Elevated circulating bile acids driven erythrocyte osmotic resistance marks hepatobiliary disease

Cholemia [i.e., elevated circulating bile acids (BA)] is an early feature of hepatobiliary disorders. However, cholemia often goes undetected because BA are not measured in routine health screenings. We hypothesized that the membrane-disrupting properties of BA might impact red blood cell (RBC) osmotic resistance (OR), potentially providing a means to detect cholemia. To test this, RBC OR was examined in multiple mouse models of cholemia, germ-free animals, and patients with cholestatic liver disease. RBC from cholemic mice exhibited markedly elevated OR against hypotonic sodium chloride, potassium chloride, and ammonium chloride solutions. Elevated OR was observed in an array of mouse models of cholemia, including mice with spontaneous portosystemic shunts, deficiencies in aryl hydrocarbon receptor, multidrug resistance protein 2, and farnesoid X receptor. The degree of OR correlated with serum BA levels. RBC OR increased upon ex vivo treatment with cholemic plasma or unconjugated BA. Conversely, the absence of gut microbiota in germ-free animals was associated with reduced BA levels and decreased RBC OR. Colonizing gut microbiota into germ-free animals via cohousing increased their RBC OR. RBC from patients with cholestatic liver disease also displayed increased OR, indicating potential human relevance. The elevated cholesterol-to-phospholipid ratio in the membranes of RBC from both cholemic mice and humans suggests increased membrane rigidity. Consistent with this, treatment with dimethyl sulfoxide to enhance membrane permeability reduced RBC OR. Taken together, these findings provide proof-of-concept that increased RBC OR is associated with cholemia and may serve as a basis for a whole blood approach to its detection.NEW & NOTEWORTHY Elevated circulating bile acids are associated with increased red blood cell (RBC) resistance to osmotic hemolysis in mice and humans. This phenotype reflects bile acid-driven remodeling of RBC membranes and provides a basis for a whole blood assay to assess cholemia using small blood volumes.