Tauroursodeoxycholic acid enhances phagocytosis of the cultured rat Kupffer cell

Dexamethasone restores transforming growth factor-β activated kinase 1 expression and phagocytosis activity of Kupffer cells in cholestatic liver injury

The role of transforming growth factor-β activated kinase 1 (TAK1) in modulating the function of Kupffer cells (KCs) within cholestatic livers remains unclear. This study examined the immunopharmacological action of dexamethasone (DEX) in modulating hepatic TAK1 expression and related signaling activity in a rat model of bile duct ligation-mimicked obstructive jaundice. The in vitro effects of DEX on porcine biliary extract (PBE)-modulated gene expression and phagocytosis of KCs were examined using a rat alveolar macrophage cell line (NR8383 cells). Although DEX therapy did not restore the downregulated TAK1 expression and phosphorylation, it significantly attenuated the upregulation of high-mobility group box 1 expression and caspase-3 activation in whole liver extracts of cholestatic rats, possibly via enhancing extracellular signal-regulated kinase-mediated signaling. Dual immunofluorescence staining of cholestatic livers and western detection on primary KCs isolated from cholestatic livers identified that DEX treatment indeed increased both the expression and phosphorylation levels of TAK1 in the KCs of cholestatic livers. In vitro studies using alveolar NR8383 macrophages with KC-characteristic gene expression further demonstrated that DEX not only repressed the pro-inflammatory cytokine production including with respect to interleukin (IL)-1β and IL-6, but also enhanced gene expression of TAK1 and a phagocytic marker, natural-resistance-associated macrophage protein 1, under PBE-mimicked cholestatic conditions. However, WST-1 assay showed that DEX did not protect NR8383 macrophages against the PBE-induced cytotoxicity. Immunofluorescence visualization of cellular F-actin by phalloidin suggested that DEX sustained the PBE-induced phagocytosis morphology of NR8383 macrophages. In conclusion, DEX treatment may pharmacologically restore the expression and activity of TAK1 in KCs, and sustain the phagocytic phenotype of KCs in cholestatic livers.

Bile acids and their receptors

Primary bile acids are synthetized from cholesterol within the liver and then transformed by the bacteria in the intestine to secondary bile acids. In addition to their involvement in digestion and fat solubilization, bile acids also act as signaling molecules. Several receptors are sensors of bile acids. Among these receptors, this review focuses on the nuclear receptor FXRα and the G-protein-coupled receptor TGR5. This review briefly presents the potential links between bile acids and cancers that are discussed in more details in the other articles of this special issue of Molecular Aspects of Medicine focused on "Bile acids, roles in integrative physiology and pathophysiology".

Conjugated bile acids in gallbladder bile and serum as potential biomarkers for cholesterol polyps and adenomatous polyps

PURPOSE

To identify conjugated bile acids in gallbladder bile and serum as possible biomarkers for cholesterol polyps (CPs) and adenomatous polyps (APs).

METHODS

Gallbladder bile samples and serum samples were collected from 18 patients with CPs (CP group), 9 patients with APs (AP group), and 20 patients with gallstones (control group) from March to November, 2013. High performance liquid chromatography (HPLC) assay with ultraviolent detection was used to detect the concentration of 8 conjugated bile acids (glycocholic acid, GCA; taurocholic acid, TCA; glycochenodeoxycholic acid, GCDCA; taurochenodeoxycholic acid, TCDCA; glycodeoxycholic acid, GDCA; taurodeoxycholic acid, TDCA; taurolithocholic acid, TLCA; tauroursodeoxycholic acid, TUDCA) in bile samples and serum samples. The diagnostic efficacy of serum GCA, GCDCA and TCDCA was evaluated.

RESULTS

These 8 conjugated bile acids in gallbladder bile and serum were completely identified within 10 minutes with good linearity (correlation coefficient: R>0.9900; linearity range: 3.91-500 µg/mL). Among these conjugated bile acids, the levels of gallbladder bile GCDCA and TCDCA in the CP group were significantly higher than those in the AP group (p<0.05). Furthermore, serum GCDCA and TCDCA as well as GCA were significantly higher in the AP group than the CP group (p<0.05). Serum GCDCA alone (≤12 µg/mL) had relatively better diagnostic efficacy than the other conjugated bile acids.

CONCLUSIONS

The levels of serum GCA, GCDCA and TCDCA may be valuable for differentiation of APs and CPs.

Bile acids PKA-dependently induce a switch of the IL-10/IL-12 ratio and reduce proinflammatory capability of human macrophages

That cholestatic conditions are accompanied by an enhanced susceptibility to bacterial infection in human and animal models is a known phenomenon. This correlates with the observation that bile acids have suppressive effects on cells of innate and adaptive immunity. The present study provides evidence that in human macrophages, bile acids inhibit the LPS-induced expression of proinflammatory cytokines without affecting the expression of the anti-inflammatory cytokine IL-10. This results in a macrophage phenotype that is characterized by an increased IL-10/IL-12 ratio. Correspondingly, bile acids suppress basal phagocytic activity of human macrophages. These effects of bile acids can be mimicked by cAMP, which is presumably induced TGR5-dependently. The data provided further suggest that in primary human macrophages, modulation of the macrophage response toward LPS by bile acids involves activation of CREB, disturbed nuclear translocation of NF-κB, and PKA-dependent enhancement of LPS-induced cFos expression. The increase in cFos expression is paralleled by an enhanced formation of a protein complex comprising cFos and the p65 subunit of NF-κB. In summary, the data provided suggest that in human macrophages, bile acids induce an anti-inflammatory phenotype characterized by an increased IL-10/IL-12 ratio via activation of PKA and thereby, prevent their activation as classically activated macrophages. This bile acid-induced modulation of macrophage function may also be responsible for the experimentally and clinically observed anti-inflammatory and immunosuppressive effects of bile acids.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

Developments in understanding bile acid metabolism

Bile acids (BAs) are not only facilitators participating in the absorption of dietary lipids and soluble vitamins, but are also important signaling molecules exerting versatile biophysiological effects. Three major signaling pathways, including the MAPK pathways, the nuclear hormone receptor farnesoid X receptor a-mediated pathways and the G protein-coupled receptor TGR5/M-BAR-mediated pathways, have been identified to be the targets of BAs. BAs, the biologically many-sided and toxic molecules, regulate the homeostasis of themselves via these signaling pathways. BAs also affect diverse metabolic status including glucose metabolism, lipid metabolism, energy expenditure, immunity and others. BAs and their related signaling mechanisms are attractive therapeutic targets of various diseases such as metabolic syndrome.

Endocrine and paracrine role of bile acids

Bile acids are not only important for the absorption of dietary lipids and fat soluble vitamins but are signalling molecules with diverse endocrine and paracrine functions. Bile acids regulate bile acid, lipid and glucose metabolism and modulate temperature and energy homeostasis. Furthermore, bile acids can not only promote cell proliferation and liver regeneration but can also induce programmed cell death. Bile acid functions are mediated through different pathways which comprise the activation of nuclear hormone receptors, of intracellular kinases and of the plasma membrane-bound, G-protein coupled bile acid receptor TGR5/Gpbar-1.

The macrophage at the crossroads of insulin resistance and atherosclerosis

The macrophage has emerged as an important player in the pathogenesis of both atherosclerosis and insulin resistance. Cross-talk between inflammatory macrophages and adipocytes may be involved in insulin resistance in peripheral tissues. Defective insulin signaling in cells of the arterial wall including macrophages may promote the development of atherosclerosis. Insulin resistant macrophages are more susceptible to endoplasmic reticulum stress and apoptosis in response to various stimuli such as nutrient deprivation, free cholesterol loading, and oxidized LDL. Increased apoptosis of insulin resistant macrophages and impaired phagocytic clearance of apoptotic cells by insulin resistant macrophages in atherosclerotic lesions may lead to enhanced postapoptotic necrosis, larger lipid-rich cores, increased inflammation, and more complex vulnerable plaques.

T cell targeting and phagocytosis of apoptotic biliary epithelial cells in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is characterized by loss of tolerance against ubiquitously expressed mitochondrial autoantigens followed by biliary and salivary gland epithelial cell (BEC and SGEC) destruction by autoreactive T cells. It is unclear why BECs and SGECs are targeted. Previous work demonstrated that the reduced form of the major PBC autoantigen predominated in apoptotic BECs and SGECs as opposed to an oxidized form in other apoptotic cells. This led to the hypothesis that presentation of novel self-peptides from phagocytosed apoptotic BECs might contribute to BEC targeting by autoreactive T cells. The effect of autoantigen redox status on self-peptide formation was examined along with the phagocytic ability of BECs. Oxidation of PBC autoantigens first was shown to be due to protein S-glutathionylation of lipoyllysine residues. Absence of protein S-glutathionylation generated novel self-peptides and affected T cell recognition of a lipoyllysine containing peptide. Liver biopsy staining revealed BEC phagocytosis of apoptotic BECs (3.74+/-2.90% of BEC) was present in PBC (7 of 7 cases) but not in normal livers (0 of 3). BECs have the ability to present novel mitochondrial self-peptides derived from phagocytosed apoptotic BECs. Apoptotic cell phagocytosis by non-professional phagocytes may influence the tissue specificity of autoimmune diseases.

Metabolic, antioxidant, nutraceutical, probiotic, and herbal therapies relating to the management of hepatobiliary disorders

Many nutraceuticals, conditionally essential nutrients, and botanical extracts have been proposed as useful in the management of liver disease. The most studied of these are addressed in terms of proposed mechanisms of action, benefits, hazards, and safe dosing recommendations allowed by current information. While this is an area of soft science, it is important to keep an open and tolerant mind, considering that many major treatment discoveries were in fact serendipitous accidents.