Hepatic handling of a synthetic γ-labeled bile acid (75SeHCAT)

⁷⁵Se-homocholic acid-taurine (⁷⁵SeHCAT) is the first available γ-labeled bile acid, and should therefore be handled more efficiently and specifically by the liver than previous hepatoscintigraphic agents. We have measured serum and hepatic kinetics for ⁷⁵SeHCAT, and compared them with those for the conventional hepatobiliary scintigraphic agent ^99mTc-hepatoiminodiacetic acid, and with serum kinetics for the corresponding natural bile acid, [¹⁴C]cholic acid-taurine. We used a dynamic scintigraphic technique and serial blood sampling in 8 subjects. Initial hepatic uptake rate was identical to initial serum disappearance rate (14% dose/min) for ⁷⁵SeHCAT, but significantly lower for ^99mTchepatoiminodiacetic acid (6% vs. 14% dose/min, p <0.001). Hepatic transit time was shorter for ⁷⁵SeHCAT (13 min vs. 22 min, p <0.02), net hepatic excretory rate was more rapid (1.4% vs. 0.8% dose/min, p <0.001), and urinary excretion was lower (1.0% vs. 9.0% dose, p <0.001). Initial and late plasma disappearance rates were significantly lower for ⁷⁵SeHCAT (14.3% and 1.5% dose/min) than for [¹⁴C]cholic acid-taurine (21.3% and 2.8% dose/min, respectively), and plasma clearance was also lower (275 vs. 670 ml/min). In vitro, ⁷⁵SeHCAT was bound to serum proteins more completely than [¹⁴C]cholic acid-taurine (90.4% vs. 86.5%, p75SeHCAT provides a hepatoscintigraphic agent that is handled more efficiently and specifically by the liver than the conventionally used agent ^99mTc-hepatoiminodiacetic acid. It is not cleared from the serum as rapidly as [¹⁴C]cholic acid-taurine, probably due to its stronger protein binding. The clinical value of ⁷⁵SeHCAT in assessing liver disease should be investigated.