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  • Review Article
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Targeting bile-acid signalling for metabolic diseases

Nature Reviews Drug Discovery volume 7, pages 678–693 (2008)Cite this article

Key Points

  • Hepatic synthesis of bile acids is the primary pathway for cholesterol catabolism. The cholesterol 7α-hydroxylase enzyme (encoded by CYP7A1) represents the rate-limiting step of the multi-enzymatic bile-acid biosynthetic pathway.

  • Bile acids play a crucial role in dietary lipid digestion and absorption, and also act as versatile signalling molecules through the activation of the nuclear hormone receptor farnesoid X receptor-α (FXR-α) and the recently identified G-protein-coupled receptor TGR5.

  • Bile-acid-mediated activation of FXR-α-signalling pathways regulate the enterohepatic recycling of bile acids, protect against their accumulation in the liver and inhibit their own biosynthesis.

  • Through their endocrine function, bile acids also activate TGR5 signalling pathways in multiple cells, through which they control immune function, liver and gall-bladder physiology and glucose and energy homeostasis.

  • The development of TGR5 agonists could have benefits to combat many aspects of the metabolic syndrome, whereas FXR-α agonists could hold promise for reducing hypertriglyceridaemia and modulating glucose metabolism. Pharmaceutical activation of these bile-acid-signalling pathways is therefore a novel way to improve metabolism.

Abstract

Bile acids are increasingly being appreciated as complex metabolic integrators and signalling factors and not just as lipid solubilizers and simple regulators of bile-acid homeostasis. It is therefore not surprising that a number of bile-acid-activated signalling pathways have become attractive therapeutic targets for metabolic disorders. Here, we review how the signalling functions of bile acids can be exploited in the development of drugs for obesity, type 2 diabetes, hypertriglyceridaemia and atherosclerosis, as well as other associated chronic diseases such as non-alcoholic steatohepatitis.

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Figure 1: Bile-acid synthesis pathways.
Figure 2: Structure and hydrophobic/hydrophilic profile of bile acids.
Figure 3: Overview of the bile-acid transport system.
Figure 4: FXR-mediated genomic actions of bile acids.
Figure 5: TGR5: a dedicated membrane bile-acid receptor.
Figure 6: A model for the TGR5 ligand binding pocket.

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Acknowledgements

The authors acknowledge support by grants from the Centre National de la Recherche Scientifique, the Institut National de la Santé et de la Recherche Médicale, the Université Louis Pasteur, the Hôpital Universitaire de Strasbourg, the National Institutes of Health (DK59820 and DK067320), L'Agence Nationale pour la Recherche (ANR 07-PHYSIO-003-01), La Fondation pour la Recherche Médicale, Ligue contre le Cancer, Intercept Pharmaceuticals (New York, USA), the Ecole Polytechnique Federale de Lausanne and the European Union (LSHM-CT-2004-512,013), and by fellowships from Société Française de Nutrition and L'Association pour la Recherche sur le Cancer (to C.T.). We apologize to those authors whose original work could not be quoted owing to space restrictions.

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Authors and Affiliations

  1. Institute of Genetics and Molecular and Cellular Biology, 1 Rue Laurent Fries, Illkirch, 67404, France

    Charles Thomas, Johan Auwerx & Kristina Schoonjans

  2. Department of Chemistry and Pharmaceutical Technology, University of Perugia, Perugia, 06123, Italy

    Roberto Pellicciari

  3. Intercept Pharmaceuticals, 18 Desbrosses Street, New York, 10013, New York, USA

    Mark Pruzanski

  4. Mouse Clinical Institute, 1 Rue Laurent Fries, Illkirch, 67404, France

    Johan Auwerx

  5. Swiss Federal Institute of Technology, Lausanne, 1015, CH, Switzerland

    Johan Auwerx & Kristina Schoonjans

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Correspondence to Johan Auwerx or Kristina Schoonjans.

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J.A. and R.P. are consultants for Intercept Pharmaceuticals, and M.P. is CEO of Intercept Pharmaceuticals, a company that is developing FXR-α and TGR5 ligands.

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Glossary

Bile canaliculus

One of the intercellular channels that occur between liver cells that form the first portion of the bile system. The different components of bile, synthesized and secreted by hepatocytes, are collected in these bile canaliculi, which merge and ultimately form bile ductules.

Atherosclerosis

A chronic inflammatory response in the walls of arteries, in large part due to the infiltration of macrophages, which accumulate cholesterol from low-density lipoproteins. Without the adequate removal of this cholesterol by high-density lipoproteins, these macrophages become foam cells.

Cerebrotendinous xanthomatosis

An inherited disorder that is associated with elevated circulating cholesterol levels and deposition of cholestanol in the brain and other tissues. This disorder is characterized by progressive cerebellar ataxia beginning after puberty, by juvenile cataracts, and by tendinous or tuberous xanthomas.

Syntenic

Describes a preserved co-localization of genes on chromosomes between different species.

Brown adipose tissue

Brown adipose tissue (BAT) is one of the two types of adipose tissue, the other being white adipose tissue. BAT is present in human newborns or small mammals. Its primary purpose is to generate body heat, owing to a high density of mitochondria.

Lithogenic diet

An experimental diet to induce cholelithiasis or cholesterol gallstones in the gall bladder.

Kupffer cells

Kupffer cells are specialized macrophages located in the liver that are part of the reticuloendothelial system.

Incretins

Incretins are gastrointestinal hormones that cause an increase in the amount of insulin released from the pancreatic β-cells after a meal. Gastric inhibitory peptide (GIP) — also known as glucose-dependent insulinotropic peptide — and glucagon-like peptide 1 (GLP1) are the two main incretins secreted by the enteroendocrine K and L cells, respectively.

Hypertriglyceridaemia

Denotes high levels of triglycerides in the blood.

Type 2 iodothyronine deiodinase

This enzyme activates thyroid hormone by converting the prohormone thyroxine (T4) by outer ring deiodination to the bioactive 3,3′,5-triiodothyronine (T3).

Diabesity

An association of obesity and type 2 diabetes.

Endoplasmic reticulum stress

Cellular disturbances causing an accumulation of unfolded proteins in the endoplasmic reticulum, which results in activation of the unfolded protein response.

Non-alcoholic steato-hepatitis

Non-alcoholic steatohepatitis (NASH) is a common and often silent liver disease, which has become one of the most prevalent alcohol-independent causes of liver cirrhosis in Western countries. Similar to non-alcoholic fatty liver disease (NAFLD), NASH is characterized by the accumulation of hepatic fat droplets, but distinguishes itself from NAFLD by the presence of a significant inflammatory component.

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Thomas, C., Pellicciari, R., Pruzanski, M. et al. Targeting bile-acid signalling for metabolic diseases. Nat Rev Drug Discov 7, 678–693 (2008). https://doi.org/10.1038/nrd2619

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