264 MINIMAL MODEL TO DETERMINE FIRST-PASS HEPATIC EXTRACTION OF CHOLATE IN HUMANS

Purpose To mathematically model clearance curves of cholate administered intravenously (13C) and orally (2H) to patients with chronic hepatitis C (HALT-C cohort). Background First-pass hepatic extraction of cholate can be measured in humans after simultaneous oral and intravenous administration of dual isotopes. Cholate escaping hepatic extraction enters the systemic circulation and is defined by cholate shunt. In 286 patients with fibrotic stages of chronic hepatitis C, cholate shunt correlated with cirrhosis on liver biopsy, varices on endoscopy, splenomegaly on ultrasonography, platelet count, and biochemical markers of disease severity. However, the method of measuring cholate shunt required multiple samples of blood (n=14) collected over 3 hours. Methods 20 mg of 24-13C cholic acid was dissolved in NaHCO3, mixed with 5 ml 25% human albumin and injected through an intravenous catheter over 2 min. 40 mg of 2,2,4,4-2H cholic acid was dissolved in water and taken orally. Blood was drawn at baseline and 5, 10, 15, 20, 30, 45, 60, 75, 90, 105, 120, 150 and 180 minutes post-dose. The cholates were isolated by extraction from serum with Sep-Pak C18 cartridge, acidification, ether extraction, methylation, TMS derivatization, and capillary GC/MS isotope ratiometry. Cholate shunt was calculated as AUCoral/AUCiv × Doseiv/Doseoral × 100%. Results Deconvolutional analysis was performed on the 14-point intravenous and oral clearance curves to obtain the minimal amount of points and time period required to regenerate the full curves. We compared models ranging from 2 to 7 time points spanning time periods from 5 to 180 minutes. The optimum model was 5 time points bracketing inflection points in the clearance curves and encompassing a time period of 90 min. This analysis indicates that cholate shunt may be accurately determined from 5 samples of blood obtained at 5, 20, 45, 60 and 90 minutes post dose. The accuracy of the 5-point “minimal model” in measurement of cholate shunt was 98.1 ± 1.4% of that calculated using all 14 time points. Conclusion The 5-point model accurately defines cholate shunt. The reduced number of samples and decreased time period of sampling greatly improve the applicability of measuring cholate shunt in humans.