More than 30 years ago, Cincinnati Children’s Hospital Medical Center implemented an international screening program for genetic causes of cholestatic liver disease that led to the identification of six new defects in bile acid synthesis. These conditions are fatal if not treated, causing idiopathic neonatal cholestatic syndromes and accounting for 2-5% of pediatric liver diseases. To make matters worse, these defects can manifest in a variety of non-specific conditions including fat-soluble vitamin malabsorption syndromes, progressive cholestatic disease, or neurological disease.
As yesterday’s plenary speaker Kenneth Setchell, PhD, pointed out, defects in bile acid synthesis “represent a distinct category of liver disease that, if left untreated, can be fatal.” He emphasized that “it was a real challenge to measure [bile acids] back then.”
Then, things changed. Setchell’s team discovered bile acid synthetic defects as a cause of progressive cholestatic liver disease, a success he attributes exclusively to the application of mass spectrometry in the 1980s. He outlined his journey with mass spectrometry from discovery of the disease to treatment in his plenary talk on Monday morning, “Genetic Defects in Bile Acid Synthesis Causing Liver Disease— Diagnosis and Treatment—Translational Medicine from Mass Spectrometry Discovery to the Bedside.”
The advances leading to Setchell’s work began with fast atom bombardment ionization mass spectrometry (FAB-MS)—a relatively new technique in 1978 when analysis of bile acids by MS was first demonstrated. This soft-ionization technique was soon replaced by electrospray ionization (ESI), which greatly simplified the process of analyzing bile acids in biological samples. During this time, faster and more automated methods for bile acid analysis also became available with the introduction of enzyme and immuno-based assays. However, these do not provide any structural information and are therefore unhelpful in differentiating metabolic defects in synthesis. Importantly, gas chromatography-MS or ESI-MS can distinguish different positional or stereo-isomers and offer confirmatory evidence of a potential biochemical defect. This analytical breakthrough led to a concerted effort to screen for bile acid defects in children and infants presenting with idiopathic liver disease.
Presenting a series of pediatric clinical cases, Setchell walked the audience through his fascinating molecular investigation of the causes of cholestasis using FAB. Bile acid excretion in healthy adults and children is relatively low, typically less than 20 µmol/L. This makes bile acid measurement in urine helpful to rule out a genetic defect in the cholesterol-bile acid pathway as the cause of idiopathic liver disease. Furthermore, the presence of the primary bile acid conjugates in urine indicates that pathways are intact, while accumulation of atypical bile acids is potentially hepatotoxic.
In the setting of bile acid disorders, liver injury occurs due to a failure to synthesize primary bile acids that are essential for bile acid-dependent bile flow and production of atypical metabolites. Setchell also discussed treatment of these variable disorders by administering cholic acid, which focuses on downregulating bile acid synthesis and ensuring that sufficient levels of primary bile acids are maintained for adequate bile flow.
“There is a big paradox here,” he said. “Our liver produces four bile acids that are toxic to our liver if not excreted in bile.” Setchell’s colleagues cautioned him that the idea of administering bile acids to a patient with liver disease was dangerous. But armed with molecular understanding of the pathophysiology of the disease and insights from mass spectrometery, Setchell persisted. His persistence paid off in March, 2015, when the Food and Drug Administration (FDA) approved Cholbam, a cholic acid formulation marketed by the company Setchell co-founded, to treat rare bile acid synthesis disorders.
This session was an elegant presentation of Setchell’s molecular investigation work and the fundamental role mass spectrometry played in the entire process. Setchell offered a few words of wisdom to the younger generation of scientists in the audience: “The key word is persistence,” he said. “You have to be persistent in research. Ours lasted through six presidential terms, from 1981 when we published our first abstract…to 2006, when we co-founded the company to get this therapy approved by the FDA, which finally happened in 2015.”