Inhibition of Fe2+- and Fe3+- induced hydroxyl radical production by the iron-chelating drug deferiprone

Deferiprone (L1) is an effective iron-chelating drug that is widely used for the treatment of iron-overload diseases. It is known that in aqueous solutions Fe²⁺ and Fe³⁺ ions can produce hydroxyl radicals via Fenton and photo-Fenton reactions. Although previous studies with Fe²⁺ have reported ferroxidase activity by L1 followed by the formation of Fe³⁺ chelate complexes and potential inhibition of Fenton reaction, no detailed data are available on the molecular antioxidant mechanisms involved. Similarly, in vitro studies have also shown that L1–Fe³⁺ complexes exhibit intense absorption bands up to 800 nm and might be potential sources of phototoxicity. In this study we have applied an EPR spin trapping technique to answer two questions: (1) does L1 inhibit the Fenton reaction catalyzed by Fe²⁺ and Fe³⁺ ions and (2) does UV–Vis irradiation of the L1–Fe³⁺ complex result in the formation of reactive oxygen species. PBN and TMIO spin traps were used for detection of oxygen free radicals, and TEMP was used to trap singlet oxygen if it was formed via energy transfer from L1 in the triplet excited state. It was demonstrated that irradiation of Fe³⁺ aqua complexes by UV and visible light in the presence of spin traps results in the appearance of an EPR signal of the OH spin adduct (TMIO–OH, a(N)=14.15 G, a(H)=16.25 G; PBN–OH, a(N)=16.0 G, a(H)=2.7 G). The presence of L1 completely inhibited the OH radical production. The mechanism of OH spin adduct formation was confirmed by the detection of methyl radicals in the presence of dimethyl sulfoxide. No formation of singlet oxygen was detected under irradiation of L1 or its iron complexes. Furthermore, the interaction of L1 with Fe²⁺ ions completely inhibited hydroxyl radical production in the presence of hydrogen peroxide. These findings confirm an antioxidant targeting potential of L1 in diseases related to oxidative damage.