Ursodeoxycholic acid protects colon cancer HCT116 cells from deoxycholic acid-induced apoptosis by inhibiting apoptosome formation

Bile acid metabolism and signaling in health and disease: molecular mechanisms and therapeutic targets

Bile acids, once considered mere dietary surfactants, now emerge as critical modulators of macronutrient (lipid, carbohydrate, protein) metabolism and the systemic pro-inflammatory/anti-inflammatory balance. Bile acid metabolism and signaling pathways play a crucial role in protecting against, or if aberrant, inducing cardiometabolic, inflammatory, and neoplastic conditions, strongly influencing health and disease. No curative treatment exists for any bile acid influenced disease, while the most promising and well-developed bile acid therapeutic was recently rejected by the FDA. Here, we provide a bottom-up approach on bile acids, mechanistically explaining their biochemistry, physiology, and pharmacology at canonical and non-canonical receptors. Using this mechanistic model of bile acids, we explain how abnormal bile acid physiology drives disease pathogenesis, emphasizing how ceramide synthesis may serve as a unifying pathogenic feature for cardiometabolic diseases. We provide an in-depth summary on pre-existing bile acid receptor modulators, explain their shortcomings, and propose solutions for how they may be remedied. Lastly, we rationalize novel targets for further translational drug discovery and provide future perspectives. Rather than dismissing bile acid therapeutics due to recent setbacks, we believe that there is immense clinical potential and a high likelihood for the future success of bile acid therapeutics.

The anticancer activity of bile acids in drug discovery and development

Bile acids (BAs) constitute essential components of cholesterol metabolites that are synthesized in the liver, stored in the gallbladder, and excreted into the intestine through the biliary system. They play a crucial role in nutrient absorption, lipid and glucose regulation, and the maintenance of metabolic homeostasis. In additional, BAs have demonstrated the ability to attenuate disease progression such as diabetes, metabolic disorders, heart disease, and respiratory ailments. Intriguingly, recent research has offered exciting evidence to unveil their potential antitumor properties against various cancer cell types including tamoxifen-resistant breast cancer, oral squamous cell carcinoma, cholangiocarcinoma, gastric cancer, colon cancer, hepatocellular carcinoma, prostate cancer, gallbladder cancer, neuroblastoma, and others. Up to date, multiple laboratories have synthesized novel BA derivatives to develop potential drug candidates. These derivatives have exhibited the capacity to induce cell death in individual cancer cell types and display promising anti-tumor activities. This review extensively elucidates the anticancer activity of natural BAs and synthetic derivatives in cancer cells, their associated signaling pathways, and therapeutic strategies. Understanding of BAs and their derivatives activities and action mechanisms will evidently assist anticancer drug discovery and devise novel treatment.

The role of bile acids in carcinogenesis

Bile acids are soluble derivatives of cholesterol produced in the liver that subsequently undergo bacterial transformation yielding a diverse array of metabolites. The bulk of bile acid synthesis takes place in the liver yielding primary bile acids; however, other tissues have also the capacity to generate bile acids (e.g. ovaries). Hepatic bile acids are then transported to bile and are subsequently released into the intestines. In the large intestine, a fraction of primary bile acids is converted to secondary bile acids by gut bacteria. The majority of the intestinal bile acids undergo reuptake and return to the liver. A small fraction of secondary and primary bile acids remains in the circulation and exert receptor-mediated and pure chemical effects (e.g. acidic bile in oesophageal cancer) on cancer cells. In this review, we assess how changes to bile acid biosynthesis, bile acid flux and local bile acid concentration modulate the behavior of different cancers. Here, we present in-depth the involvement of bile acids in oesophageal, gastric, hepatocellular, pancreatic, colorectal, breast, prostate, ovarian cancer. Previous studies often used bile acids in supraphysiological concentration, sometimes in concentrations 1000 times higher than the highest reported tissue or serum concentrations likely eliciting unspecific effects, a practice that we advocate against in this review. Furthermore, we show that, although bile acids were classically considered as pro-carcinogenic agents (e.g. oesophageal cancer), the dogma that switch, as lower concentrations of bile acids that correspond to their serum or tissue reference concentration possess anticancer activity in a subset of cancers. Differences in the response of cancers to bile acids lie in the differential expression of bile acid receptors between cancers (e.g. FXR vs. TGR5). UDCA, a bile acid that is sold as a generic medication against cholestasis or biliary surge, and its conjugates were identified with almost purely anticancer features suggesting a possibility for drug repurposing. Taken together, bile acids were considered as tumor inducers or tumor promoter molecules; nevertheless, in certain cancers, like breast cancer, bile acids in their reference concentrations may act as tumor suppressors suggesting a Janus-faced nature of bile acids in carcinogenesis.

The secondary bile acids, ursodeoxycholic acid and lithocholic acid, protect against intestinal inflammation by inhibition of epithelial apoptosis

Increased epithelial permeability is a key feature of IBD pathogenesis and it has been proposed that agents which promote barrier function may be of therapeutic benefit. We have previously reported the secondary bile acid, ursodeoxycholic acid (UDCA), to be protective in a mouse model of colonic inflammation and that its bacterial metabolism is required for its beneficial effects. The current study aimed to compare the effects of UDCA, LCA, and a non‐metabolizable analog of UDCA, 6‐methyl‐UDCA (6‐MUDCA), on colonic barrier function and mucosal inflammation in a mouse model of colonic inflammation. Bile acids were administered daily to C57Bl6 mice by intraperitoneal injection. Colonic inflammation, induced by addition of DSS (2.5%) to the drinking water, was measured as disease activity index (DAI) and histological score. Epithelial permeability and apoptosis were assessed by measuring FITC‐dextran uptake and caspase‐3 cleavage, respectively. Cecal bile acids were measured by HPLC‐MS/MS. UDCA and LCA, but not 6‐MUDCA, were protective against DSS‐induced increases in epithelial permeability and colonic inflammation. Furthermore, UDCA and LCA inhibited colonic epithelial caspase‐3 cleavage both in DSS‐treated mice and in an in vitro model of cytokine‐induced epithelial injury. HPLC‐MS/MS analysis revealed UDCA administration to increase colonic LCA levels, whereas LCA administration did not alter UDCA levels. UDCA, and its primary metabolite, LCA, protect against intestinal inflammation in vivo, at least in part, by inhibition of epithelial apoptosis and promotion of barrier function. These data suggest that clinical trials of UDCA in IBD patients are warranted.

Ursodeoxycholic acid: a promising therapeutic target for inflammatory bowel diseases?

The secondary bile acid ursodeoxycholic acid (UDCA) has long been known to have medicinal properties. As the therapeutically active component of bear bile, it has been used for centuries in traditional Chinese medicine to treat a range of conditions, while manufactured UDCA has been used for decades in Western medicine to treat cholestatic liver diseases. The beneficial qualities of UDCA are thought to be due to its well-established cytoprotective and anti-inflammatory actions. In addition to its established role in treating liver diseases, UDCA is now under investigation for numerous conditions associated with inflammation and apoptosis, including neurological, ocular, metabolic, and cardiovascular diseases. Here, we review the growing evidence base from in vitro and in vivo models to suggest that UDCA may also have a role to play in the therapy of inflammatory bowel diseases.

A novel ASBT inhibitor, IMB17-15, repressed nonalcoholic fatty liver disease development in high-fat diet-fed Syrian golden hamsters

The manipulation of bile acid (BA) homeostasis by blocking the ileal apical Na⁺-dependent bile salt transporter (ASBT/SLC10A2) may have therapeutic effects in nonalcoholic fatty liver disease. We developed a novel ASBT inhibitor, an N-(3,4-o-dichlorophenyl)-2-(3-trifluoromethoxy) benzamide derivative referred to as IMB17-15, and investigated its therapeutic effects and the molecular mechanisms underlying the effects. Syrian golden hamsters were challenged with high-fat diet (HFD) to induce NAFLD and were subsequently administered 400 mg/kg IMB17-15 by gavage daily for 21 days. Serum, liver, and fecal samples were collected for further analysis. Plasma concentration-time profiles of IMB17-15 were also constructed. The human hepatocyte cell line HL-7702 was treated with Oleic acid (OA) with or without IMB17-15. Western blotting and real-time PCR were used to study the molecular mechanisms of IMB17-15. We found that IMB17-15 inhibited ASBT and subsequently suppressed ileal farnesoid X receptor (FXR) and FXR-activated fibroblast growth factor15/19 (FGF15/19) expression, which reduced the hepatic phosphorylated extracellular regulated protein kinase (ERK) and c-Jun N-terminal kinase (JNK) levels and upregulated the cholesterol 7α-hydroxylase (CYP7A1) activity. Additionally, IMB17-15 stimulated adenosine monophosphate (AMP)-activated protein kinase (AMPKα) phosphorylation and enhanced peroxisome proliferator activated receptor α (PPARα) expression and thus promoted triglyceride (TG) oxidation and high-density lipoprotein cholesterol (HDL-c) metabolism through an ASBT-independent mechanism. In conclusion, a novel ASBT inhibitor known as IMB17-15 protected hamsters against HFD-induced NFALD by manipulating BA and lipid homeostasis. IMB17-15 also reduced lipid deposition in human hepatic cell lines, indicating that it may be useful as a therapy for NAFLD patients.

A novel, protective role of ursodeoxycholate in bile-induced pancreatic ductal injury

We have previously shown that chenodeoxycholic acid (CDCA) strongly inhibits pancreatic ductal HCO3 (-) secretion through the destruction of mitochondrial function, which may have significance in the pathomechanism of acute pancreatitis (AP). Ursodeoxycholic acid (UDCA) is known to protect the mitochondria against hydrophobic bile acids and has an ameliorating effect on cell death. Therefore, our aim was to investigate the effect of UDCA pretreatment on CDCA-induced pancreatic ductal injury. Guinea pig intrainterlobular pancreatic ducts were isolated by collagenase digestion. Ducts were treated with UDCA for 5 and 24 h, and the effect of CDCA on intracellular Ca(2+) concentration ([Ca(2+)]i), intracellular pH (pHi), morphological and functional changes of mitochondria, and the rate of apoptosis were investigated. AP was induced in rat by retrograde intraductal injection of CDCA (0.5%), and the disease severity of pancreatitis was assessed by measuring standard laboratory and histological parameters. Twenty-four-hour pretreatment of pancreatic ducts with 0.5 mM UDCA significantly reduced the rate of ATP depletion, mitochondrial injury, and cell death induced by 1 mM CDCA and completely prevented the inhibitory effect of CDCA on acid-base transporters. UDCA pretreatment had no effect on CDCA-induced Ca(2+) signaling. Oral administration of UDCA (250 mg/kg) markedly reduced the severity of CDCA-induced AP. Our results clearly demonstrate that UDCA 1) suppresses the CDCA-induced pancreatic ductal injury by reducing apoptosis and mitochondrial damage and 2) reduces the severity of CDCA-induced AP. The protective effect of UDCA against hydrophobic bile acids may represent a novel therapeutic target in the treatment of biliary AP.

Modulation of cell metabolic pathways and oxidative stress signaling contribute to acquired melphalan resistance in multiple myeloma cells

Alkylating agents are widely used chemotherapeutics in the treatment of many cancers, including leukemia, lymphoma, multiple myeloma, sarcoma, lung, breast and ovarian cancer. Melphalan is the most commonly used chemotherapeutic agent against multiple myeloma. However, despite a 70-80% initial response rate, virtually all patients eventually relapse due to the emergence of drug-resistant tumour cells. By using global proteomic and transcriptomic profiling on melphalan sensitive and resistant RPMI8226 cell lines followed by functional assays, we discovered changes in cellular processes and pathways not previously associated with melphalan resistance in multiple myeloma cells, including a metabolic switch conforming to the Warburg effect (aerobic glycolysis), and an elevated oxidative stress response mediated by VEGF/IL8-signaling. In addition, up-regulated aldo-keto reductase levels of the AKR1C family involved in prostaglandin synthesis contribute to the resistant phenotype. Finally, selected metabolic and oxidative stress response enzymes were targeted by inhibitors, several of which displayed a selective cytotoxicity against the melphalan-resistant cells and should be further explored to elucidate their potential to overcome melphalan resistance.

Differential regulation of EGFR-MAPK signaling by deoxycholic acid (DCA) and ursodeoxycholic acid (UDCA) in colon cancer

A high-fat diet coincides with increased levels of bile acids. This increase in bile acids, particularly deoxycholic acid (DCA), has been strongly associated with the development of colon cancer. Conversely, ursodeoxycholic acid (UDCA) may have chemopreventive properties. Although structurally similar, DCA and UDCA present different biological and pathological effects in colon cancer progression. The differential regulation of cancer by these two bile acids is not yet fully understood. However, one possible explanation for their diverging effects is their ability to differentially regulate signaling pathways involved in the multistep progression of colon cancer, such as the epidermal growth factor receptor (EGFR)-mitogen-activated protein kinase (MAPK) pathway. This review will examine the biological effects of DCA and UDCA on colon cancer development, as well as the diverging effects of these bile acids on the oncogenic signaling pathways that play a role in colon cancer development, with a particular emphasis on bile acid regulation of the EGFR-MAPK pathway.

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.