Attenuated Accumulation of Novel Fluorine (¹⁹F)-Labeled Bile Acid Analogues in Gallbladders of Fibroblast Growth Factor-15 (FGF15)-Deficient Mice

Abstract

Our work has focused on defining the utility of fluorine (19F)-labeled bile acid analogues and magnetic resonance imaging (MRI) to identify altered bile acid transport in vivo. In the current study, we explored the ability of this approach to differentiate fibroblast growth factor-15 (FGF15)- deficient from wild-type (WT) mice, a potential diagnostic test for bile acid diarrhea, a commonly misdiagnosed disorder. FGF15 is the murine homologue of human FGF19, an intestinal hormone whose deficiency is an underappreciated cause of bile acid diarrhea. In a pilot and three subsequent pharmacokinetic studies, we treated mice with two 19F-labeled bile acid analogues, CA-lys-TFA and CA-sar-TFMA. After oral dosing, we quantified 9F-labeled bile acid analogue levels in the gallbladder, liver, small and large intestine, and plasma using liquid chromatography mass spectrometry (LC-MS/MS). Both 19F bile acid analogues concentrated in the gallbladders of FGF15-deficient and WT mice, attaining peak concentrations at approximately 8.5 h after oral dosing. However, analogue levels in gallbladders of FGF15-deficient mice were several-fold less compared to those in WT mice. Live-animal 19F MRI provided agreement with our LC-MS/MS-based measures; we detected robust CA-lys-TFA 19F signals in gallbladders of WT mice but no signals in FGF15-deficient mice. Our finding that 19F MRI differentiates FGF15-deficient from WT mice provides additional proof-of-concept for the development of 19F bile acid analogues and 19F MRI as a clinical test to diagnose bile acid diarrhea due to FGF19 deficiency and other disorders.

Intestinal Absorption of Bile Acids in Health and Disease

“…These methods are likely insufficient to study dynamic, posttranslational changes in ASBT activity, necessitating the development of real-time methods. Several recent approaches have been developed to quantify the aspects of bile acid physiology in -real time (76,115,263,311,389,392,(397)(398)(399). Additionally, a recent bioluminescence-based approach relying on a CA-luciferin-conjugated probe has shown promising results for measuring real-time ASBT activity in vitro and in isolated intestinal epithelial cells (377).…”

Bile acids and their role in functional gastrointestinal disorders

“…One study reported on the utility of fluorine (19F)-labeled bile acid analogs and magnetic resonance imaging (MRI) in identifying altered bile acid transport in mice. 10 Two groups of mice were compared: wild-type and FGF15-deficient mice (FGF15 is a murine homolog of human FGF-19). After dosing the animals orally, the researchers quantified 19F-labeled bile acid analog levels in the gallbladder, liver, intestine, and plasma using liquid chromatography.…”

A 19F magnetic resonance imaging-based diagnostic test for bile acid diarrhea

“…Additionally, the structural properties of CA-sar-TFMA and CA-lys-TFA permit their transport within the enterohepatic circulation since they are substrates for both ileal ASBT and the hepatic Na+/taurocholate co-transporting polypeptide (NTCP). Despite their different structures, these bile acid analogues performed alike, sufficiently to assess impaired bile acid transport within the enterohepatic circulation [ 25 ]. In our studies, incubation of CA-sar-TFMA and CA-lys-TFA with stool and gallbladder homogenates for up to 24 h revealed no significant degradation in either 19 F-bile acid analogue [ 25 ].…”

“…Despite their different structures, these bile acid analogues performed alike, sufficiently to assess impaired bile acid transport within the enterohepatic circulation [ 25 ]. In our studies, incubation of CA-sar-TFMA and CA-lys-TFA with stool and gallbladder homogenates for up to 24 h revealed no significant degradation in either 19 F-bile acid analogue [ 25 ].…”

“…CA-sar-TFMA and CA-lys-TFA concentrated in the gallbladder above the 19 F-MRI limit of detection of 2.27 mM of bile acid analogue, as there are three equivalent fluorine atoms in each structure. The 19 F-MRI limit of detection was determined to be the noise magnitude plus 2.5 times the noise standard deviation, calculated from a region of interest (ROI) near the periphery of the image [ 25 ]. Using this method, there is greater than 99% confidence that voxels containing bile acid analogue concentrations above 6.82 mM relative to the phantom are from actual 19 F signal, and not noise.…”