Elimination of Na+-dependent bile acid transporter from small intestine by ileum resection increases [correction of increase] colonic tumorigenesis in the rat fed deoxycholic acid

Anti-miR-135/SPOCK1 axis antagonizes the influence of metabolism on drug response in intestinal/colon tumour organoids

Little is known about the role of microRNAs (miRNAs) in rewiring the metabolism within tumours and adjacent non-tumour bearing normal tissue and their potential in cancer therapy. This study aimed to investigate the relationship between deregulated miRNAs and metabolic components in murine duodenal polyps and non-polyp-derived organoids (mPOs and mNPOs) from a double-mutant Apc^MinFbxw7^∆G mouse model of intestinal/colorectal cancer (CRC). We analysed the expression of 373 miRNAs and 12 deregulated metabolic genes in mPOs and mNPOs. Our findings revealed miR-135b might target Spock1. Upregulation of SPOCK1 correlated with advanced stages of CRCs. Knockdown of miR-135b decreased the expression level of SPOCK1, glucose consumption and lactic secretion in CRC patient-derived tumours organoids (CRC tPDOs). Increased SPOCK1 induced by miR-135b overexpression promoted the Warburg effect and consequently antitumour effect of 5-fluorouracil. Thus, combination with miR-135b antisense nucleotides may represent a novel strategy to sensitise CRC to the chemo-reagent based treatment.

Inflammatory Bowel Disease and Primary Sclerosing Cholangitis: A Review of the Phenotype and Associated Specific Features

Primary sclerosing cholangitis (PSC) is a chronic, progressive cholestatic disease that is associated with inflammatory bowel disease (IBD) in approximately 70% of cases. Although the pathogenesis is still unknown for both diseases, there is increasing evidence to indicate that they share a common underlying predisposition. Herein, we review the epidemiology, diagnosis, disease pathogenesis, and specific clinical features of the PSC-IBD phenotype. Patients with PSC-IBD have a distinct IBD phenotype with an increased incidence of pancolitis, backwash ileitis, and rectal sparing. Despite often having extensive colonic involvement, these patients present with mild intestinal symptoms or are even asymptomatic, which can delay the diagnosis of IBD. Although the IBD phenotype has been well characterized in PSC patients, the natural history and disease behavior of PSC in PSC-IBD patients is less well defined. There is conflicting evidence regarding the course of IBD in PSC-IBD patients who receive liver transplantation and their risk of recurrent PSC. IBD may also be associated with an increased risk of cholangiocarcinoma in PSC patients. Overall, the PSC-IBD population has an increased risk of developing colorectal neoplasia compared to the conventional IBD population. Lifelong annual surveillance colonoscopy is currently recommended.

The role of bile acids in reducing the metabolic complications of obesity after bariatric surgery: a systematic review

BACKGROUND

Bariatric surgery is currently the most efficacious treatment for obesity and its associated metabolic co-morbidities, such as diabetes. The metabolic improvements occur through both weight-dependent and weight-independent mechanisms. Bile acids (BAs) have emerged as key signalling molecules that have a central role in modulating many of the physiological effects seen after bariatric surgery. This systematic review assesses the evidence from both human and animal studies for the role of BAs in reducing the metabolic complications of obesity following bariatric surgery.

METHODS

We conducted a systematic search of Medline and Embase databases to identify all articles investigating the role of BAs in mediating the metabolic changes observed following bariatric surgery in both animal and human studies. Boolean logic was used with relevant search terms, including the following MeSH terms: 'bile acids and salts', 'bariatric surgery', 'metabolic surgery', 'gastrointestinal tract/surgery' and 'obesity/surgery'.

RESULTS

Following database searches (n=1197), inclusion from bibliography searches (n=2) and de-duplication (n=197), 1002 search results were returned. Of these, 132 articles were selected for full-text review, of which 38 articles were deemed relevant and included in the review. The findings support the effects of BAs on satiety, lipid and cholesterol metabolism, incretins and glucose homoeostasis, energy metabolism, gut microbiota and endoplasmic reticulum stress following bariatric surgery. Many of these metabolic effects are modulated through the BA receptors FXR and TGR5. We also explore a possible link between BAs and carcinogenesis following bariatric surgery.

CONCLUSIONS

Overall there is good evidence to support the role of BAs in the metabolic effects of bariatric surgery through the above mechanisms. BAs could serve as a novel therapeutic pharmacological target for the treatment of obesity and its associated co-morbidities.

Upregulation of bile acid receptor TGR5 and nNOS in gastric myenteric plexus is responsible for delayed gastric emptying after chronic high-fat feeding in rats

Chronic high-fat feeding is associated with functional dyspepsia and delayed gastric emptying. We hypothesize that high-fat feeding upregulates gastric neuronal nitric oxide synthase (nNOS) expression, resulting in delayed gastric emptying. We propose this is mediated by increased bile acid action on bile acid receptor 1 (TGR5) located on nNOS gastric neurons. To test this hypothesis, rats were fed regular chow or a high-fat diet for 2 wk. Rats fed the high-fat diet were subjected to concurrent feeding with oral cholestyramine or terminal ileum resection. TGR5 and nNOS expression in gastric tissue was measured by immunohistochemistry, PCR, and Western blot. Gastric motility was assessed by organ bath and solid-phase gastric emptying studies. The 2-wk high-fat diet caused a significant increase in neurons coexpressing nNOS and TGR5 in the gastric myenteric plexus and an increase in nNOS and TGR5 gene expression, 67 and 111%, respectively. Enhanced nonadrenergic, noncholinergic (NANC) relaxation, deoxycholic acid (DCA)-induced inhibition in fundic tissue, and a 26% delay in gastric emptying accompanied these changes. A 24-h incubation of whole-mount gastric fundus with DCA resulted in increased nNOS and TGR5 protein expression, 41 and 37%, respectively. Oral cholestyramine and terminal ileum resection restored the enhanced gastric relaxation, as well as the elevated nNOS and TGR5 expression evoked by high-fat feeding. Cholestyramine also prevented the delay in gastric emptying. We conclude that increased levels of circulatory bile acids induced by high-fat feeding upregulate nNOS and TGR5 expression in the gastric myenteric plexus, resulting in enhanced NANC relaxation and delayed gastric emptying.

Staurosporine synergistically potentiates the deoxycholate-mediated induction of COX-2 expression

Colorectal cancer is a major cause of cancer‐related death in western countries, and thus there is an urgent need to elucidate the mechanism of colorectal tumorigenesis. A diet that is rich in fat increases the risk of colorectal tumorigenesis. Bile acids, which are secreted in response to the ingestion of fat, have been shown to increase the risk of colorectal tumors. The expression of cyclooxygenase (COX)‐2, an inducible isozyme of cyclooxygenase, is induced by bile acids and correlates with the incidence and progression of cancers. In this study, we investigated the signal transduction pathways involved in the bile‐acid‐mediated induction of COX‐2 expression. We found that staurosporine (sts), a potent protein kinase C (PKC) inhibitor, synergistically potentiated the deoxycholate‐mediated induction of COX‐2 expression. Sts did not increase the stabilization of COX‐2 mRNA. The sts‐ and deoxycholate‐mediated synergistic induction of COX‐2 expression was suppressed by a membrane‐permeable Ca²⁺ chelator, a phosphoinositide 3‐kinase inhibitor, a nuclear factor‐κB pathway inhibitor, and inhibitors of canonical and stress‐inducible mitogen‐activated protein kinase pathways. Inhibition was also observed using PKC inhibitors, suggesting the involvement of certain PKC isozymes (η, θ, ι, ζ, or μ). Our results indicate that sts exerts its potentiating effects via the phosphorylation of p38. However, the effects of anisomycin did not mimic those of sts, indicating that although p38 activation is required, it does not enhance deoxycholate‐induced COX‐2 expression. We conclude that staurosporine synergistically enhances deoxycholate‐induced COX‐2 expression in RCM‐1 colon cancer cells.

e12143

The expression of COX‐2, an inducible isozyme of cyclooxygenase, correlates with the incidence and progression of cancers, and bile acids have been shown to induce COX‐2 expression. We investigated the signal transduction pathways involved in the bile‐acid‐mediated induction of COX‐2 expression, and we found that staurosporine, a potent PKC inhibitor, synergistically potentiated the deoxycholate‐mediated induction of COX‐2 expression. Staurosporine exerted its potentiating effects via the phosphorylation of p38, and the involvement of certain PKC isozymes was suggested.

Importance of uncharged polar residues and proline in the proximal two-thirds (Pro107-Ser128) of the highly conserved region of mouse ileal Na+-dependent bile acid transporter, Slc10a2, in transport activity and cellular expression

Background

SLC10A2-mediated reabsorption of bile acids at the distal end of the ileum is the first step in enterohepatic circulation. Because bile acids act not only as detergents but also as signaling molecules in lipid metabolism and energy production, SLC10A2 is important as the key transporter for understanding the in vivo kinetics of bile acids. SLC10A family members and the homologous genes of various species share a highly conserved region corresponding to Gly¹⁰⁴–Pro¹⁴² of SLC10A2. The functional importance of this region has not been fully elucidated.

Results

To elucidate the functional importance of this region, we previously performed mutational analysis of the uncharged polar residues and proline in the distal one-third (Thr¹³⁰–Pro¹⁴²) of the highly conserved region in mouse Slc10a2. In this study, proline and uncharged polar residues in the remaining two-thirds of this region in mouse Slc10a2 were subjected to mutational analysis, and taurocholic acid uptake and cell surface localization were examined. Cell surface localization of Slc10a2 is necessary for bile acid absorption. Mutants in which Asp or Leu were substituted for Pro¹⁰⁷ (P107N or P107L) were abundantly expressed, but their cell surface localization was impaired. The S126A mutant was completely impaired in cellular expression. The T110A and S128A mutants exhibited remarkably enhanced membrane expression. The S112A mutant was properly expressed at the cell surface but transport activity was completely lost. Replacement of Tyr¹¹⁷ with various amino acids resulted in reduced transport activity. The degree of reduction roughly depended on the van der Waals volume of the side chains.

Conclusions

The functional importance of proline and uncharged polar residues in the highly conserved region of mouse Slc10a2 was determined. This information will contribute to the design of bile acid-conjugated prodrugs for efficient drug delivery or SLC10A2 inhibitors for hypercholesterolemia treatment.

Review article: colorectal neoplasia in patients with primary sclerosing cholangitis and inflammatory bowel disease

BACKGROUND

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease strongly associated with inflammatory bowel disease (IBD). IBD patients diagnosed with PSC have an increased risk of colorectal dysplasia and cancer.

AIMS

To review the available evidence regarding colorectal neoplasia epidemiology, preventive strategies and outcomes in patients with PSC and IBD, and to advance some hypotheses regarding possible mechanisms involved in cancer pathogenesis in these patients.

METHODS

A PubMed search was conducted for the English language publications with predetermined search criteria. Reference lists from studies selected were manually searched to identify further relevant reports. Relevant manuscripts considering colorectal neoplasia in patients with PSC-IBD were selected.

RESULTS

Primary sclerosing cholangitis increases the risk of colorectal neoplasia in patients with ulcerative colitis; fewer data are available for Crohn's disease. PSC-IBD patients tend to be younger at diagnosis of IBD and at diagnosis of colorectal cancer. Colorectal cancer in PSC-IBD patients predominates in the right colon. The increased risk of neoplasia is maintained after liver transplant and proctocolectomy. The role of ursodeoxycholic acid as a chemopreventive agent is controversial. The mechanisms underlying increased risk of colorectal neoplasia in these patients remain unknown.

CONCLUSIONS

A more comprehensive understanding of the mechanisms involved in colorectal neoplasia development in PSC-IBD patients is needed. Until then, early cancer detection through enrolment in surveillance programmes is the only available strategy to decrease cancer risk.

Mutational analysis of uncharged polar residues and proline in the distal one-third (Thr130-Pro142) of the highly conserved region of mouse Slc10a2

Solute carrier family member 2 (SLC10A2) reabsorbs bile acids at the distal terminus of the ileum in an Na(+)-dependent manner. Alignment of deduced amino acid sequences of SLC10 family members and homologous genes in various species revealed a highly conserved region that corresponds to Gly(104)-Pro(142) of SLC10A2. To elucidate the functional importance of this region, uncharged polar residues and Pro in the distal one-third of this region in mouse Slc10a2 (mSlc10a2) were submitted to mutational analysis, and taurocholic acid uptake and cell surface localization were evaluated. In addition to mutations that abolished almost all of the transport activity with and without cellular localization failure (P142V and T130A respectively), a mutation that perhaps affected affinity for taurocholic acid was identified (T134A). These results suggest that the highly conserved region contains residues involved in the substrate interaction, function, and cellular localization of mSlc10a2.

Estimation of the potential antitumor activity of microencapsulated Lactobacillus acidophilus yogurt formulation in the attenuation of tumorigenesis in Apc(Min/+) mice

There is a strong correlation between orally administered probiotics and suppression of the low-grade inflammation that can lead to restoration of normal local immune functions. We studied the potential immunomodulatory and antitumorigenic properties of microencapsulated probiotic bacterial cells in a yogurt formulation in Min mice carrying a germline APC mutation. Daily oral administration of microencapsulated Lactobacillus acidophilus bacterial cells in the yogurt formulation mice resulted in significant suppression of colon tumor incidence, tumor multiplicity, and reduced tumor size. Results show that oral administration of microencapsulated L. acidophilus contributed to the stabilization of animal body weight and decreased the release of bile acids. Histopathological analyses revealed fewer adenomas in treated versus untreated animals. Furthermore, treated animals exhibited fewer gastrointestinal intra-epithelial neoplasias with a lower grade of dysplasia in detected tumors. Results suggest that oral administration of microencapsulated probiotic L. acidophilus exerts anti-tumorous activity, which consequently leads to reduced tumor outcome.

Deoxycholic acid promotes the growth of colonic aberrant crypt foci

AKR/J mice are resistant to the tumorigenic properties of the colon carcinogen, azoxymethane (AOM). Following AOM exposure, limited numbers of preneoplastic lesions, referred to as aberrant crypt foci (ACF), are formed in the colon, and their progression to tumors rarely occurs. To determine whether genetic resistance can be overcome by exposure to a dietary tumor promoter, AOM-exposed AKR/J mice were fed a diet containing 0.25% deoxycholic acid (DCA). DCA exposure was begun 1 wk prior to or 1 wk after tumor initiation with AOM. Mice placed on the DCA diet prior to AOM treatment developed a significantly higher multiplicity of ACF compared to AOM-exposed mice fed a control diet (15.50 +/- 0.96 vs. 6.17 +/- 0.48, respectively; P < 0.05). When DCA exposure was begun after AOM treatment (post-initiation), ACF formation was further enhanced (34.00 +/- 1.22). Interestingly, increased numbers of ACF were associated with the presence of nuclear beta-catenin, assessed by immunohistochemistry. While approximately 33% of ACF from mice exposed to DCA prior to AOM treatment contained positive nuclear beta-catenin staining, approximately 77% of ACF from mice fed DCA after AOM were positive. Accumulation of nuclear beta-catenin was not associated with a loss of E-cadherin from the plasma membrane, although loss of APC staining was a consistent feature of most AOM-induced ACF, regardless of DCA exposure. These results demonstrate that exposure to DCA, an important digestive component, is sufficient to sensitize the resistant AKR/J colon to formation of high-grade dysplasia, and that nuclear translocation of beta-catenin may play an important role in this process.

Orthotopic transplantation of intestinal mucosal organoids in rodents

BACKGROUND

Orthotopic transplantation of intestinal mucosal organoids that contain putative mucosal stem cells serves as an important step toward implementing intestinal gene therapy and treatment for malabsorption syndromes in animals and humans. We hypothesized that intestinal mucosal organoids can be transplanted along the axis of the small bowel giving rise to a neomucosa expressing proteins of its donor origin.

METHODS

Epithelial organoids were harvested from neonatal mice or rat small intestine with the use of a combination of enzymatic digestion with dispase and collagenase, and gravity sedimentation. In adult syngeneic recipients, a 7-cm segment of midjejunum was isolated, leaving its vascular pedicle intact. The remaining proximal and distal segments were anastomosed to restore intestinal continuity. The isolated segments were randomly subjected to surgical or chemical mucosectomy with a chelator solution for 30, 45, or 60 minutes and then compared. Histologic examination was used to confirm the presence of enterocytes, goblet cells, enteroendocrine cells, and Paneth cells in the neomucosal segments. To confirm the presence of ileal bile acid transporter (IBAT) gene message and function, we measured sodium-dependent bile acid uptake and IBAT-messenger RNA. Immunohistochemical examination using anti-IBAT antibodies was performed to demonstrate the expression of IBAT in the neomucosal segments. Experiments were repeated in a murine model transgenic for the green fluorescent protein to verify donor origin of the engrafted mucosa expressing IBAT.

RESULTS

The area of peak IBAT function was found to be located in the terminal ileum. Organoid units harvested from this region were capable of generating a small-bowel neoileal mucosa after being seeded into the jejunum. This mucosa was histologically confirmed to differentiate into all 4 intestinal lineages and to express IBAT signal, confirming its donor-derived origin. Optimal engraftment of mucosa expressing the IBAT protein was found in isolated jejunal segments debrided for 45 minutes. Sodium-dependent bile acid uptake was 5-fold higher in the neoileum, compared with the jejunum. IBAT-mRNA levels in the neoileum were 18-100-fold higher than those in the jejunum. Areas of green fluorescent protein-positive mucosa stained positively with anti-IBAT antibody in adjacent sections, suggesting that the regenerated mucosa is from transplanted ileal stem cells.

CONCLUSIONS

Orthotopic transplantation of epithelial organoids containing ileal stem cells was used to generate a neoileal mucosa that expressed all 4 intestinal lineages along with a new zone of active bile acid uptake and IBAT expression in a recipient jejunal segment.

Characteristics of apoptosis in HCT116 colon cancer cells induced by deoxycholic acid

Hydrophobic bile acids induce apoptosis in both colon cancer cells and hepatocytes. The mechanism by which colon cancer cells respond to bile acids is thought to be different from that of hepatocytes. Therefore, we investigated the characteristics of apoptosis in colon cancer cell line HCT116. Hydrophobic bile acids, i.e., deoxycholic acid (DCA), and chenodeoxycholic acid, induced apoptosis in HCT116 cells. Apoptotic indications were detectable at as early as 30 min and the extent increased in time- and concentration-dependent manners. SDS and a hydrophilic bile acid, cholic acid, did not induce apoptosis even at cytotoxic concentrations. Pretreatment with cycloheximide failed to inhibit apoptosis, suggesting that protein synthesis is not involved in the apoptotic response. Release of cytochrome c from mitochondria and activation of caspase-9 were detectable after 5 and 10 min, respectively, whereas remarkable activation of Bid was not detected. Ursodeoxycholic acid (UDCA) protected HCT116 cells from DCA-induced apoptosis but a preincubation period of > or =5 h was required. Nevertheless, UDCA did not inhibit cytochrome c release from mitochondria. Our results indicate that hydrophobic bile acids induce apoptosis in HCT116 cells by releasing cytochrome c from mitochondria via an undefined but specific mechanism, and that UDCA protects HCT116 cells by acting downstream of cytochrome c release.

Treatment of bile acid malabsorption using ileal stem cell transplantation

BACKGROUND

We hypothesized that ileal stem cell clusters transplanted into a segment of jejunum can be used to treat bile acid malabsorption.

STUDY DESIGN

In adult Lewis rats, a 15-cm segment of jejunum was isolated with its blood circulation left intact and partially stripped of enterocytes using luminal high-velocity perfusions with 3mmol/L ethylenediamine tetra-acetic acid solutions. Continuity was restored by anastomosing the proximal and distal gut. Ileal stem cell clusters were harvested from neonatal Lewis rats and transplanted into the stripped segments to generate a "neoileum." After 4weeks, recipients underwent resection of the native ileum, and the isolated neoileum was anastomosed in its place. After an additional 4weeks, a 48-hour stool collection was performed. The engrafted segment was harvested for taurocholate uptake studies, ileal bile acid transporter (IBAT) protein by immunohistomorphometry, and IBAT mRNA quantitation by reverse transcription polymerease chain reaction. Data were analyzed by ANOVA/t-test. Rats undergoing ileectomy, jejunectomy, or sham operations served as controls.

RESULTS

Total bile acid loss in the stool was markedly lower in rats with a neoileum compared with rats with an ileectomy (p < 0.001). Total taurocholate uptake was notably increased in the neoileum compared with the jejunum (p < 0.001). IBAT protein signal intensity was considerably higher in the neoileum compared with jejunum (p < 0.001). IBAT mRNA amounts in the neoileal group were comparable with those in normal rat ileum and were considerably higher (p = 0.003) than in the jejunum.

CONCLUSIONS

Ileal stem cell clusters were used to establish a new zone of bile acid uptake and IBAT expression in a jejunal segment. This neoileum eliminated loss of bile acids in the stool after ileectomy. This is the first time that transplantation of intestinal stem cell clusters has been shown to correct a clinical malabsorption syndrome.

Intestinal bile acid transport: biology, physiology, and pathophysiology

Intestinal reabsorption of bile salts plays a crucial role in human health and disease. This process is primarily localized to the terminal ileum and is mediated by a 48-kd sodium-dependent bile acid cotransporter (SLC10A2 = ASBT). ASBT is also expressed in renal tubule cells, cholangiocytes, and the gallbladder. Exon skipping leads to a truncated version of ASBT, which sorts to the basolateral surface and mediates efflux of bile salts. Inherited mutation of ASBT leads to congenital diarrhea secondary to bile acid malabsorption. Partial inhibition of ASBT may be useful in the treatment of hypercholesterolemia and intrahepatic cholestasis. During normal development in the rat ileum, ASBT undergoes a biphasic pattern of expression with a prenatal onset, postnatal repression, and reinduction at the time of weaning. The bile acid responsiveness of the ASBT gene is not clear and may be dependent on both the experimental model used and the species being investigated. Future studies of the transcriptional and posttranscriptional regulation of the ASBT gene and analysis of ASBT knockout mice will provide further insight into the biology, physiology, and pathophysiology of intestinal bile acid transport.

Non-involvement of the K-ras mutation in colon carcinogenesis promoted by dietary deoxycholate in azoxymethane-treated rats

Fisher-344 rats, whose ileum or jejunum had been surgically removed to change the influx of bile acids into the colon, were intraperitoneally administered with azoxymethane and fed on a diet containing deoxycholate for 39 weeks to induce colon cancer. Fecal bile acids in the ileum-resected group were 1.5-times and serum bile acids were about half of those in the jejunum-resected group. As a result, the incidence and number of tumors were higher in the ileum-resected group. In the total of 59 colon tumors (40 were in the ileum-resected group and 19 in the jejunum-resected group), 56 were carcinomas, including two well-differentiated invasive and two mucinous carcinomas found in the ileum-resected rats. However, only three carcinomas, two invasive and one non-invasive, had the K-ras mutation. These results demonstrate that the K-ras mutation was not essentially involved in deoxycholate-promoted colon carcinogenesis.