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The rat biliary metabolites of dihydroartemisinin, an antimalarial endoperoxide
J L Maggs1, S Madden, L P Bishop
1Department of Pharmacology and Therapeutics, University of Liverpool, Liverpool, UK.
Abstract:
[13-14C]Dihydroartemisinin was administered to male rats (35 micromol kg-1, iv). Within 0-1 hr and 0-5 hr of dosing, 34.8 +/- 5. 2% (mean +/- SD, N = 6) and 48.4 +/- 5.9% of the radiolabel, respectively, was recovered in bile. Only 1.1 +/- 1.2% was recovered in bladder urine after 5 hr. The biliary metabolites were identified by LC/MS. The principal metabolite (21.1 +/- 9.3% of dose) was the biologically inactive dihydroartemisinin (DHA) glucuronide. The other metabolites were products of reductive cleavage and rearrangement of the endoperoxide bridge, a process known to generate reactive radical intermediates and abolish antimalarial activity. They were desoxy-DHA (3.3 +/- 2.0%) and its glucuronide (1.1 +/- 1.0%), 3-hydroxydesoxy-DHA glucuronide (2.9 +/- 1.8%), and the glucuronide of a ring-contracted tetrahydrofuran acetate isomer of DHA (6.9 +/- 5.6%).
Insights
Dihydroartemisinin is primarily excreted in bile as an inactive glucuronide in rats. Other metabolites result from endoperoxide bridge cleavage, potentially generating reactive intermediates and reducing antimalarial activity.
Area of Science:
- Pharmacokinetics and Drug Metabolism
- Medicinal Chemistry
- Toxicology
Background:
- Dihydroartemisinin (DHA) is a key antimalarial drug.
- Understanding DHA metabolism is crucial for optimizing its therapeutic use and safety.
- Biliary excretion and metabolic pathways of DHA are not fully elucidated.
Purpose of the Study:
- To investigate the metabolic fate and excretion pathways of [13-14C]dihydroartemisinin in male rats.
- To identify and quantify the major biliary metabolites of DHA.
- To explore the implications of DHA metabolism on its antimalarial activity and potential toxicity.
Main Methods:
- Administration of radiolabeled dihydroartemisinin ([13-14C]DHA) intravenously to male rats.
- Collection and analysis of bile and urine samples over a 5-hour period.
- Identification of biliary metabolites using Liquid Chromatography-Mass Spectrometry (LC/MS).
Main Results:
- Significant recovery of radiolabel in bile (48.4% within 5 hours), with minimal excretion in urine (1.1%).
- The principal biliary metabolite was identified as the inactive dihydroartemisinin glucuronide (21.1% of dose).
- Other metabolites included desoxy-DHA, its glucuronide, 3-hydroxydesoxy-DHA glucuronide, and a glucuronide of a ring-contracted isomer, all resulting from endoperoxide bridge cleavage.
Conclusions:
- Biliary excretion is the primary route for dihydroartemisinin elimination in rats.
- Metabolism involves glucuronidation and reductive cleavage of the endoperoxide bridge, leading to biologically inactive compounds.
- The formation of reactive intermediates during reductive cleavage may contribute to toxicity and loss of antimalarial efficacy.