Protein binding and α : β anomer ratio of dihydroartemisinin in vivo

Aims

To determine the ratio of α : β anomers and the protein binding of dihydroartemisinin (DHA) in vivo.

Methods

10‐[³H]‐DHA was synthesized by reduction of artemisinin with sodium boro‐[³H]‐hydride and purified with preparative thin layer chromatography. A solution of ³H‐DHA (2000 ng in 20 µl) was added to 2 ml whole blood from 15 healthy volunteers and 22 Vietnamese patients with falciparum or vivax malaria. The blood was centrifuged and the plasma stored at −25 °C until analysed by HPLC with radiochromatographic detection. Protein‐free ultrafiltrate of the plasma was assayed to determine the free fraction of DHA and the in vivo ratio of α‐DHA : β‐DHA.

Results

The DHA fraction unbound (mean ± SD) was 0.068 ± 0.032 in Vietnamese patients with falciparum malaria (n = 17), 0.065 ± 0.009 in Vietnamese patients with vivax malaria (n = 5), 0.117 ± 0.015 in Vietnamese volunteers (n = 7) and 0.092 ± 0.020 in Caucasian volunteers (n = 8). The ratios of α‐DHA : β‐DHA for the four groups were 6.3 ± 0.9, 6.9 ± 0.8, 6.9 ± 0.6 and 5.4 ± 0.8, respectively.

Conclusions

DHA is approximately 93% protein‐bound in patients with malaria infection and there is a preferential existence in vivo of the α‐DHA anomer. Knowledge of this stereochemistry may be valuable in elucidation of the mechanisms of DHA action and/or toxicity, and in the synthesis of new trioxane antimalarials.

DOI: 10.1046/j.1365-2125.2003.02045.x

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