Free radicals formed by addition of antimalaric artemisinin (Qinghaosu, QHS) to human serum: an ESR-spin trapping investigation

The antimalaric drug artemisinin (QHS) is believed to operate through a mechanism initiated with the cleavage of its endoperoxidic bond induced by transition metal ions. An ESR investigation of the reaction of QHS with human serum in the presence of two spin trapping agents has led to the detection of spin adducts of carbon-centred radicals. Experiments carried out replacing the human serum with iron(II) salts led to the observation of the same spin adducts, thus supporting previous suggestions that also in vivo the drug operates via a radical-based mechanism. UV irradiation of QHS also led to the trapping of transient free radicals.