24-Norursodeoxycholic acid in patients with primary sclerosing cholangitis: A new "urso saga" on the horizon?

Bile Acids-A Peek Into Their History and Signaling

Bile acids wear many hats, including those of an emulsifier to facilitate nutrient absorption, a cholesterol metabolite, and a signaling molecule in various tissues modulating itching to metabolism and cellular functions. Bile acids are synthesized in the liver but exhibit wide-ranging effects indicating their ability to mediate organ-organ crosstalk. So, how does a steroid metabolite orchestrate such diverse functions? Despite the inherent chemical similarity, the side chain decorations alter the chemistry and biology of the different bile acid species and their preferences to bind downstream receptors distinctly. Identification of new modifications in bile acids is burgeoning, and some of it is associated with the microbiota within the intestine. Here, we provide a brief overview of the history and the various receptors that mediate bile acid signaling in addition to its crosstalk with the gut microbiota.

Gene Therapy for Acquired and Genetic Cholestasis

Cholestatic diseases can be caused by the dysfunction of transporters involved in hepatobiliary circulation. Although pharmacological treatments constitute the current standard of care for these diseases, none are curative, with liver transplantation being the only long-term solution for severe cholestasis, albeit with many disadvantages. Liver-directed gene therapy has shown promising results in clinical trials for genetic diseases, and it could constitute a potential new therapeutic approach for cholestatic diseases. Many preclinical gene therapy studies have shown positive results in animal models of both acquired and genetic cholestasis. The delivery of genes that reduce apoptosis or fibrosis or improve bile flow has shown therapeutic effects in rodents in which cholestasis was induced by drugs or bile duct ligation. Most studies targeting inherited cholestasis, such as progressive familial intrahepatic cholestasis (PFIC), have focused on supplementing a correct version of a mutated gene to the liver using viral or non-viral vectors in order to achieve expression of the therapeutic protein. These strategies have generated promising results in treating PFIC3 in mouse models of the disease. However, important challenges remain in translating this therapy to the clinic, as well as in developing gene therapy strategies for other types of acquired and genetic cholestasis.

The Management of Cholestatic Liver Diseases: Current Therapies and Emerging New Possibilities

Primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) are two chronic cholestatic liver diseases affecting bile ducts that may progress to biliary cirrhosis. In the past few years, the increasing knowledge in the pathogenesis of both diseases led to a growing number of clinical trials and possible new targets for therapy. In this review, we provide an update on the treatments in clinical use and summarize the new drugs in trials for PBC and PSC patients. Farnesoid X Receptor (FXR) agonists and Pan-Peroxisome Proliferator-Activated Receptor (PPAR) agonists are the most promising agents and have shown promising results in both PBC and PSC. Fibroblast Growth Factor 19 (FGF19) analogues also showed good results, especially in PBC, while, although PBC and PSC are autoimmune diseases, immunosuppressive drugs had disappointing effects. Since the gut microbiome could have a potential role in the pathogenesis of PSC, recent research focused on molecules that could change the microbiome, with good results. The near future of the medical management of these diseases may include new treatments or a combination of multiple drugs targeting different signaling pathways at different stages of the diseases.

UDCA, NorUDCA, and TUDCA in Liver Diseases: A Review of Their Mechanisms of Action and Clinical Applications

Bile acids (BAs) are key molecules in generating bile flow, which is an essential function of the liver. In the last decades, there have been great advances in the understanding of BA physiology, and new insights have emerged regarding the role of BAs in determining cell damage and death in several liver diseases. This new knowledge has helped to better delineate the pathophysiology of cholestasis and the adaptive responses of hepatocytes to cholestatic liver injury as well as of the mechanisms of injury of biliary epithelia. In this context, therapeutic approaches for liver diseases using hydrophilic BA (i.e., ursodeoxycholic acid, tauroursodeoxycholic, and, more recently, norursodeoxycholic acid), have been revamped. In the present review, we summarize current experimental and clinical data regarding these BAs and its role in the treatment of certain liver diseases.