Neutraceutical Targeting of the Bile Acid Receptor, Farnesoid X Receptor, for Intestinal Disease
Authors: Fallon Ciara M. , Edupuganti Omprakash , Lajczak-McGinley Natalia K. , Sheridan Helen , Keely Stephen J. 
Published: April 2020

INTRODUCTION

Bile acids, classically known for their roles in fat digestion, are now recognised as important regulators of many aspects of intestinal physiology, including epithelial proliferation/apoptosis, transport and barrier function. Thus, the nuclear bile acid receptor, farnesoid X receptor (FXR), represents a promising therapeutic target for intestinal disorders, such as inflammatory bowel disease and colorectal cancer. Previous studies suggest dietary plant‐derived phytochemicals may modulate FXR activity.

AIMS

To investigate the effects of a phytochemical, denoted KFS1, and a KFS1 rich plant extract, denoted as QE1, on FXR signalling in colonic epithelial cells.

METHODS

T84 colonic epithelial cells, grown as polarised monolayers, were treated bilaterally with the FXR agonist, GW4064 (5 μM), KFS1 (1 – 100 μM) or QE1 (30 – 100 μg/ml) for 24 hr. Expression of FXR and FGF‐19, an index of FXR activation, were measured by qRT‐PCR, western blotting and ELISA. Transepithelial electrical resistance (TEER) was measured as an index of epithelial barrier function. Lactate dehydrogenase (LDH) release and PARP cleavage were used as measurements of necrosis and apoptosis, respectively. FXR activity was also studied using an FXR/luciferase reporter HepG2 cell line. Data are expressed as the mean ± SEM for a series of n experiments.

RESULTS

GW4064 (5 μM) induced a 719.8 ± 183.3 fold increase in FGF‐19 mRNA expression (n = 20; p<0.001) and a 10.4 ± 4.9 fold increase in FGF‐19 protein release (n = 5; p<0.01). KFS1 (5 – 100 μM) did not alter FGF‐19 protein expression and at higher concentrations (50 – 100 μM) reduced TEER. Similarly, GW4064 (5 μM) significantly induced luciferase activity in FXR HepG2 reporter cells by 1580.7 ± 195.7 counts per second (p<0.001; n = 3), whereas treatment with KFS1 (1 – 100 μM) was without effect. Lower concentrations of KFS1 (5 μM), which alone did not alter TEER, increased FXR mRNA and protein expression by 4.2 ± 0.4 (p<0.05; n = 4) and 1.5 ± 0.04 fold (p<0.05; n = 4), respectively. Moreover, pre‐treatment of T84 cells with KFS1 (1, 5, or 10 μM) for 1 hr prior to treatment with GW4064 (5 μM; 24 hr) potentiated GW4064‐induced FGF‐19 mRNA expression by 2.5 ± 0.8, 2.9 ± 0.2, and 4.6 ± 0.5 fold, respectively (p<0.05; n = 6) and FGF‐19 protein expression by 2.5 ± 0.4, 4.1 ± 0.5, and 4.6 ± 0.5 fold, respectively (p<0.05, p<0.001; n = 7). Combined treatment with KFS1 (1, 5, 10 μM) and GW4064 (5 μM) also significantly reduced TEER to 49.8 ± 7.4%, 50.6 ± 8.3%, and 40.6 ± 6.6% of control values, respectively (n = 7). TEER reductions in response to such co‐treatments were not associated with significant LDH release or PARP cleavage (n = 3). Finally, a methanolic extract of plant material known to be rich in KFS1, QE1 (100 μg/ml), increased GW4064‐induced FGF‐19 release in T84 cells by 2.1 ± 0.3 fold (n = 6; p<0.01).

CONCLUSION

These data demonstrate that KFS1, a common dietary phytochemical, induces FXR expression in colonic epithelial cells and prime the cells for agonist‐induced FXR activation. These findings suggest that foods, or food supplements, rich in such plant‐derived phytochemicals have potential for development as FXR‐targeted neutraceuticals.

Support or Funding Information

StAR PhD Scholarship from RCSI & Science Foundation Ireland (SFI)