Enterohepatic circulation of scymnol sulfate in an elasmobranch, the little skate (Raja erinacea)

Abstract

The sulfated bile alcohol scymnol sulfate (ScyS), 3α,7α,12α,24ξ,26,27-hexahydroxy-5β-cholestane-26(27)-sulfate, is the major bile salt in bile of an elasmobranch, the little skate. To investigate hepatic transport of bile alcohols in skate liver, [3H]ScyS and a potential precursor, 3α,7α,12α-trihydroxy-5β-cholestane (chtriol), were used as model compounds. Their transport into isolated hepatocytes was partially saturable, temperature sensitive, and Na+ independent. The uptake of ScyS was inhibited by cholyltaurine, and uptake of cholyltaurine was inhibited by ScyS in a competitive manner. In contrast, uptake of chtriol was not inhibited by cholyltaurine, suggesting separate transport systems. ScyS and chtriol showed a choleretic effect in isolated perfused livers. When ScyS was added to the perfusate of isolated perfused livers, >25% was found in bile within 7 h. When chtriol was added to the perfusate, 10% of the dose was secreted into the bile mainly in the form of polar metabolites, whereas only nonmetabolized chtriol remained in the livers. The slow bile flow of 40–50 μl/h and the high recovery in the liver suggest that metabolism may be the rate-limiting step in the hepatic elimination of chtriol. The major metabolites secreted into bile were identified by mass spectrometry and chromatography as scymnol and ScyS. To study the enterohepatic circulation, [3H]ScyS or [3H]chtriol was administered into the duodenum of free-swimming skates, and bile was collected through exteriorized indwelling cannulas over a 4-day period. More than 90% of the radioactivity was recovered from bile, indicating that there was a highly effective absorption in the intestinal epithelium, as well as specific transport mechanisms for hepatic uptake and biliary secretion of these compounds. This is the first direct demonstration of an enterohepatic circulation for a bile alcohol sulfate in fish liver.

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

“…5␤-Scymnol sulfate undergoes vectorial hepatocyte transport by basolateral and apical transporters related to those that mediate the hepatocyte transport of C 24 bile acids in mammals (45). 5␣-Cyprinol sulfate, which we found to be present in gallbladder bile at the high concentration of 0.3 M, has been shown to be the toxic constituent of carp bile (16).…”

Evolution of substrate specificity for the bile salt transporter ASBT (SLC10A2)

“…Previous work by our group demonstrated that bile salts are reabsorbed from the intestine of the little skate, suggesting that an active transport system is present for bile salts (21). However, it was not known if this transport system is Na + -dependent, as is human and rodent ASBT/Asbt.…”

Expression cloning of two genes that together mediate organic solute and steroid transport in the liver of a marine vertebrate

“…This observation is physiologically relevant because skates appear to excrete sterols mainly as sulfate conjugates (46,47). The major bile salt in skate bile is scymnol sulfate, a sulfated bile alcohol that is rapidly removed from hepatic portal blood and transported into bile (47,48). The overall substrate specificity of Ost␣͞Ost␤ is most similar to that of the OATP family of Osts (1,4), and in particular to that of human OATP-C (also known as LST1 and OATP-2).…”