Gastroenterology

Gastroenterology

Volume 152, Issue 5, April 2017, Pages 1126-1138.e6
Gastroenterology

Original Research
Full Report: Basic and Translational—Alimentary Tract
Intestinal Farnesoid X Receptor Controls Transintestinal Cholesterol Excretion in Mice

https://doi.org/10.1053/j.gastro.2016.12.037Get rights and content

Background & Aims

The role of the intestine in the maintenance of cholesterol homeostasis increasingly is recognized. Fecal excretion of cholesterol is the last step in the atheroprotective reverse cholesterol transport pathway, to which biliary and transintestinal cholesterol excretion (TICE) contribute. The mechanisms controlling the flux of cholesterol through the TICE pathway, however, are poorly understood. We aimed to identify mechanisms that regulate and stimulate TICE.

Methods

We performed studies with C57Bl/6J mice, as well as with mice with intestine-specific knockout of the farnesoid X receptor (FXR), mice that express an FXR transgene specifically in the intestine, and ABCG8-knockout mice. Mice were fed a control diet or a diet supplemented with the FXR agonist PX20606, with or without the cholesterol absorption inhibitor ezetimibe. Some mice with intestine-specific knockout of FXR were given daily injections of fibroblast growth factor (FGF)19. To determine fractional cholesterol absorption, mice were given intravenous injections of cholesterol D5 and oral cholesterol D7. Mice were given 13C-acetate in drinking water for measurement of cholesterol synthesis. Bile cannulations were performed and biliary cholesterol secretion rates were assessed. In a separate set of experiments, bile ducts of male Wistar rats were exteriorized, allowing replacement of endogenous bile by a model bile.

Results

In mice, we found TICE to be regulated by intestinal FXR via induction of its target gene Fgf15 (FGF19 in rats and human beings). Stimulation of this pathway caused mice to excrete up to 60% of their total cholesterol content each day. PX20606 and FGF19 each increased the ratio of muricholate:cholate in bile, inducing a more hydrophilic bile salt pool. The altered bile salt pool stimulated robust secretion of cholesterol into the intestinal lumen via the sterol-exporting heterodimer adenosine triphosphate binding cassette subfamily G member 5/8 (ABCG5/G8). Of note, the increase in TICE induced by PX20606 was independent of changes in cholesterol absorption.

Conclusions

Hydrophilicity of the bile salt pool, controlled by FXR and FGF15/19, is an important determinant of cholesterol removal via TICE. Strategies that alter bile salt pool composition might be developed for the prevention of cardiovascular disease. Transcript profiling: http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?token=irsrayeohfcntqx&acc=GSE74101.

Section snippets

Animal Experiments

Male age-matched, wild-type (WT) C57Bl/6J mice, intestine-specific FXR knock-out (iFXR KO; generated by crossing mice expressing Cre-recombinase under the control of the villin18 promoter with Fxr-floxed mice19; kindly provided by Dr Frank J. Gonzalez), intestine-specific FXR-transgenic mice (iFXR TG; see the Supplementary Materials and Methods section) and their nontransgenic littermates (FXR KO),20 as well as ABCG8 knock-out (ABCG8 KO) mice and their WT littermates21 were housed in a light

Pharmacologic Activation of FXR Markedly Enhances Fecal Neutral Sterol Excretion in Mice

To delineate the role of bile salts in control of body cholesterol fluxes, we chose to modify bile salt synthesis and pool composition via modulation of the activity of the bile salt–activated nuclear receptor FXR. C57BL/6J mice were treated with the FXR agonist PX20606 for 2 weeks. In line with data obtained in hyperlipidemic mice and monkeys,23 the compound was well tolerated and had no effect on body weight or food intake (data not shown). PX treatment decreased plasma cholesterol and

Discussion

In this study we show that the intestine itself has the capability to facilitate elimination of enormous amounts of cholesterol from the body via the TICE pathway. The large capacity of TICE that became evident from the current studies highlights the potential of the intestine as a target for future cholesterol-lowering therapies. The induction of TICE in response to FXR activation appears to be mediated by hydrophilic bile salts. The fact that the magnitude of induction of FNS excretion and

Acknowledgments

The authors are grateful to Dr Frank J. Gonzalez (National Cancer Institute, National Institutes of Health, Bethesda, MD) for providing the Fxr-floxed mice.

References (42)

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Conflicts of interest This author discloses the following: Claus Kremoser is the CEO of Phenex Pharmaceuticals AG, Heidelberg, Germany. The remaining authors disclose no conflicts.

Funding Supported within the framework of Top Institute Pharma, The Netherlands, project T2-110, and in part by European Union grant FP7-HEALTH 305707.

Author names in bold designate shared co-first authorship

Authors share co-first authorship.

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