Molecular aspects of bile formation and cholestasis

doi:10.1016/j.molmed.2003.10.002

Trends in Molecular Medicine

Volume 9, Issue 12, December 2003, Pages 558-564

https://doi.org/10.1016/j.molmed.2003.10.002 Get rights and content

Abstract

Recent insights into the cellular and molecular mechanisms that control the function and regulation of hepatobiliary transport have led to a greater understanding of the physiological significance of bile secretion. Individual carriers for bile acids and other organic anions in both liver and intestine have now been cloned from several species. In addition, complex networks of signals that regulate key enzymes and membrane transporters located in cells that participate in the metabolism or transport of biliary constituents are being unraveled. This knowledge has major implications for the pathogenesis of cholestatic liver diseases. Here, we review recent information on molecular aspects of hepatobiliary secretory function and its regulation in cholestasis. Potential implications of this knowledge for the design of new therapies of cholestatic disorders are also discussed.

Section snippets

Basic concepts of bile formation

Bile formation results from the active secretion of osmotically active compounds by hepatocytes into the canalicular space, followed by the passive movement of water through the tight junctions. Bile salts are the main solutes in bile and are considered to be the major osmotic driving force in the generation of bile flow, although BS-independent processes also contribute to bile production 1, 8. Transport of biliary constituents from blood to bile is a vectorial process that includes uptake

Molecular basis of hepatobiliary transport

The main membrane transporters that primarily determine hepatic bile production are now largely characterized at the molecular level. Most of them have been cloned from both human and rodent tissues. Information on the localization, nomenclature and function of hepatobiliary transporters is listed in Table 1. Some of these transporters are also expressed in tissues other than the liver, where they play specific physiological roles. Owing to space limitations, only the basic concepts of hepatic

Molecular mechanisms in cholestasis

Cholestasis is defined as the impairment of normal bile flow resulting either from a functional defect at the level of the hepatocyte or from obstruction at the bile duct level. Cholestasis can result from infections, the use of certain drugs, and autoimmune, metabolic or genetic disorders [21]. Identification of the transport proteins involved in bile formation led to the concept that altered expression and/or function of membrane transporters might underlie some forms of cholestasis.

Therapeutic perspectives

Treatment options for cholestatic diseases are limited [54]. Stimulation of defective transporter expression and function might be of therapeutic benefit in cholestasis. Treatment strategies could also be directed to support and stimulate rescue pathways such as alternative detoxification and elimination routes.

The anti-cholestatic drug ursodeoxycholic acid (UDCA) acts, at least in part, by stimulation of transporter expression or function [55]. UDCA stimulates vesicular exocytosis and

Concluding remarks

Recent insights into the mechanisms of bile formation have established that this function of the liver depends of a concerted action of membrane transporters. Molecular regulation of these hepatobiliary transport systems in cholestasis seems to be part of an adaptive response aiming to minimize the extent of cholestatic injury. A better understanding of the molecular mechanisms involved in cholestasis, particularly the role of NHRs in transcriptional regulation of hepatic transporter

Acknowledgements

This work was supported by grants from the Fondo Nacional de Ciencia y Tecnologı́a (FONDECYT Grant No. 1020641 to M.A.), the Jubilee Funds of the Austrian National Bank (Grant No. 10266 to M.T.), and the Austrian Science Foundation (Grant No. P15502 to M.T.). We apologize to the authors of numerous primary references whose work could not be cited owing to space limitations.

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Recent studies reported that the hepatic expression of AQP8 and AQP9 was downregulated in bile duct-ligated (BDL) rats and that overexpression of human AQP1 in the rat liver attenuated cholestasis. However, the hepatic expression of AQP10 and its regulatory mechanism in human cholestasis remain unclear.
Serum and liver samples were collected from 34 patients with obstructive cholestasis and from 12 control patients. Eight-week-old male C57BL/6J mice were intravenously injected with an adeno-associated virus 8 (AAV8) encoding human AQP10 driven by a hepatocyte-specific Alb promotor (AAV8-Alb promotor-hAQP10) for functional studies. Constructs of the AQP10 promoter and PLC/PRF/5-ASBT cell lines were used for regulatory mechanism studies.
AQP10 was significantly downregulated in patients with obstructive cholestasis and negatively associated with the serum levels of total bile acid (TBA). The hepatocyte-specific overexpression of hAQP10 significantly attenuated the cholestatic liver injury and intrahepatic bile acids (BA) accumulation in BDL mice. Conjugated BAs, such as TCA and inflammatory factor TNFα, significantly repressed AQP10 expression. Furthermore, NFκB p65/p50 directly bound to the AQP10 promotor and decreased its activity in PLC/RPF/5-ASBT cells and in the livers of patients with obstructive cholestasis. However, these changes were diminished by BAY 11-7082 (a specific inhibitor of NFκB signaling).
We are the first to report that AQP10 was significantly decreased in patients with obstructive cholestasis. AQP10 overexpression significantly attenuated cholestatic liver injury in BDL mice. Therefore, overexpression of hAQP10 in the liver may be a valuable strategy for cholestasis intervention.
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This work is to explore the hepatotoxicity mechanisms of PM-D by integrating network toxicology and spatially resolved metabolomics strategy.
A hepatotoxicity interaction network of PM-D was constructed based on toxicity target prediction for eight key toxic ingredients and a hepatotoxicity target collection. Then the key signaling pathways were enriched, and molecular docking verification was implemented to evaluate the ability of toxic ingredients to bind to the core targets. The pathological changes of liver tissues and serum biochemical assays of mice were used to evaluate the liver injury effect of mice with oral administration of PM-D. Furthermore, spatially resolved metabolomics was used to visualize significant differences in metabolic profiles in mice after drug administration, to screen hepatotoxicity-related biomarkers and analyze metabolic pathways.
The contents of four key toxic compounds in PM-D were detected. Network toxicology identified 30 potential targets of liver toxicity of PM-D. GO and KEGG enrichment analyses indicated that the hepatotoxicity of PM-D involved multiple biological activities, including cellular response to endogenous stimulus, organonitrogen compound metabolic process, regulation of the apoptotic process, regulation of kinase, regulation of reactive oxygen species metabolic process and signaling pathways including PI3K-Akt, AMPK, MAPK, mTOR, Ras and HIF-1. The molecular docking confirmed the high binding activity of 8 key toxic ingredients with 10 core targets, including mTOR, PIK3CA, AKT1, and EGFR. The high distribution of metabolites of PM-D in the liver of administrated mice was recognized by mass spectrometry imaging. Spatially resolved metabolomics results revealed significant changes in metabolic profiles after PM-D administration, and metabolites such as taurine, taurocholic acid, adenosine, and acyl-carnitines were associated with PM-D-induced liver injury. Enrichment analyses of metabolic pathways revealed tht linolenic acid and linoleic acid metabolism, carnitine synthesis, oxidation of branched-chain fatty acids, and six other metabolic pathways were significantly changed. Comprehensive analysis revealed that the hepatotoxicity caused by PM-D was closely related to cholestasis, mitochondrial damage, oxidative stress and energy metabolism, and lipid metabolism disorders.
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TJ treatment with fresh RS exhibited good therapeutic effect on ANIT-induced intrahepatic cholestasis in rats, which may be due to the attenuated oxidative stress in the liver tissue. It is rational for the ancients to choose fresh RS as TJ herbal patches because of its abundant protoanemonin with the character of irritant. The qualitative and quantitative results of GC-MS analysis provided the chemical basis of TJ therapy with fresh RS, which can be regarded as a simple and efficient method for the treatment of cholestasis hepatitis.
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Trends in Molecular Medicine

Molecular aspects of bile formation and cholestasis

Abstract

Section snippets

Basic concepts of bile formation

Molecular basis of hepatobiliary transport

Molecular mechanisms in cholestasis

Therapeutic perspectives

Concluding remarks

Acknowledgements

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