Physicochemical and physiological properties of 5α-cyprinol sulfate, the toxic bile salt of cyprinid fish

5α-Cyprinol sulfate was isolated from bile of the Asiatic carp, Cyprinus carpio. 5α-Cyprinol sulfate was surface active and formed micelles; its critical micellization concentration (CMC) in 0.15 M Na+ using the maximum bubble pressure device was 1.5 mM; by dye solubilization, its CMC was ∼4 mM. At concentrations >1 mM, 5α-cyprinol sulfate solubilized monooleylglycerol efficiently (2.1 molecules per mol micellar bile salt). When infused intravenously into the anesthetized rat, 5α-cyprinol sulfate was hemolytic, cholestatic, and toxic. In the isolated rat liver, it underwent little biotransformation and was poorly transported (Tmax ≅ 0.5 μmol/min/kg) as compared with taurocholate. 5α-Cyprinol, its bile alcohol moiety, was oxidized to its corresponding C27 bile acid and to allocholic acid (the latter was then conjugated with taurine); these metabolites were efficiently transported. 5α-Cyprinol sulfate inhibited taurocholate uptake in COS-7 cells transfected with rat asbt, the apical bile salt transporter of the ileal enterocyte. 5α-Cyprinol had limited aqueous solubility (0.3 mM) and was poorly absorbed from the perfused rat jejunum or ileum. Sampling of carp intestinal content indicated that 5α-cyprinol sulfate was present at micellar concentrations, and that it did not undergo hydrolysis during intestinal transit.These studies indicate that 5α-cyprinol sulfate is an excellent digestive detergent and suggest that a micellar phase is present during digestion in cyprinid fish.