The history of bile acids is a remarkable journey spanning more than two millennia, from the apothecary traditions of ancient China to the sophisticated pharmaceutical pipelines of the 21st century. What began as an empirical understanding of animal bile has evolved, through centuries of scientific enquiry, into one of the most clinically significant and therapeutically versatile classes of molecules in modern medicine.
Today, bile acid science sits at the heart of treatments for liver disease, gallstone dissolution, and emerging therapies for metabolic disorders. The story of how we arrived here is as compelling as the chemistry itself.
Ancient Origins: Bile in Traditional Chinese Medicine
Long before scientists had the tools to isolate or characterise individual molecules, practitioners of Traditional Chinese Medicine (TCM) had identified animal bile as a valuable therapeutic substance. The use of bear bile is documented as far back as 659 CE in the Tang Ben Cao (Newly Revised Materia Medica), one of the most important pharmacological texts of the Tang Dynasty.
Within the framework of TCM, bear bile was described as being able to “clear heat” and “relieve toxin”. While these concepts are distinct from modern biomedical terminology, contemporary research has identified anti-inflammatory and hepatoprotective properties in ursodeoxycholic acid (UDCA), one of the major bile acids found in bear bile.
Bear bile was prescribed for a variety of conditions, including:
- Jaundice and liver disorders
- Eye ailments
- Haemorrhoids
- Inflammatory conditions
Over centuries of practice, bear bile earned the designation “king of animal biles” among many TCM practitioners. Modern chemical analysis suggests that its perceived therapeutic value may be related, at least in part, to the unusually high concentration of ursodeoxycholic acid (UDCA) found in bear bile. Other animal biles, including those derived from cattle, pigs, snakes, and chickens, also featured prominently in traditional pharmacopoeias, each recognised as possessing distinct medicinal properties.
This diversity of use reflects a form of observation-led pharmacology that, while lacking the analytical tools of modern chemistry, was nevertheless grounded in genuine biological activity.
The Birth of Modern Bile Acid Chemistry
The transition from traditional knowledge to scientific understanding began in earnest during the early twentieth century.
German chemist Heinrich Otto Wieland played a central role in this transformation. Beginning his investigations into bile acids in 1912, Wieland and his collaborators undertook a series of painstaking chemical studies to determine the structures of cholic acid and related compounds. Their work revealed that bile acids belong to the steroid family of molecules and share a close structural relationship with cholesterol, fundamentally reshaping scientific understanding of lipid biochemistry.
For these discoveries, Wieland was awarded the 1927 Nobel Prize in Chemistry for his investigations into the constitution of bile acids and related substances.
Key milestones from this period include:
- 1912 – Wieland begins systematic structural research on bile acids
- 1927 – Wieland receives the Nobel Prize in Chemistry; Japanese chemist Shoda isolates UDCA from bear bile
- 1928 – Adolf Windaus receives the Nobel Prize in Chemistry for his work on sterols and their relationship to vitamins
- 1936 – Iwasaki further characterises the structure of UDCA
- 1955 – Japanese researchers achieve laboratory synthesis of UDCA, enabling pharmaceutical production independent of animal sources
Together, Wieland and Windaus helped establish the structural relationship between bile acids, sterols, and cholesterol, laying the foundations for modern steroid chemistry and decades of subsequent pharmaceutical development.
What Are Bile Acids? A Brief Overview
Bile acids are steroid molecules synthesised in the liver from cholesterol. They are secreted into bile, stored in the gallbladder, and released into the small intestine during digestion, where they facilitate the absorption of dietary fats and fat-soluble vitamins.
Bile acids can be classified according to their carbon skeleton, although the compounds most relevant to human physiology and medicine are the C24 bile acids.
The two primary bile acids produced directly by the liver are:
- Cholic acid (CA)
- Chenodeoxycholic acid (CDCA)
Once secreted into the intestine, these molecules are modified by gut bacteria to produce secondary bile acids, including:
- Deoxycholic acid (DCA)
- Lithocholic acid (LCA)
Ursodeoxycholic acid (UDCA) is normally a minor component of the human bile acid pool but occurs at substantially higher levels in bear bile. It is this molecule that has become one of the most important therapeutic bile acids in modern medicine.
From Bench to Bedside: UDCA in Clinical Medicine
The laboratory synthesis of UDCA in 1955 opened the door to widespread clinical investigation.
Researchers soon discovered that UDCA could dissolve certain cholesterol gallstones by altering bile composition, providing a non-surgical treatment option for selected patients. As clinical evidence accumulated, its therapeutic applications expanded considerably.
UDCA exerts protective effects on liver and bile duct cells through multiple mechanisms and is commonly described as having:
- Anticholestatic properties that improve bile flow
- Anti-apoptotic effects that protect cells from premature death
- Anti-inflammatory activity
- Antifibrotic effects that may help limit liver scarring
Today, UDCA is the evidence-based first-line treatment for primary biliary cholangitis (PBC), the most common chronic cholestatic liver disease, and is approved in numerous jurisdictions worldwide for this indication.
UDCA has also been investigated and used in selected patients with primary sclerosing cholangitis (PSC), although its role remains considerably more controversial than in PBC. In addition, it is widely used in the management of intrahepatic cholestasis of pregnancy and several other cholestatic disorders.
Bile Acid Receptors and a New Therapeutic Era
One of the most transformative discoveries in modern bile acid biology has been the recognition that bile acids function not only as digestive molecules but also as signalling molecules.
Bile acids interact with receptors throughout the body, influencing metabolism, inflammation, immune function, and energy homeostasis. This insight has opened entirely new avenues for pharmaceutical development.
Two receptors are of particular significance:
Farnesoid X Receptor (FXR)
FXR is a nuclear receptor that regulates bile acid synthesis, transport, and homeostasis. Activation of FXR influences multiple pathways involved in inflammation, fibrosis, and metabolic regulation.
Obeticholic acid (OCA), a semisynthetic derivative of chenodeoxycholic acid, received regulatory approval in 2016 as a second-line treatment for PBC, representing the first new approved therapy for the disease in more than two decades.
TGR5 (GPBAR1)
TGR5 is a G protein-coupled receptor expressed in the gut, liver, immune cells, and other tissues.
Activation of TGR5 has demonstrated promising metabolic effects in preclinical and early clinical research, making it an attractive target for future therapies aimed at conditions such as metabolic syndrome, type 2 diabetes, and metabolic dysfunction-associated steatohepatitis (MASH).
Bile Acids, the Gut Microbiome, and Emerging Frontiers
One of the most dynamic areas of contemporary research concerns the relationship between bile acids and the gut microbiome.
The intestinal microbiota plays a critical role in converting primary bile acids into secondary bile acids, while the composition of the bile acid pool influences the structure and function of microbial communities within the gut. This bidirectional relationship has linked bile acid biology to a wide range of physiological and pathological processes.
Researchers are investigating how bile acid–microbiome interactions may contribute to:
- Inflammatory bowel disease
- Obesity and metabolic disorders
- Cardiovascular disease
- Liver disease
- Neurological and neuropsychiatric processes through the gut–brain axis
Particularly noteworthy is ongoing research into tauroursodeoxycholic acid (TUDCA), a conjugated bile acid derivative that has demonstrated neuroprotective effects in preclinical studies. Investigators continue to explore its potential relevance to neurodegenerative and neuropsychiatric disorders.
While many of these applications remain under active investigation, they highlight the expanding therapeutic significance of bile acid biology beyond the digestive system.
A Continuum from Ancient Wisdom to Modern Science
The history of bile acids illustrates the long and often surprising dialogue between empirical observation and scientific discovery.
The practitioners who recognised the medicinal value of animal bile centuries ago could not have known the molecular structures involved, nor the complex receptor networks that modern researchers continue to uncover. Yet many of the biological effects they observed would eventually be explained through advances in chemistry, biochemistry, pharmacology, and clinical medicine.
The structural insights achieved by Wieland, Windaus, and their contemporaries laid the foundations for synthetic manufacturing programmes that now produce UDCA and related compounds at industrial scale. Meanwhile, modern research continues to reveal new functions for bile acids as signalling molecules involved in metabolism, immunity, and human health.
Today, bile acids represent far more than digestive detergents. They are a scientifically rich and therapeutically important class of molecules whose story continues to evolve, linking ancient medical traditions with some of the most promising areas of modern pharmaceutical research.
At ICE Pharma, we have dedicated over 70 years to the development and manufacture of bile acid derivatives. Understanding where these molecules have come from, scientifically and historically, is part of what drives our commitment to advancing where they are going next.