Abstract
Purpose
The present study examined the underlying mechanism by which 4-hydroxyacetophenone (4-HA), a bioactive compound found in several medicinal herbs, exerts its potent stimulatory effects on hepatic bile secretion.
Methods
Bile flow, and biliary excretion of 4-HA, its metabolites, and inorganic electrolytes was examined in both normal Wistar rats and in TR- Wistar rats that have a congenital defect in the multidrug resistance-associated protein-2, Mrp2/Abcc2. The effects of 4-HA were also examined in animals treated with buthionine sulfoximine to decrease hepatic glutathione (GSH) levels.
Results
In normal rats, 4-HA dramatically increased bile flow rate, whereas it failed to exert a choleretic effect in TR- rats. This choleresis was not explained by increased biliary output of Na+, K+, Cl− or HCO3 −, or by increased biliary GSH excretion. Depletion of hepatic GSH with buthionine sulfoximine had no effect on the 4-HA-induced choleresis. HPLC analysis revealed that a single major compound was present in bile, namely.4-hydroxyacetophenone-4-O-β-glucuronide, and that the parent compound was not detected in bile. Biliary excretion of the glucuronide was directly correlated with the increases in bile flow. In contrast to normal rats, this 4-HA metabolite was not present in bile of TR− rats.
Conclusions
These results demonstrate that the major biliary metabolite of 4-HA in rats is the 4-O-β-glucuronide, a compound that is secreted into bile at high concentrations, and may thus account in large part for the choleretic effects of 4-HA. Transport of this metabolite across the canalicular membrane into bile requires expression of the Mrp2 transport protein.
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Abbreviations
- BADF:
-
bile acid dependent flow
- BAIF:
-
bile acid independent flow
- BSO:
-
buthionine sulfoximine
- GSH:
-
reduced glutathione
- Mrp2:
-
multidrug resistance-associated protein-2
- 4-HA:
-
4-hydroxyacetophenone
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Acknowledgments
We thank Mr. Sirichai Kositarat (Central Instrument Facility, Faculty of Science, Mahidol University) for his technical assistance with HPLC analysis of 4-hydroxyacetophenone-4-O-β-glucuronide in bile samples of normal Wistar and TR− rats.
This study was supported by grants from the Royal Golden Jubilee program (to CM), the Thailand Research Fund, a research team strengthening grant from BIOTEC, and grants DK48823 and ES01247 from the USA National Institutes of Health (to NB).
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Mahagita, C., Tanphichai, K., Suksamrarn, A. et al. 4-Hydroxyacetophenone-Induced Choleresis in Rats is Mediated by the Mrp2-Dependent Biliary Secretion of Its Glucuronide Conjugate. Pharm Res 23, 2603–2610 (2006). https://doi.org/10.1007/s11095-006-9097-z
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DOI: https://doi.org/10.1007/s11095-006-9097-z