Bile acids in the assessment of hepatocellular function

Bile acid-microbiota crosstalk in hepatitis B virus infection

Hepatitis B virus (HBV) is a hepatotropic non-cytopathic virus characterized by liver-specific gene expression. HBV infection highjacks bile acid metabolism, notably impairing bile acid uptake via sodium taurocholate cotransporting polypeptide (NTCP), which is a functional receptor for HBV entry. Concurrently, HBV infection induces changes in bile acid synthesis and the size of the bile acid pool. Conversely, bile acid facilitates HBV replication and expression through the signaling molecule farnesoid X receptor (FXR), a nuclear receptor activated by bile acid. However, in HepaRG cells and primary hepatocytes, FXR agonists suppress HBV RNA expression and the synthesis and secretion of DNA. In the gut, the size and composition of the bile acid pool significantly influence the gut microbiota. In turn, the gut microbiota impacts bile acid metabolism and innate immunity, potentially promoting HBV clearance. Thus, the bile acid-gut microbiota axis represents a complex and evolving relationship in the context of HBV infection. This review explores the interplay between bile acid and gut microbiota in HBV infection and discusses the development of HBV entry inhibitors targeting NTCP.

Research progress of bile biomarkers and their immunoregulatory role in biliary tract cancers

Biliary tract cancers (BTCs), including cholangiocarcinoma and gallbladder carcinoma, originate from the biliary epithelium and have a poor prognosis. Surgery is the only choice for cure in the early stage of disease. However, most patients are diagnosed in the advanced stage and lose the chance for surgery. Early diagnosis could significantly improve the prognosis of patients. Bile has complex components and is in direct contact with biliary tract tumors. Bile components are closely related to the occurrence and development of biliary tract tumors and may be applied as biomarkers for BTCs. Meanwhile, arising evidence has confirmed the immunoregulatory role of bile components. In this review, we aim to summarize and discuss the relationship between bile components and biliary tract cancers and their ability as biomarkers for BTCs, highlighting the role of bile components in regulating immune response, and their promising application prospects.

Modulation of Disordered Bile Acid Homeostasis and Hepatic Tight Junctions Using Salidroside against Hepatocyte Apoptosis in Furan-Induced Mice

Furan, a processing-induced food contaminant, has attracted great attention due to its hepatotoxicity. To further investigate the underlying mechanism of salidroside (SAL) alleviating furan-induced liver damage, we divided Balb/c mice into the control group, the furan (8 mg/kg/day) group, and three groups of three different doses of SAL (10/20/40 mg/kg/day) in the current research. The shifted serum profile was observed through untargeted metabonomics, to which the bile acid metabolism was related, and the alleviating effect of SAL against furan-induced apoptosis was caused by the metabolism. Target bile acid quantification for the liver and serum showed that SAL positively regulated the homeostasis of bile acids disturbed by furan. Meanwhile, SAL significantly upregulated the synthesis genes of bile acids (Cyp7a1, Cyp7b1, Cyp8b1, and Cyp27a1) and the uptake transport genes (Ntcp and Oatps) and downregulated the efflux transport genes (Bsep, Ost-α, Ost-β, Mrp2, and Mrp4). Transmission electron microscopy of the bile canaliculi and tight junctions and the levels of tight junction marker proteins (ZO-1, occludin, and claudin-1) confirmed that the disruption of the hepatic tight junction was inhibited by SAL. The connection between the apoptosis- and tight junction-related proteins was observed through the construction of a protein-protein interaction network. SAL suppressed the furan-induced hepatocyte apoptosis evidenced by the detection of TUNEL and Bax, Bcl-2, and caspase-3 levels. Taken together, SAL alleviated furan-induced hepatocyte apoptosis via altering the disordered homeostasis of bile acids and hepatic tight junctions.

Systemic PFOS and PFOA exposure and disturbed lipid homeostasis in humans: what do we know and what not?

Associations between per- and polyfluoroalkyl substances (PFASs) and increased blood lipids have been repeatedly observed in humans, but a causal relation has been debated. Rodent studies show reverse effects, i.e. decreased blood cholesterol and triglycerides, occurring however at PFAS serum levels at least 100-fold higher than those in humans. This paper aims to present the main issues regarding the modulation of lipid homeostasis by the two most common PFASs, PFOS and PFOA, with emphasis on the underlying mechanisms relevant for humans. Overall, the apparent contrast between human and animal data may be an artifact of dose, with different molecular pathways coming into play upon exposure to PFASs at very low versus high levels. Altogether, the interpretation of existing rodent data on PFOS/PFOA-induced lipid perturbations with respect to the human situation is complex. From a mechanistic perspective, research on human liver cells shows that PFOS/PFOA activate the PPARα pathway, whereas studies on the involvement of other nuclear receptors, like PXR, are less conclusive. Other data indicate that suppression of the nuclear receptor HNF4α signaling pathway, as well as perturbations of bile acid metabolism and transport might be important cellular events that require further investigation. Future studies with human-relevant test systems would help to obtain more insight into the mechanistic pathways pertinent for humans. These studies shall be designed with a careful consideration of appropriate dosing and toxicokinetics, so as to enable biologically plausible quantitative extrapolations. Such research will increase the understanding of possible perturbed lipid homeostasis related to PFOS/ PFOA exposure and the potential implications for human health.

Toxicology and carcinogenesis studies of perfluorooctanoic acid administered in feed to Sprague Dawley (Hsd:Sprague Dawley SD) rats (revised)

Perfluorooctanoic acid (PFOA) is a perfluorinated alkyl substance (PFAS) with widespread exposure in the environment and human population. Lifetime exposure to this chemical is likely, which includes in utero and postnatal development. Previously conducted chronic carcinogenicity studies of PFOA began exposure after these critical periods of development, so it is unknown whether the carcinogenic response is altered if exposure during gestation and lactation is included. The current PFOA chronic studies were designed to assess the contribution of combined gestational and lactational exposure (herein referred to as perinatal exposure) to the chronic toxicity and carcinogenicity of PFOA. The hypothesis tested was that including exposure during gestation and lactation (perinatal exposure) with postweaning exposure would change the PFOA carcinogenic response quantitatively (more neoplasms) or qualitatively (different neoplasm types) compared to postweaning exposure alone. (Abstract Abridged).

Bile acid analysis in biliary tract cancer

The etiology of biliary tract cancer is obscure, but there are evidences that bile acid plays a role in carcinogenesis. To find the association between biliary tract cancer and bile acid, this study compared the bile acid concentration and composition among patients with biliary cancer, biliary tract stones, and no biliary disease. Bile was compared among patients with biliary tract cancer (n = 26), biliary tract stones (n = 29), and disease free controls (n = 9). Samples were obtained by percutaneous transhepatic biliary drainage, endoscopic nasobiliary drainage, or gallbladder puncture, and analyzed for cholic, deoxycholic, chenodeoxycholic, lithocholic, and ursodeoxycholic acid composition. Total bile acid concentration was lower in the cancer group than the biliary stone and control groups; the proportions of deoxycholic (2.2% vs. 10.2% and 23.6%, p < 0.001 and p < 0.001, respectively) and lithocholic acid (0.3% vs. 0.6% and 1.0%, p = 0.065 and p < 0.001, respectively) were also lower. This result was similar when disease site was limited to bile duct or gallbladder. Analysis of cases with bilirubin <or= 2.0 mg/dL also showed lower total bile acid concentration and deoxycholic acid composition in the cancer group compared to controls (5.7% vs. 23.6%, p = 0.003). Although the presence of bile duct obstruction explains some of the difference in total concentration and composition of bile acid, there are other contributing mechanisms. We suspect the alteration of bile acid transport might decrease bile acid excretion and cause the accumulation of carcinogenic bile acid in bile duct epithelium.

Influence of Verapamil and Cyclosporin A on bile acid metabolism and transport in rat liver slices

Verapamil (V) is a specific inhibitor of the P-glycoprotein (mdr1) in the hepatocyte canalicular membrane. Cyclosporin A (CsA) as an essential immunosuppressive drug has potentially cholestatic adverse effects on the liver, but increases the expression of mdr1. In precision-cut liver slices from 34- to 40-day-old male Wistar rats 26 individual free and conjugated bile acids (BAs) as markers of hepatic transport and synthesis function were analysed after 4 h incubation with V (100 microM) or CsA (5 microM) in Krebs-Henseleit buffer. Some slices were loaded with cholic acid (CA 5 microM) or tauro-ursodeoxycholic acid (T-UDCA 5 microM) to investigate the V and CsA effects under conditions of BA supplementation. BAs were determined in tissue and medium by HPLC with postcolumn derivatisation and fluorescence detection. V and CsA, influencing different targets in BA transport, enhanced slice concentrations of T- and glyco- (G-) conjugated CA only when exogenous CA was given additionally. This BA accumulation in tissue is more reflected at decreased medium concentrations of these BAs after V and CsA incubations. Both V and CsA also inhibited CA uptake into the slices. The acidic chenodeoxycholic acid (CDCA) synthesis pathway is disturbed: T- and G-CDCA concentrations are diminished in slices and medium after V and CsA incubations. T-UDCA plus V or CsA enhanced not only its own slice concentration but also the concentration of the trihydroxylated tauro-muricholic acid (T-beta-MCA), reflecting the conversion of the accumulated dihydroxylated T-UDCA into the T-beta-MCA. The similar effects of V and CsA on BA transport and metabolism can be explained by mdr1 mediated disturbances of cellular ATP transport rather than by inhibition of individual BA transporters.

Reversibility of caspase activation and its role during glycochenodeoxycholate-induced hepatocyte apoptosis

The accumulation of glycochenodeoxycholate (GCDC) induced hepatocyte apoptosis in cholestasis. However, many hepatocytes still survived GCDC-induced apoptosis. The molecular mechanism for the survival of hepatocytes remains unclear. In the present study, isolated rat hepatocytes were cultured in William's E medium and treated with 50 microM GCDC. DNA, RNA, cell lysate, and nuclear proteins were collected at different intervals for DNA fragmentation assay, reverse transcription PCR, Western blotting, and gel mobility shift assay, respectively. GCDC-induced active caspases were detected as early as 2 h by Western blotting and kinetic caspase assay, whereas hepatocyte apoptosis was found at 4 h by DNA fragmentation and terminal deoxynucleotidyl transferase-mediated dUPT nick-end labeling assay. When GCDC was removed, the increased caspases as well as NF-kappaB could be restored to control level. A1/Bfl-1 and inducible nitric oxide synthase (iNOS) were up-regulated in 2 h of GCDC stimulation. After GCDC was removed, hepatocytes decreased expression of A1/Bfl-1, but not iNOS, to the control level. NF-kappaB activation coincided with the change of A1/Bfl-1. Survivin, cIAP1, cIAP2, XIAP, and A1/Bfl-1, but not iNOS, were down-regulated by pan-caspase inhibitor benzyloxycarbonyl-VAD-fluoromethyl ketone. In addition, benzyloxycarbonyl-VAD-fluoromethyl ketone inhibited release of cytochrome c and suppressed NF-kappaB activation. Our data suggested that caspase pathway is an important regulatory factor during hepatocyte apoptosis. GCDC-induced caspase response is reversible, which may activate anti-apoptotic genes to protect hepatocytes from apoptosis.

Regulation of hepatobiliary excretion of sinomenine by P-glycoprotein in Sprague-Dawley rats

Sinomenine, an herbal ingredient isolated from Sinomenium acutum, is used for the amelioration of arthritis. Using microdialysis and a specially constructed hepato-duodenal shunt probe, the present study investigated the pharmacokinetics of sinomenine in rat blood and bile and the effects of P-glycoprotein modulation and cytochrome P450 inhibition. The results indicated that the pharmacokinetics of sinomenine in rat blood appeared to be dose dependent in the 3 to 30 mg/kg range. The disposition of sinomenine in the bile exhibited a slow elimination phase, reaching a peak concentration in 20-40 min following intravenous administration. The area under the concentration versus time curves (AUC's) for sinomenine in the bile were significantly greater than those in the blood at dosages of 3, 10, and 30 mg/kg with the blood-to-bile distribution ratios (k = AUC(bile) / AUC(blood)) being 3.85 +/- 0.29 and 3.52 +/- 0.28 at 10 and 30 mg/kg, respectively, indicating active hepatobiliary excretion. Coadministration with 20 mg/kg of cyclosporin A 10 min prior to sinomenine administration resulted in a significant reduction of the bile AUC's for the dosages of 10 and 30 mg/kg., resulting in the bile/blood distribution ratio being significantly reduced to 0.47 +/- 0.05 and 0.49 +/- 0.05, respectively. On the other hand, proadifen treatment increased both the blood and bile AUC's, resulting in insignificant effects on the blood-to-bile distribution ratios. In conclusion, our results indicated that sinomenine underwent active hepatobiliary elimination which may be regulated by the P-glycoprotein and that P-450 was likely involved in its metabolism.

Cytotoxicity of bile in human Hep G2 cells and in primary cultures of rat hepatocytes

There has been increasing interest in the development of a hepatocyte bioreactor for the treatment of acute hepatic failure; however, little is known about the effect of hepatocyte byproducts on the viability of the cells in the bioreactor environment. We investigated the effects of increasing concentrations of bile on the growth and viability of the human hepatoma cell line Hep G2 and on the cytochrome P-450 content and dependent mixed function oxidase (MFO) activities, reduced glutathione (GSH) content, and glutathione S-transferase (GST) activity of primary cultures of rat hepatocytes. Our purpose was to determine whether or not it would be necessary to pretreat the plasma from patients with acute liver failure to remove elevated bile concentrations which might be toxic to the hepatocytes in an artificial liver device. Bile was found to inhibit Hep G2 cell growth at concentrations as low as 0.1% and to decrease viability at concentrations above 0.5%. The cytochrome P-450 and GSH contents and the activities of the MFO system and of GST were decreased in the primary cultures of hepatocytes following 24 h treatment with concentrations of bile at and above 0.5%. The MFO activities associated with different cytochrome P-450 isoenzymes decreased to different extents in the presence of bile with the O-dealkylation of pentoxyresorufin being more labile than that of ethoxyresorufin. Our data indicate that elevated bile concentrations are cytotoxic to liver cells, and it may be necessary to pretreat patient plasma to decrease its bile content to protect the cells during the clinical operation of a hepatocyte bioreactor device.