Portal vein bile acids in patients with severe inflammatory bowel disease

Bile acid signaling in the regulation of whole body metabolic and immunological homeostasis

Bile acids (BAs) play a crucial role in nutrient absorption and act as key regulators of lipid and glucose metabolism and immune homeostasis. Through the enterohepatic circulation, BAs are synthesized, metabolized, and reabsorbed, with a portion entering the vascular circulation and distributing systemically. This allows BAs to interact with receptors in all major organs, leading to organ-organ interactions that regulate both local and global metabolic processes, as well as the immune system. This review focuses on the whole-body effects of BA-mediated metabolic and immunological regulation, including in the brain, heart, liver, intestine, eyes, skin, adipose tissue, and muscle. Targeting BA synthesis and receptor signaling is a promising strategy for the development of novel therapies for various diseases throughout the body.

The Potential of Bile Acids as Biomarkers for Metabolic Disorders

Bile acids (BAs) are well known to facilitate the absorption of dietary fat and fat-soluble molecules. These unique steroids also function by binding to the ubiquitous cell membranes and nuclear receptors. As chemical signals in gut-liver axis, the presence of metabolic disorders such as nonalcoholic fatty liver disease (NAFLD), type 2 diabetes mellitus (T2DM), and even tumors have been reported to be closely related to abnormal levels of BAs in the blood and fecal metabolites of patients. Thus, the gut microbiota interacting with BAs and altering BA metabolism are critical in the pathogenesis of numerous chronic diseases. This review intends to summarize the mechanistic links between metabolic disorders and BAs in gut-liver axis, and such stage-specific BA perturbation patterns may provide clues for developing new auxiliary diagnostic means.

The Gut Microbiota-Bile Acids-TGR5 Axis Mediates Eucommia ulmoides Leaf Extract Alleviation of Injury to Colonic Epithelium Integrity

Eucommia ulmoides leaves (EL) are rich in phenolic acids and flavonoids, showing enhancing intestinal health effects. The intestinal microbiota-bile acid axis plays important roles in the occurrence and recovery of inflammatory bowel disease (IBD). However, whether EL extract (ELE) has regulatory effects on the intestinal microbiota, bile acid metabolism, and IBD is still unclear. To fill this gap, 2% dextran sulfate sodium (DSS)-induced mild IBD in a C57BL/6J mouse model that was treated with 200 or 400 mg/kg (intake dose/body weight) ELE was used. Oral ELE supplementation alleviated DSS-induced shortening of colon and colonic epithelial injury. Compared with the DSS group, ELE supplementation significantly decreased Toll-like receptor 4 (TLR4) and interlukin-6 (IL-6) and increased occludin and claudin-1 mRNA expression level in the colon (p < 0.05). Combined 16S rRNA gene sequencing and targeted metabolomic analyses demonstrated that ELE significantly improved the diversity and richness of the intestinal microbiota, decreased the abundance of Bacteroidaceae, and increased Akkermansiaceae and Ruminococcaceae abundance (p < 0.05) compared with DSS-induced IBD mice. Moreover, ELE significantly increased the serum contents of deoxycholic acid (DCA) and tauroursodeoxycholic acid (TUDCA), which were highly positively correlated with Akkermansia and unidentified_Ruminococccaceae relative to the DSS group. We then found that ELE increased Takeda G-protein coupled receptor 5 (TGR5), claudin-1, and occludin mRNA expression levels in the colon. In the Caco-2 cell model, we confirmed that activation of TGR5 improved the reduction in transepithelial electoral resistance (TEER) and decreased the permeability of FITC-dextran on monolayer cells induced by LPS (p < 0.05). siRNA interference assays showed that the decrease in TGR5 expression led to the decrease in TEER, an increase in FITC-dextran permeability, and a decrease in claudin-1 protein expression in Caco-2 cells. In summary, ELE alleviated IBD by influencing the intestinal microbiota structure and composition of bile acids, which in turn activated the colonic TGR5 gene expression in the colon and promoted the expression of tight junction proteins. These findings provide new insight for using ELE as a functional food with adjuvant therapeutic effects in IBD.

Bile acids in glucose metabolism and insulin signalling - mechanisms and research needs

Of all the novel glucoregulatory molecules discovered in the past 20 years, bile acids (BAs) are notable for the fact that they were hiding in plain sight. BAs were well known for their requirement in dietary lipid absorption and biliary cholesterol secretion, due to their micelle-forming properties. However, it was not until 1999 that BAs were discovered to be endogenous ligands for the nuclear receptor FXR. Since that time, BAs have been shown to act through multiple receptors (PXR, VDR, TGR5 and S1PR2), as well as to have receptor-independent mechanisms (membrane dynamics, allosteric modulation of N-acyl phosphatidylethanolamine phospholipase D). We now also have an appreciation of the range of physiological, pathophysiological and therapeutic conditions in which endogenous BAs are altered, raising the possibility that BAs contribute to the effects of these conditions on glycaemia. In this Review, we highlight the mechanisms by which BAs regulate glucose homeostasis and the settings in which endogenous BAs are altered, and provide suggestions for future research.

Interaction of gut microbiota with bile acid metabolism and its influence on disease states

Primary bile acids serve important roles in cholesterol metabolism, lipid digestion, host-microbe interactions, and regulatory pathways in the human host. While most bile acids are reabsorbed and recycled via enterohepatic cycling, ∼5% serve as substrates for bacterial biotransformation in the colon. Enzymes involved in various transformations have been characterized from cultured gut bacteria and reveal taxa-specific distribution. More recently, bioinformatic approaches have revealed greater diversity in isoforms of these enzymes, and the microbial species in which they are found. Thus, the functional roles played by the bile acid-transforming gut microbiota and the distribution of resulting secondary bile acids, in the bile acid pool, may be profoundly affected by microbial community structure and function. Bile acids and the composition of the bile acid pool have historically been hypothesized to be associated with several disease states, including recurrent Clostridium difficile infection, inflammatory bowel diseases, metabolic syndrome, and several cancers. Recently, however, emphasis has been placed on how microbial communities in the dysbiotic gut may alter the bile acid pool to potentially cause or mitigate disease onset. This review highlights the current understanding of the interactions between the gut microbial community, bile acid biotransformation, and disease states, and addresses future directions to better understand these complex associations.

Sensitization to autoimmune hepatitis in group VIA calcium-independent phospholipase A2-null mice led to duodenal villous atrophy with apoptosis, goblet cell hyperplasia and leaked bile acids

Chronic bowel disease can co-exist with severe autoimmune hepatitis (AIH) in an absence of primary sclerosing cholangitis. Genetic background may contribute to this overlap syndrome. We previously have shown that the deficiency of iPLA2β causes an accumulation of hepatocyte apoptosis, and renders susceptibility for acute liver injury. We here tested whether AIH induction in iPLA2β-null mice could result in intestinal injury, and whether bile acid metabolism was altered. Control wild-type (WT) and female iPLA2β-null (iPLA2β(-/-)) mice were intravenously injected with 10mg/kg concanavalinA (ConA) or saline for 24h. ConA treatment of iPLA2β(-/-) mice caused massive liver injury with increased liver enzymes, fibrosis, and necrosis. While not affecting WT mice, ConA treatment of iPLA2β(-/-) mice caused severe duodenal villous atrophy concomitant with increased apoptosis, cell proliferation, globlet cell hyperplasia, and endotoxin leakage into portal vein indicating a disruption of intestinal barrier. With the greater extent than in WT mice, ConA treatment of iPLA2β(-/-) mice increased jejunal expression of innate response cytokines CD14, TNF-α, IL-6, and SOCS3 as well as chemokines CCL2 and the CCL3 receptor CCR5. iPLA2β deficiency in response to ConA-induced AIH caused a significant decrease in hepatic and biliary bile acids, and this was associated with suppression of hepatic Cyp7A1, Ntcp and ABCB11/Bsep and upregulation of intestinal FXR/FGF15 mRNA expression. The suppression of hepatic Ntcp expression together with the loss of intestinal barrier could account for the observed bile acid leakage into peripheral blood. Thus, enteropathy may result from acute AIH in a susceptible host such as iPLA2β deficiency.

The profile of bile acids and their sulfate metabolites in human urine and serum

The role of sulfation in ameliorating the hepatotoxicity of bile acids (BAs) in humans remains unknown due to the lack of proper analytical methods to quantify individual BAs and their sulfate metabolites in biological tissues and fluids. To this end, a simple and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated to characterize the detailed BA profile in human urine and serum. The limit of quantification was 1ng/mL and baseline separation of all analytes was achieved within in a run time of 32min. The method was validated over the dynamic range of 1-1000ng/mL. The LC-MS/MS method was more accurate, precise, and selective than the commercially available kits for the quantification of sulfated and unsulfated BAs, and the indirect quantification of individual sulfated BAs after solvolysis. The LC-MS/MS method was applied to characterize the BA profile in urine and serum of healthy subjects. Thirty three percent of serum BAs were sulfated, whereas 89% of urinary BAs existed in the sulfate form, indicating the role of sulfation in enhancing the urinary excretion of BAs. The percentage of sulfation of individual BAs increased with the decrease in the number of hydroxyl groups indicating the role of sulfation in the detoxification of the more hydrophobic and toxic BA species. Eighty percent of urinary BAs and 55% of serum BAs were present in the glycine-amidated form, whereas 8% of urinary BAs and 13% of serum BAs existed in the taurine-amidated form.

Bile Acid sulfation: a pathway of bile acid elimination and detoxification

Sulfotransferase-2A1 catalyzes the formation of bile acid-sulfates (BA-sulfates). Sulfation of BAs increases their solubility, decreases their intestinal absorption, and enhances their fecal and urinary excretion. BA-sulfates are also less toxic than their unsulfated counterparts. Therefore, sulfation is an important detoxification pathway of BAs. Major species differences in BA sulfation exist. In humans, only a small proportion of BAs in bile and serum are sulfated, whereas more than 70% of BAs in urine are sulfated, indicating their efficient elimination in urine. The formation of BA-sulfates increases during cholestatic diseases. Therefore, sulfation may play an important role in maintaining BA homeostasis under pathologic conditions. Farnesoid X receptor, pregnane X receptor, constitutive androstane receptor, and vitamin D receptor are potential nuclear receptors that may be involved in the regulation of BA sulfation. This review highlights current knowledge about the enzymes and transporters involved in the formation and elimination of BA-sulfates, the effect of sulfation on the pharmacologic and toxicologic properties of BAs, the role of BA sulfation in cholestatic diseases, and the regulation of BA sulfation.

Effect of mesalazine, metronidazole and gentamicin on bacterial translocation in experimental colitis

BACKGROUND AND AIM

In inflammatory bowel disease it has been established that enteric microorganisms are present in the final stage of the active inflammatory process. The purpose of the present study was to investigate the effects of mesalazine, and metronidazole-gentamicin combination, on bacterial translocation in an animal colitis model.

METHODS

Fifty rats were stratified into five groups. The control group (group NC) was given only 2 mL saline enema and the remaining four groups were given 2 mL acetic acid enema. Group CC was the diseased control group. The treatment regimens started on the fifth day: mesalazine enema in group MesC, metronidazole-gentamicin in group MGC, and mesalazine + metronidazole + gentamicin in group MesMGC. After death on day 10, 2.5-cm colonic segments from all groups were weighed separately. In all rats, histopathological scoring was done, and samples from feces, blood, liver and spleen underwent microbiological analyses.

RESULTS

For all diseased rats, both mean weight loss and colonic segment weight/bodyweight ratio was significantly higher than that in the sham group. As compared with other groups, body and colonic segment changes as well as histopathological scoring in rats receiving mesalazine enema either solely or in combination with the antibiotics were lower. No bacterial growth was found in the blood, liver and spleen of the rats in the control group while enteric bacteria, mainly Escherichia coli (35%) were the most common bacteria translocated to that in the latter. Antibiotic combination, alone or in combination with mesalazine was effective in reducing the bacterial translocation while mesalazine administration did not properly influence its regression.

CONCLUSIONS

Gram-negative enteric bacteria, predominantly E. coli, was the most common bacteria isolated in bacterial translocation occurring in acetic acid-induced colitis. This trial showed that mesalazine alone did not incorporate the reduction of infectious events, despite its beneficial effect on inflammatory changes in experimental colitis. Metronidazole and gentamicin combination given intraperitoneally was more effective than topical mesalazine in decreasing bacterial translocation.

Bile acids enhance the activity of the insulin receptor and glycogen synthase in primary rodent hepatocytes

Previously, we demonstrated that deoxycholic acid (DCA)-induced ERK1/2 and AKT signaling in primary hepatocytes is a protective response. In the present study, we examined the regulation of the phosphatidylinositol 3 (PI3) kinase/AKT/glycogen synthase (kinase) 3 (GSK3)/glycogen synthase (GS) pathway by bile acids. In primary hepatocytes, DCA activated ERBB1 (the epidermal growth factor receptor), ERBB2, and the insulin receptor, but not the insulin-like growth factor 1 (IGF-1) receptor. DCA-induced activation of the insulin receptor correlated with enhanced phosphorylation of insulin receptor substrate 1, effects that were both blocked by the insulin receptor inhibitor AG1024 and by expression of the dominant negative IGF-1 receptor (K1003R), which inhibited in trans. Expression of the dominant negative IGF-1 receptor (K1003R) also abolished DCA-induced AKT activation. Bile acid-induced activation of AKT and phosphorylation of GSK3 were blunted by the ERBB1 inhibitor AG1478 and abolished by AG1024. Bile acids caused activation of GS to a similar level induced by insulin (50 nM); both were blocked by inhibition of insulin receptor function and the PI3 kinase/AKT/GSK3 pathway. In conclusion, these findings suggest that bile acids and insulin may cooperate to regulate glucose storage in hepatocytes.

Hepatobiliary manifestations of inflammatory bowel disease

PSC is the most common of the clinically significant hepatobiliary diseases seen in association with IBD, with an incidence that varies from 2.5% to 7.5%. Conversely, 50% to 75% of patients with PSC have IBD. This high degree of association suggests a common pathogenetic mechanism; however, no causal relationship has been established. The etiopathogenesis of PSC remains poorly understood, despite a large number of studies looking at differing hypotheses. The diagnosis is usually established by cholangiography. Liver biopsy can sometimes be helpful in diagnosing pericholangitis. There is a significant overlap of the histology with chronic hepatitis. Serum markers have been studied for diagnosing PSC, particularly for early diagnosis of cholangiocarcinoma, but none have shown the high sensitivity and specificity needed to use them clinically. PSC usually progresses insidiously and eventually leads to cirrhosis. Despite progress in early recognition, optimal management of patients with PSC remains a challenge requiring a multidisciplinary approach among hepatologists, endoscopists, surgeons, and interventional radiologists. Colectomy for ulcerative colitis does not alter the natural history of PSC. There is a high (10% to 15%) incidence of cholangiocarcinoma in patients with PSC. This incidence along with the risk of colon cancer in patients with ulcerative colitis makes it necessary to follow these patients closely. A number of pharmacologic therapies have been evaluated, but none has proven successful in slowing the progression of PSC or prolonging survival. Endoscopic therapy has a proven utility in treating complications of recurrent cholangitis or worsening jaundice in the setting of a dominant stricture, but endoscopy has not been shown to improve survival or decrease the need for liver transplantation. Liver transplantation is life-saving for patients with advanced PSC. Pericholangitis, gallstones, and chronic hepatitis are additional disorders noted in association with IBD, but they are much less common and easier to manage than PSC.

Biliary tract inflammatory disorders: primary sclerosing cholangitis and primary biliary cirrhosis

Primary sclerosing cholangitis (PSC) and primary biliary cirrhosis (PBC) are chronic progressive cholestatic diseases that frequently lead to biliary cirrhosis. The exact pathogenesis of these diseases remains elusive but is likely immunologically based. Complications range from fatigue and pruritus to end-stage liver disease. The risk of developing hepatocellular carcinoma is low for patients with PBC, whereas cholangiocarcinoma is common in PSC and carries an ominous prognosis. Although ursodeoxycholic acid is effective in slowing the progression of PBC, no effective medical therapy exists for PSC. Liver transplantation is the only option for patients with end-stage liver disease and yields excellent long-term survival in both groups.

Sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a chronic, progressive cholestatic liver disease whose aetiopathogenesis is unknown. PSC is frequently associated with inflammatory bowel disease, in particular chronic ulcerative colitis, is most commonly observed in young males and is clinically characterized by fatigue, pruritus and jaundice. The diagnosis is supported by a cholestatic biochemical profile and histological abnormalities, and confirmed by visualization of an abnormal biliary tree. The natural history of the disease is currently being evaluated but is generally recognized to be slowly progressive, leading to complications of chronic cholestasis, portal hypertension and biliary cirrhosis. There is no specific medical treatment, and orthotopic liver transplantation remains the only definitive treatment for patients with end-stage PSC. A more rational approach to medical therapy will ensue upon a better understanding of the aetiopathogenesis of this disease.

Current concepts in primary sclerosing cholangitis

OBJECTIVE

To describe primary sclerosing cholangitis (PSC) and its associated complications, as well as medical and surgical treatment.

DESIGN

A review of PSC and its associated etiopathologic factors is presented; numerous studies of agents that are used to treat patients with PSC are discussed.

RESULTS

PSC, a slowly progressive disease that often involves autoimmune damage to the biliary tree, is frequently associated with inflammatory bowel disease, usually chronic ulcerative colitis. Long-term follow-up of patients with PSC has revealed a high incidence of colon cancer and bile duct cancer, both of which are most likely related to the chronic inflammation involving these two organs. Although PSC is an unusual disease, it is now diagnosed with approximately the same frequency as is primary biliary cirrhosis. The histopathologic evolution of PSC results in irreversible damage to bile ducts, which ultimately leads to cholestasis, cirrhosis, liver failure, and premature death from liver failure unless liver transplantation is performed. Therefore, the best chance of achieving success is to treat patients with early-stage disease rather than those with irreversible end-stage cirrhotic disease. Although several medical therapies for PSC have been evaluated, only D-penicillamine, cyclosporine, methotrexate, and, most recently, ursodeoxycholic acid have been studied in controlled clinical trials. Furthermore, several surgical therapies for PSC and its associated complications have been assessed.

CONCLUSION

Currently, no therapy achieves a complete clinical, biochemical, or histologic remission in this disease. Until the etiopathogenesis of PSC is further defined, effective therapy is unlikely to be found. Thus, liver transplantation will continue to be an important therapeutic intervention for the management of patients with end-stage PSC.

Advances in primary sclerosing cholangitis

Primary sclerosing cholangitis is an increasingly recognized chronic cholestatic liver disease. It frequently occurs in association with chronic ulcerative colitis and is characterized by inflammation and fibrosis of the intrahepatic and extrahepatic bile ducts. The cause is unknown, although many mechanisms have been considered, including infectious, toxic, and immunologic. The prognosis varies. No adequate treatment exists, although a number of potential treatments have been evaluated in uncontrolled trials, and the results of controlled trials have only recently been reported. Liver transplantation has recently been shown to be an effective treatment for end-stage disease. These various advances in our understanding of primary sclerosing cholangitis are reviewed.

High concentration and retained amidation of fecal bile acids in patients with active ulcerative colitis

Fecal bile acid profiles of 14 patients with ulcerative colitis in the active phase were analyzed to study the potential significance of bile acids in the pathophysiology of this disease, and the results were compared with those in 12 healthy controls. The excretion levels of total bile acids (mean +/- SD) in patients were higher than in controls, 445.1 +/- 392.1 vs 215.5 +/- 148.0 mumol/day, 3.1 +/- 1.7 vs 1.6 +/- 1.0 mumol/g wet feces (P less than 0.05), and 17.2 +/- 9.2 vs 12.4 +/- 13.3 mumol/g dry feces. Fecal profiles of individual bile acids showed higher levels of primary bile acids (52 +/- 27%) in patients compared to those (26 +/- 21%) in controls. Proportions of glycine and taurine conjugates in patients (26 +/- 24%) were higher than in controls (5 +/- 2%) (P less than 0.05), whereas proportions of unconjugates and sulfates were lower in patients than in controls. Accordingly the extent of deconjugation and dehydroxylation of bile acids was lower in patients than in controls. These trends were prominent in patients with more severe disease activity. A high concentration of bile acids in the intestine may have a significant role in the pathophysiology of ulcerative colitis at active phase.

Bile acid-induced liver toxicity: relation to the hydrophobic-hydrophilic balance of bile acids

Hypertransaminasemia is a frequent side effect during chenodeoxycholic administration for gallstone dissolution. Evidence suggests that this effect is not mediated by lithocholic acid, the intestinal metabolite of chenodeoxycholic acid, but that toxicity is due to the chenodeoxycholic acid itself. In vitro cytotoxicity of bile salts is positively proportional to their detergent effect, which is, on the other hand, related to their hydrophobic-hydrophilic balance. We hypothesize that in vivo also liver injury can occur when the liver is perfused by an high proportion of strongly detergent bile salts. The more detergent bile salts are unconjugated or glycine conjugated, while the lesser are taurine conjugated and sulfated. Within each class the following order of decreasing detergent power can be indicated: lithocholic greater than deoxycholic greater than chenodeoxycholic greater than cholic greater than ursodeoxycholic acid. Besides chronic exogenous administration of chenodeoxycholic or deoxycholic acids, conditions in which the liver is perfused by an high mass of highly detergent bile salts are those characterized by an enhanced intestinal biodegradation of bile salts. These conditions, which are common features of some chronic inflammatory bowel diseases, are frequently associated with liver damage. On the other hand, a normally detergent bile salt pool can become hepatotoxic for liver cells which have already been injured. In this respect, as already reported for increased sulfation, the increased proportion of taurine conjugates and the reduced formation of deoxycholic acid in liver cirrhosis can be regarded as protective mechanisms. Liver toxicity induced by bile salts' detergent action can be prevented by favouring tauroconjugation or reducing the intestinal degradation of bile salts or by administering poorly detergent bile salts.

Primary sclerosing cholangitis--an immunologically mediated disease?

Primary sclerosing cholangitis (PSC) is an uncommon, chronic disorder characterized by inflammatory fibrosis usually involving the entire biliary tree. The etiology has been unknown, but PSC is closely associated with ulcerative colitis, which coexists in more than two thirds of patients with PSC. In recent studies 3% to 5% of all patients with ulcerative colitis had PSC. We propose that PSC is, at least in part, an immunologically mediated disease; it is closely associated with human leckocyte antigens B8 and DR3, and circulating autoantibodies to colon and portal tract are frequently present. The anticolon antibody cross-reacts with enteric Escherichia coli. The disease may possibly be triggered in susceptible patients with ulcerative colitis by immunization with antigens shared between enteric microorganisms and the biliary system.

Pruritus in cholestasis: no direct causative role for bile acid retention

Discrepancies have existed regarding the correlation between raised bile acid levels in cholestasis and the presence of pruritus. Nevertheless, the prevalent view is that bile acids have a direct etiologic role. To resolve the issue, we quantified separately all naturally-occurring bile acid species detectable in serum and skin, and on the skin surface of 13 patients with pruritus associated with cholestasis, 10 patients with cholestasis who did not have pruritus, three patients with uremia and generalized pruritus and in 10 controls. We were unable to find any correlations between the presence of pruritus and bile acid levels from the various sources. We did find great overlap in these same values with data from the group with cholestasis but without pruritus. As expected, the symptomatic (uremic) and asymptomatic control groups showed comparable levels. The results of the present study together with those of a similar recent study provide strong evidence against the hypothesis of a direct causative role for retained bile acids in pruritus associated with cholestasis.