on the strips pre-contracted by Ach. DCA reduced the peak I(Ca-L) by 6.02±0.87% at 10(-6) M, 15.02±1.73% at 10(-5) M and 47.14±3.79% at 10(-4) M. DCA shifted the current-voltage (I-V) curve of ICa-L upward, but the contour of the I-V curve was unchanged, and the peak current-induced voltage remained at 0 mV. Pre-treatment with chelerythrine (1 µM) blocked the actions of DCA on the I(Ca-L). Taken together, the actions of DCA on I(Ca-L) in rat colonic SMCs contributed to a negative inotropic effect. These actions appear to be mediated through protein kinase C. Furthermore, this study suggests another possible mechanism for the DCA-related modulation of gastrointestinal motility.

Counteracting effect of TRPC1-associated Ca2+ influx on TNF-α-induced COX-2-dependent prostaglandin E2 production in human colonic myofibroblasts

TNF-α-NF-κB signaling plays a central role in inflammation, apoptosis, and neoplasia. One major consequence of this signaling in the gut is increased production of prostaglandin E(2) (PGE(2)) via cyclooxygenase-2 (COX-2) induction in myofibroblasts, which has been reported to be dependent on Ca(2+). In this study, we explored a potential role of canonical transient receptor potential (TRPC) proteins in this Ca(2+)-mediated signaling using a human colonic myofibroblast cell line CCD-18Co. In CCD-18Co cell, treatment with TNF-α greatly enhanced Ca(2+) influx induced by store depletion along with increased cell-surface expression of TRPC1 protein (but not of the other TRPC isoforms) and induction of a Gd(3+)-sensitive nonselective cationic conductance. Selective inhibition of TRPC1 expression by small interfering RNA (siRNA) or functionally effective TRPC1 antibody targeting the near-pore region of TRPC1 (T1E3) antagonized the enhancement of store-dependent Ca(2+) influx by TNF-α, whereas potentiated TNF-α induced PGE(2) production. Overexpression of TRPC1 in CCD-18Co produced opposite consequences. Inhibitors of NF-κB (curcumin, SN-50) attenuated TNF-α-induced enhancement of TRPC1 expression, store-dependent Ca(2+) influx, and COX-2-dependent PGE(2) production. In contrast, inhibition of calcineurin-nuclear factor of activated T-cell proteins (NFAT) signaling by FK506 or NFAT Activation Inhibitor III enhanced the PGE(2) production without affecting TRPC1 expression and the Ca(2+) influx. Finally, the suppression of store-dependent Ca(2+) influx by T1E3 antibody or siRNA knockdown significantly facilitated TNF-α-induced NF-κB nuclear translocation. In aggregate, these results strongly suggest that, in colonic myofibroblasts, NF-κB and NFAT serve as important positive and negative transcriptional regulators of TNF-α-induced COX-2-dependent PGE(2) production, respectively, at the downstream of TRPC1-associated Ca(2+) influx.

Ursodeoxycholic acid suppresses Cox-2 expression in colon cancer: roles of Ras, p38, and CCAAT/enhancer-binding protein

In the azoxymethane (AOM) model of experimental rodent colon cancer, cholic acid and its colonic metabolite deoxycholic acid (DCA) strongly promote tumorigenesis. In contrast, we showed that ursodeoxycholic acid (UDCA), a low abundance bile acid, inhibited AOM tumorigenesis. Dietary UDCA also blocked the development of tumors with activated Ras and suppressed cyclooxygenase-2 (Cox-2) upregulation in AOM tumors. In this study, we compared the effect of dietary supplementation with tumor-promoting cholic acid to chemopreventive UDCA on Cox-2 expression in AOM tumors. Cholic acid enhanced Cox-2 upregulation in AOM tumors, whereas UDCA inhibited this increase and concomitantly decreased CCAAT/enhancer binding protein beta (C/EBPbeta), a transcriptional regulator of Cox-2. In HCA-7 colon cancer cells, DCA activated Ras and increased C/EBPbeta and Cox-2 by a mechanism requiring the mitogen-activated protein kinase p38. UDCA inhibited DCA-induced p38 activation and decreased C/EBPbeta and Cox-2 upregulation. Using transient transfections, UDCA inhibited Cox-2 promoter and C/EBP reporter activation by DCA. Transfection with dominant-negative (17)N-Ras abolished DCA-induced p38 activation and C/EBPbeta and Cox-2 upregulation. Taken together, these studies have identified a transcriptional pathway regulating Cox-2 expression involving Ras, p38, and C/EBPbeta that is inhibited by UDCA. These signal transducers are novel targets of UDCA's chemopreventive actions.

Intestinal bile acid physiology and pathophysiology

Bile acids (BAs) have a long established role in fat digestion in the intestine by acting as tensioactives, due to their amphipathic characteristics. BAs are reabsorbed very efficiently by the intestinal epithelium and recycled back to the liver via transport mechanisms that have been largely elucidated. The transport and synthesis of BAs are tightly regulated in part by specific plasma membrane receptors and nuclear receptors. In addition to their primary effect, BAs have been claimed to play a role in gastrointestinal cancer, intestinal inflammation and intestinal ionic transport. BAs are not equivalent in any of these biological activities, and structural requirements have been generally identified. In particular, some BAs may be useful for cancer chemoprevention and perhaps in inflammatory bowel disease, although further research is necessary in this field. This review covers the most recent developments in these aspects of BA intestinal biology.

Bile salts induce resistance to apoptosis through NF-kappaB-mediated XIAP expression

Apoptosis plays a critical role in intestinal mucosal homeostasis. We previously showed that the bile salt taurodeoxycholate has a beneficial effect on the intestinal mucosa through an increase in resistance to apoptosis mediated by nuclear factor (NF)-kappaB. The current study further characterizes the effect of bile salts on intestinal epithelial cell susceptibility to apoptosis and determines if the X-linked inhibitor of apoptosis protein (XIAP) regulates bile salt-induced resistance to apoptosis. Exposure of normal intestinal epithelial cells (IEC-6) to the conjugated bile salts taurodeoxycholate (TDCA) and taurochenodeoxycholate (TCDCA) resulted in an increase in resistance to tumor necrosis factor (TNF)-alpha and cycloheximide (CHX)-induced apoptosis, and NF-kappaB activation. Treatment with TDCA and TCDCA resulted in an increase in XIAP expression. Specific inhibition of NF-kappaB by infection with an adenoviral vector that expresses the IkappaBalpha super-repressor (IkappaBSR) prevented the induction of XIAP expression and the bile salt-mediated resistance to apoptosis. Treatment with the specific XIAP inhibitor Smac also overcame this increase in enterocyte resistance to apoptosis. Bile salts inhibited formation of the active caspase-3 from its precursor procaspase-3. Smac prevented the inhibitory effect of bile salts on caspase-3 activation. These results indicate that bile salts increase intestinal epithelial cell resistance to apoptosis through NF-kappaB-mediated XIAP expression. Bile salt-induced XIAP mediates resistance to TNF-alpha/CHX-induced apoptosis, at least partially, through inhibition of caspase-3 activity. These data support an important beneficial role of bile salts in regulation of mucosal integrity. Decreased enterocyte exposure to luminal bile salts, as occurs during starvation and parenteral nutrition, may have a detrimental effect on mucosal integrity.

Interactions of high amylose starch and deoxycholic acid on gut functions in rats

OBJECTIVE

This study evaluated whether high amylose cornstarch (HAS) could prevent adverse physiologic effects induced by deoxycholic acid (DCA) in the gut of rats.

METHODS

Thirty-two male Sprague-Dawley rats were provided with a low amylose cornstarch (LAS) diet or a 50/50 mixture of LAS and HAS diets for 4 wk; each of these diets was supplemented with 0 or 2 g of DCA per kilogram of diet. Therefore, there were four groups.

RESULTS

Cecal content pH was lower in rats fed the HAS diets compared with rats fed the LAS diets (P < 0.05). Bifidobacteria number in cecal contents, cecal pools of acetate, butyrate, and total short-chain fatty acids were highest in rats fed the HAS diet; moreover, the HAS/DCA diet resulted in increased Bifidobacteria growth and short-chain fatty acid production numerically compared with the LAS/DCA diets (P = 0.06). Production of prostaglandin-E2 in colonic mucosa was highest in rats fed the LAS/DCA diet, and the intake of HAS significantly decreased prostaglandin-E2 levels (P < 0.05).

CONCLUSIONS

In this study, DCA may have inhibited fermentation in the large intestine and increased prostaglandin-E2 production, and concurrent administration of HAS and DCA may have decreased the adverse effects on the gut induced by DCA.

Ursodeoxycholic acid inhibits translocation of protein kinase C in human colonic cancer cell lines

Deoxycholic acid (DCA) has been implicated in colonic carcinogenesis through effects mediated by protein kinase C (PKC) activation. By contrast, ursodeoxycholic acid (UDCA) is reported to reduce colon cancer incidence in ulcerative colitis. The aim of this study was to investigate whether UDCA modulated DCA-induced PKC isoenzyme translocation to its site of activity. HCT116 cells were treated with DCA, UDCA alone or pre-treated with UDCA followed by DCA. Analysis of translocation of endogenous and enhanced green fluorescent protein (EGFP) constructs of PKC isoenzymes was performed. Both DCA and phorbol myristate acetate (PMA) but not UDCA caused translocation of endogenous PKC alpha, epsilon and delta and transfected PKC beta1-, epsilon- and delta-EGFP from cytosol to plasma membrane, reflecting isoenzyme activation. Furthermore, UDCA inhibited DCA-induced translocation of PKC isoenzymes. Inhibition of DCA-induced PKC translocation may be a mechanism for UDCA-mediated chemoprevention of colon carcinogenesis.

Bile salt biotransformations by human intestinal bacteria

Secondary bile acids, produced solely by intestinal bacteria, can accumulate to high levels in the enterohepatic circulation of some individuals and may contribute to the pathogenesis of colon cancer, gallstones, and other gastrointestinal (GI) diseases. Bile salt hydrolysis and hydroxy group dehydrogenation reactions are carried out by a broad spectrum of intestinal anaerobic bacteria, whereas bile acid 7-dehydroxylation appears restricted to a limited number of intestinal anaerobes representing a small fraction of the total colonic flora. Microbial enzymes modifying bile salts differ between species with respect to pH optima, enzyme kinetics, substrate specificity, cellular location, and possibly physiological function. Crystallization, site-directed mutagenesis, and comparisons of protein secondary structure have provided insight into the mechanisms of several bile acid-biotransforming enzymatic reactions. Molecular cloning of genes encoding bile salt-modifying enzymes has facilitated the understanding of the genetic organization of these pathways and is a means of developing probes for the detection of bile salt-modifying bacteria. The potential exists for altering the bile acid pool by targeting key enzymes in the 7alpha/beta-dehydroxylation pathway through the development of pharmaceuticals or sequestering bile acids biologically in probiotic bacteria, which may result in their effective removal from the host after excretion.

Ligand-dependent activation of the epidermal growth factor receptor by secondary bile acids in polarizing colon cancer cells

BACKGROUND

Secondary bile acids such as deoxycholic acid (DCA) are known to promote colorectal cancer (CRC). Increasing evidence suggests that DCA-induced signaling is mediated by activation of the epidermal growth factor receptor (EGFR). We have shown that activation of the EGFR induces up-regulation of cyclooxygenase 2, basolateral release of prostaglandins (PGs), and mitogenesis in a polarizing human colon cancer cell line, HCA-7. The purpose of this study was to determine the mechanism by which DCA activates EGFR in human polarizing CRC cell lines HCA-7 and HCT-8.

METHODS

A primary, non-tumor-promoting bile acid (cholic acid [CA]) and a secondary, tumor-promoting bile acid, DCA, were added to the apical and basolateral compartment of polarized HCA-7 and HCT-8 cells. These cells were pretreated with monoclonal antibody 528, a monoclonal antibody that inhibits ligand binding to EGFR, or with WAY-022, a selective inhibitor of tumor necrosis factor-alpha converting enzyme/a disintegrin and metalloprotease-17 (TACE/ADAM-17), which cleaves amphiregulin (AR) to its mature, soluble form from the basolateral cell membrane. AR levels were measured in the apical and basolateral medium and cell lysates by radioimmunoassay. PGs were measured in the apical and basolateral medium by gas chromatography/mass spectrometry.

RESULTS

Basolateral delivery of DCA, but not CA, preferentially stimulated release of AR into the basolateral medium compared with cell lysates of polarized HCA-7 and HCT-8 cells. Basolateral delivery of DCA resulted in increased basolateral PGE2 levels (P < .05), and this effect was attenuated by pretreatment with monoclonal antibody 528 (P < .05). Inhibiting cell surface cleavage of AR with WAY-022 before DCA treatment reduced AR (P < .05) and PGE2 (P < .05) levels in the basolateral medium.

CONCLUSION

DCA, but not CA, results in compartment-specific, ligand-dependent activation of EGFR and subsequent increased basolateral PGE2 levels. The mechanism of DCA-induced EGFR activation is ligand-dependent and is controlled, at least in part, at the level of AR release from the basolateral cell membrane.

Activation of CFTR by ASBT-mediated bile salt absorption

In cholangiocytes, bile salt (BS) uptake via the apical sodium-dependent bile acid transporter (ASBT) may evoke ductular flow by enhancing cAMP-mediated signaling to the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel. We considered that ASBT-mediated BS uptake in the distal ileum might also modulate intestinal fluid secretion. Taurocholate (TC) induced a biphasic rise in the short circuit current across ileal tissue, reflecting transepithelial electrogenic ion transport. This response was sensitive to bumetanide and largely abrogated in Cftr-null mice, indicating that it predominantly reflects CFTR-mediated Cl- secretion. The residual response in Cftr-null mice could be attributed to electrogenic ASBT activity, as it matched the TC-coupled absorptive Na+ flux. TC-evoked Cl- secretion required ASBT-mediated TC uptake, because it was blocked by a selective ASBT inhibitor and was restricted to the distal ileum. Suppression of neurotransmitter or prostaglandin release, blocking of the histamine H1 receptor, or pretreatment with 5-hydroxytryptamine did not abrogate the TC response, suggesting that neurocrine or immune mediators of Cl- secretion are not involved. Responses to TC were retained after carbachol treatment and after permeabilization of the basolateral membrane with nystatin, indicating that BS modulate CFTR channel gating rather than the driving force for Cl- exit. TC-induced Cl- secretion was maintained in cGMP-dependent protein kinase II-deficient mice and only partially inhibited by the cAMP-dependent protein kinase inhibitor H89, suggesting a mechanism of CFTR activation different from cAMP or cGMP signaling. We conclude that active BS absorption in the ileum triggers CFTR activation and, consequently, local salt and water secretion, which may serve to prevent intestinal obstruction in the postprandial state.

Subepithelial myofibroblasts express cyclooxygenase-2 in colorectal tubular adenomas

PURPOSE

Recent data support the hypothesis that the inducible isoform of cyclooxygenase (COX-2) plays a role in the early stages of colonic carcinogenesis and that nonsteroidal anti-inflammatory drugs (NSAIDs) retard the development of colon cancer by modulating COX-2. However, the cell types responsible for producing COX-2 in colorectal adenomas remain a subject of controversy.

EXPERIMENTAL DESIGN

COX-2 expression in normal colonic mucosa (n = 50), hyperplastic polyps (n = 43), sporadic adenomas (n = 67), and invasive colonic adenocarcinoma (n = 39) was studied in formalin-fixed and paraffin-embedded tissue sections from endoscopy biopsy and colonic resection specimens. Immunohistochemistry (avidin-biotin complex technique with double immunolabeling) was used to identify the phenotypes of COX-2-producing cells.

RESULTS

In colorectal adenomas, increased expression of COX-2 was detected and localized to alpha smooth muscle actin ( proportional, variant SMA)-positive subepithelial stromal cells (myofibroblasts) in the periluminal region of the lamina propria in 63 (94%) of 67 cases. In contrast, in normal colonic mucosa and in hyperplastic polyps with intact epithelium, COX-2 expression was found only in macrophages and endothelial cells. In areas in which the surface epithelium was ulcerated in normal mucosa as well as hyperplastic or neoplastic polyps, COX-2 expression was increased in granulation tissue (and present in macrophages, endothelium, and myofibroblasts). In invasive carcinoma, COX-2 expression in myofibroblasts was limited to the adenomatous portion of the tumor and was detected in 62% of cases (n = 39). In addition, focal expression of COX-2 by malignant epithelial cells was observed in 23% of invasive adenocarcinoma.

CONCLUSIONS

These results show that increased COX-2 expression in sporadic adenoma of the colon is common and is localized specifically to subepithelial intestinal myofibroblasts. These findings further support the hypothesis that myofibroblasts are important target cells for NSAID-mediated chemoprevention of colorectal cancer.

Deoxycholic acid inhibits pacemaker currents by activating ATP-dependent K+ channels through prostaglandin E2 in interstitial cells of Cajal from the murine small intestine

1. We investigated the role of deoxycholic acid in pacemaker currents using whole-cell patch-clamp techniques at 30 degrees C in cultured interstitial cells of Cajal (ICC) from murine small intestine. 2. The treatment of ICC with deoxycholic acid resulted in a decrease in the frequency and amplitude of pacemaker currents and increases in resting outward currents. Also, under current clamping, deoxycholic acid produced the hyperpolarization of membrane potential and decreased the amplitude of the pacemaker potentials. 3. These observed effects of deoxycholic acid on pacemaker currents and pacemaker potentials were completely suppressed by glibenclamide, an ATP-sensitive K(+) channel blocker. 4. NS-398, a specific cyclooxygenase-2 (COX-2) inhibitor, significantly inhibited the deoxycholic acid-induced effects. The treatment with prostaglandin E(2) (PGE(2)) led to a decrease in the amplitude and frequency of pacemaker currents and to an increase in resting outward currents, and these observed effects of PGE(2) were blocked by glibenclamide. 5. We next examined the role of deoxycholic acid in the production of PGE(2) in ICC, and found that deoxycholic acid increased PGE(2) production through the induction of COX-2 enzyme activity and its gene expression. 6. The results suggest that deoxycholic acid inhibits the pacemaker currents of ICC by activating ATP-sensitive K(+) channels through the production of PGE(2).

Results of a Phase I Multiple-Dose Clinical Study of Ursodeoxycholic Acid

Background: The hydrophilic bile acid, ursodeoxycholic acid (UDCA), may indirectly protect against colon carcinogenesis by decreasing the overall proportion of the more hydrophobic bile acids, such as deoxycholic acid (DCA), in aqueous phase stool. In the AOM rat model, treatment with UDCA resulted in a significant decrease in adenoma formation and colorectal cancer. It was hypothesized that there is a dose-response relationship between treatment with the more hydrophilic bile acid, UDCA, and a reduction in the proportion of the more hydrophobic bile acid, DCA, in the aqueous stool phase, suggesting the potential of UDCA as a chemopreventive agent. Methods: Eighteen participants were randomized to 300, 600, or 900 mg/day UDCA for 21 days in this multiple-dose, double-blinded study. Seventy-two-hour stool samples were collected pretreatment and on days 18–20 of UDCA treatment for bile acid measurements. Pharmacokinetics were performed and blood bile acids were measured at days 1 and 21 of UDCA treatment. Results: There were no serious adverse events associated with UDCA treatment. There was a dose-response increase in the posttreatment to baseline ratio of UDCA to DCA from the 300 mg/day to the 600 mg/day group, but not between the 600 and the 900 mg/day groups, in both aqueous and solid phase stool. This posttreatment increase was statistically significant in aqueous phase stool for the 300 and 600 mg/day treatment groups (P = 0.038 and P = 0.014, respectively), but was only marginally significant in the 900 mg/day treatment group (P = 0.057). Following the first dose administration, a dose-dependent increase in plasma ursodeoxycholic concentrations was observed in fasting subjects; however, when these levels were measured postprandially following 3 weeks of treatment, the areas under the plasma concentration-time profile (AUC) were not statistically different and remained relatively unchanged over time. Conclusions: UDCA treatment did not decrease the quantity of DCA in fecal water or solids; however, it did decrease the proportion of DCA in fecal water and solids in relation to UDCA. Thus, 3 weeks of UDCA treatment resulted in an overall increase in hydrophilicity of bile acids in the aqueous phase stool, with a peak effect observed with a daily dose of 600 mg/day. Much larger studies are needed to determine the effect of ursodeoxycholic administration on deoxycholic concentration, overall hydrophilicity of stool bile acids, and the long-term effects on intermediate biomarkers of cellular damage.

C-type natriuretic peptide induces human colonic myofibroblast relaxation

Intestinal response to injury requires coordinated regulation of the tension exerted by subepithelial myofibroblasts (SEM). However, the signals governing relaxation of intestinal SEM have not been investigated. Our aim was to test the hypothesis that signal transduction pathways initiated by C-type natriuretic peptide (CNP) induce intestinal SEM relaxation. We directly quantified the effects of CNP on isometric tension exerted by cultured human colonic SEM. We also measured the effects of CNP on cGMP content, myosin regulatory light chain (MLC) phosphorylation, and cytosolic Ca2+ concentration. CNP induced relaxation of SEM within 10 s. By 10 min, relaxation reached a plateau that was sustained for 2 h. CNP-induced relaxation was saturable, with a maximal decrease in tension (51.7 +/- 3.8 dyn) observed at 250 nM. SEM relaxation in response to CNP constituted approximately 23% of total basal tension. CNP increased intracellular cGMP content and reduced MLC phosphorylation. Effects of CNP on cGMP and MLC exhibited the same dose dependence as CNP-induced relaxation. MLC phosphorylation decreased within 2 min of CNP exposure and was sustained for at least 45 min. CNP also stimulated a large transient increase in cytosolic Ca2+ concentration that occurred within 30 s and was nearly complete by 1 min. We also observed that calyculin-A, a potent inhibitor of MLC phosphatase, completely abolished the reduction in MLC phosphorylation induced by CNP. These results suggest that CNP induces intestinal SEM relaxation through cGMP-associated reductions in MLC phosphorylation. Moreover, these findings raise the possibility that CNP plays a role in intestinal wound healing.