Metabolomic Profiling of Portal Blood and Bile Reveals Metabolic Signatures of Primary Sclerosing Cholangitis

Abstract

Primary sclerosing cholangitis (PSC) is a pathogenically complex, chronic, fibroinflammatory disorder of the bile ducts without known etiology or effective pharmacotherapy. Emerging in vitro and in vivo evidence support fundamental pathophysiologic mechanisms in PSC centered on enterohepatic circulation. To date, no studies have specifically interrogated the chemical footprint of enterohepatic circulation in PSC. Herein, we evaluated the metabolome and lipidome of portal venous blood and bile obtained at the time of liver transplantation in patients with PSC (n = 7) as compared to individuals with noncholestatic, end-stage liver disease (viral, metabolic, etc. (disease control, DC, n = 19)) and to nondisease controls (NC, living donors, n = 12). Global metabolomic and lipidomic profiling was performed on serum derived from portal venous blood (portal serum) and bile using ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and differential mobility spectroscopy-mass spectroscopy (DMS-MS; complex lipid platform). The Mann–Whitney U test was used to identify metabolites that significantly differed between groups. Principal-component analysis (PCA) showed significant separation of both PSC and DC from NC for both portal serum and bile. Metabolite set enrichment analysis of portal serum and bile demonstrated that the liver-disease cohorts (PSC and DC) exhibited similar enrichment in several metabolite categories compared to NC. Interestingly, the bile in PSC was uniquely enriched for dipeptide and polyamine metabolites. Finally, analysis of patient-matched portal serum and biliary metabolome revealed that these biological fluids were more homogeneous in PSC than in DC or NC, suggesting aberrant bile formation and enterohepatic circulation. In summary, PSC and DC patients exhibited alterations in several metabolites in portal serum and bile, while PSC patients exhibited a unique bile metabolome. These specific alterations in PSC are amenable to hypothesis testing and, potentially, therapeutic pharmacologic manipulation.

Alterations of the bile microbiome in primary sclerosing cholangitis

“…Furthermore, the extensive loss of function in the PSC bile fluid communities might reflect a decline of beneficial microbial contribution to bile duct mucosal homeostasis. This result may relate to the recent discovery of an altered bile metabolome in PSC 35…”

Lipid antigens in bile from patients with chronic liver diseases activate natural killer T cells

“…Bile is secreted by hepatocytes with subsequent modification by cholangiocytes and contains lipids of both endogenous origin (i.e. phospholipids and cholesterol) as well as microbial and xenobiotic compounds [21,41]. NKT cells recognize a broad spectrum of self and foreign antigens such as glycolipids, phospholipids, microbial antigens and even self‐peptide antigens [42].…”

“…Although the presence of biliary lipid antigens was detected using murine NKT hybridomas, human and murine NKT cells show a high level of conservation [7] and there is an overlap of activating lipids between human and murine NKT cells [43], and mechanisms for molecular recognition are conserved [44,45]. Among the previously described classes of lipids in bile [21,41], the iNKT hybridoma 24.8 has been found to be responsive to phosphatidylinositol (PI), phosphatidylglycerol (PG), phosphatidylcholine PC, phosphatidylethanolamine (PE), sphingomyelin (SM), the niNKT hybridoma 14S.6 has been found to respond to PI, PG, PE, lysophosphatidylcholine (LPC) and lysophosphatidylethanolamine (LPE) and the niNKT hybridoma 14S.7 has been found to respond to PI [14,23,46]. Thus, the activating lipids found in our experiments probably belong to one of these classes.…”

“…Bile is rich in lipids and contains several classes of lipids known to activate NKT cells, but to our knowledge a direct immunological role of such lipid antigens has not been demonstrated [21]. Herein, we report the probable presence of antigens in bile that are potentially of host and microbial origin which are capable of activating NKT cells implicating a potential role in biliary immunopathology.…”

Cell Interactions in Biliary Diseases: Clues from Pathophysiology and Repair Mechanisms to Foster Early Assessment

“…As aforementioned, enterohepatic circulation, resulting in a bidirectional exchange of bioactive compounds, including endogenous (bile components) and exogenous metabolites (nutrients, xenobiotics, and gut bacteria) between the gut and the liver, is a central pathogenetic mechanism of the initiation and progression of cholestasis in several biliary disorders, particularly in PSC. By performing global metabolomic and lipidomic analysis in the portal serum and bile of patients with PSC, compared with noncholestatic chronic liver diseases, and of healthy controls, Tietz-Bogert and Kim et al found that the bile in PSC had a unique and more homogeneous profile, enriched in dipeptides and polyamine metabolites, which can alter liver cell homeostasis as well as the intestinal microbiota [17]. Interestingly, polyamine catabolism has been associated with intense generation of reactive oxygen species, which represent an important determinant of disease progression in PSC.…”