Disposition of isosteviol in the rat isolated perfused liver

Abstract

1. The aim of the present study was to investigate the mechanisms involved in the clearance of isosteviol using the rat isolated perfused liver. 2. Six livers from male Sprague-Dawley rats were perfused with 15.7 mumol isosteviol in a recirculating system. Perfusate and bile samples were collected for 60 min and the liver was collected at the end of the perfusion. All samples collected were incubated with alpha-glucuronidase. Isosteviol-glucuronide was determined as equivalent isosteviol. Isosteviol concentrations were determined using a previously developed liquid chromatography-tandem mass spectrometry method. The final isosteviol liver/perfusate (L/P), bile/liver (B/L) and isosteviol-glucuronide in bile/liver (B(G)/L(G)) ratios were determined. 3. Isosteviol has a high clearance (21.4 +/- 4.8 mL/min) from the perfusate, with a short half-life (13 +/- 4 min). alpha-Glucuronidase incubation revealed that isosteviol is conjugated in the liver and excreted into the bile. There was no isosteviol-glucuronide detected in perfusate samples. The total recovery of the rat isolated perfused liver system is 74 +/- 14% and glucuronidated isosteviol accounted for 23 +/- 4% of the administered dose. 4. In conclusion, we are the first to characterize the metabolism of isosteviol using rat isolated liver perfusion. Our results strongly suggest that the liver is the main organ of isosteviol elimination and that isosteviol is glucuronidated in the liver before it is excreted into the bile.

Dose‐dependent pharmacokinetics and tentative identification of urine metabolites from an isosteviol derivative with anti‐hepatitis B activity in rats

“…Phase II metabolic reactions suggested by the data were glucuronidation and bis ‐glucuronidation of M2 and M3 to respectively yield M4 and M5 (Holčapek et al, ; Levsen et al, ). Isosteviol was also shown to undergo glucuronidation at the C‐19 oxygen in the isolated perfused rat liver (Jin, Wang, Gerber, & Davey, ). While glucuronidation may occur at the S, C, N and O atoms of drugs, it should be noted that the mass spectrum data alone might be inadequate to ascertain whether N or O glucuronidation occurred in the metabolism of compound 1 in this study (Hawes, ).…”