Bile acids (BAs) are diverse molecules that are synthesized from cholesterol in the liver. The synthesis of BAs has traditionally been shown to occur through two pathways. Cholesterol 7α‐hydroxylase (CYP7A1) performs the initial and rate‐limiting step in the classical pathway, and sterol 27‐hydroxylase (CYP27A1) initiates the hydroxylation of cholesterol in the alternative pathway. While the role of individual BA species as physiological detergents is relatively ubiquitous, their endocrine functions as signaling molecules and roles in disease pathogenesis have been emerging to be BA species–specific. In order to better understand the pharmacologic and toxicologic roles of individual BA species in an in vivo model, we created cholesterol 7α‐hydroxylase (Cyp7a1) and sterol 27‐hydroxylase (Cyp27a1) double knockout (DKO) mice by cross‐breeding single knockout mice (Cyp7a1–/– and Cyp27a1–/–). BA profiling and quantification by liquid chromatography–mass spectrometry of serum, gallbladder, liver, small intestine, and colon of wild‐type, Cyp7a1–/–, Cyp27a1–/–, and DKO mice showed that DKO mice exhibited a reduction of BAs in the plasma (45.9%), liver (60.2%), gallbladder (76.3%), small intestine (88.7%), and colon (93.6%), while maintaining a similar BA pool composition compared to wild‐type mice. The function of the farnesoid X receptor (FXR) in DKO mice was lower, revealed by decreased mRNA expression of well‐known FXR target genes, hepatic small heterodimer partner, and ileal fibroblast growth factor 15. However, response to FXR synthetic ligands was maintained in DKO mice as treatment with GW4064 resulted in similar changes in gene expression in all strains of mice. Conclusion: We provide a useful tool for studying the role of individual BAs in vivo; DKO mice have a significantly reduced BA pool, have a similar BA profile, and maintained response to FXR activation.

Farnesoid X receptor (FXR) belongs to the nuclear receptor superfamily with its endogenous ligands bile acids. Mice with whole body FXR deficiency develop liver tumors spontaneously, but the underlying mechanism is unclear. Moreover, it is unknown whether FXR deficiency in liver alone serves as a tumor initiator or promoter during liver carcinogenesis. This study aims to evaluate the effects of hepatocyte-specific FXR deficiency (FXR(hep-/-)) in liver tumor formation. The results showed that FXR(hep-/-) mice did not show spontaneous liver tumorigenesis with aging (up to 24 mo of age). Therefore FXR(hep-/-) mice were fed a bile acid (cholic acid)-containing diet alone or along with a liver tumor initiator, diethylnitrosamine (DEN). Thirty weeks later, no tumors were found in wild-type or FXR(hep-/-) mice without any treatment or with DEN only. However, with cholic acid, while only some wild-type mice developed tumors, all FXR(hep-/-) mice presented with severe liver injury and tumors. Interestingly, FXR(hep-/-) mouse livers increased basal expression of tumor suppressor p53 protein, apoptosis, and decreased basal cyclin D1 expression, which may prevent tumor development in FXR(hep-/-) mice. However, cholic acid feeding reversed these effects in FXR(hep-/-) mice, which is associated with an increased cyclin D1 and decreased cell cycle inhibitors. More in-depth analysis indicates that the increased in cell growth might result from disturbance of the MAPK and JAK/Stat3 signaling pathways. In conclusion, this study shows that hepatic FXR deficiency may only serve as a tumor initiator, and increased bile acids is required for tumor formation likely by promoting cell proliferation.

The farnesoid X receptor (Fxr) controls bile acid homeostasis by coordinately regulating the expression of synthesizing enzymes (Cyp7a1, Cyp8b1), conjugating enzymes (Bal, Baat) and transporters in the ileum (Asbt, Ostα/β) and liver (Ntcp, Bsep, Ostβ). Transcriptional regulation by Fxr can be direct, or through the ileal Fgf15/FGF19 and hepatic Shp pathways. Circulating bile acids are increased during pregnancy due to hormone-mediated disruption of Fxr signaling. While this adaptation enhances lipid absorption, elevated bile acids may predispose women to develop maternal cholestasis. The objective of this study was to determine whether short-term treatment of pregnant mice with GW4064 (a potent FXR agonist) restores Fxr signaling to the level observed in virgin mice. Plasma, liver and ilea were collected from virgin and pregnant mice administered vehicle or GW4064 by oral gavage. Treatment of pregnant mice with GW4064 induced ileal Fgf15, Shp and Ostα/β mRNAs, and restored hepatic Shp, Bal, Ntcp, and Bsep back to vehicle-treated virgin levels. Pregnant mice exhibited 2.5-fold increase in Cyp7a1 mRNA compared to virgin controls, which was reduced by GW4064. Similarly treatment of mouse primary hepatocytes with plasma isolated from pregnant mice induced Cyp7a1 mRNA by nearly 3-fold as compared to virgin plasma, which could be attenuated by co-treatment with either GW4064 or recombinant FGF19 protein. Collectively, these data reveal that repressed activity of intestinal and hepatic Fxr in pregnancy, as previously demonstrated, may be restored by pharmacological activation. This study provides the basis for a novel approach to restore bile acid homeostasis in patients with maternal cholestasis.

Vertebral artery dissection (VAD) is a cause of brain stem stroke in the younger population and is commonly associated with trauma, sudden neck movement, or chiropractic manipulations. In this case, a 28-year-old male with a non-significant past medical history who recently started a CrossFit boot camp presented to the emergency department with right-sided neck pain, dysarthria, mild right gaze paresis, right dysmetria, and right facial droop with symptoms of Horner’s syndrome. Imaging results revealed an age-indeterminate left lateral cerebellar infarct with right VAD. The goal of management is to prevent stroke, which is done with anticoagulation and potentially thrombolytic therapy if there are no contraindications. The patient received thrombolytic therapy and was treated with conservative management. The prognosis is good for patients who survive the initial dissection and are treated in this manner. It is important to obtain a thorough history of young and healthy patients who present with concerning neurologic symptoms so that precipitating activities are not missed.