Desferrioxamine is both an iron chelator and a lysosomotropic amine

Abstract

Iron regulatory protein 2 (IRP2) coordinates cellular regulation of iron metabolism by binding to iron responsive elements in mRNA. The protein is synthesized constitutively, but is rapidly degraded when iron stores are replete. Desferrioxamine has been widely used to block iron-dependent degradation of IRP2, presumably by inducing an intracellular iron deficiency. However, desferrioxamine is a weak basic alkylamine with pKa values of 8.32, 9.16, 9.94 and 11.44. Thus, we investigated whether desferrioxamine acts both as an iron chelator and as a lysosomotropic amine, such as chloroquine. Such amines accumulate in lysosomes and increase lysosomal pH, causing swelling of lysosomes and inhibition of lysosomal function. We exposed HEK293 cells to desferrioxamine or chloroquine and found that 100 μM desferrioxamine did induce swelling of lysosomes, although less than that caused by 150 μM chloroquine. Further, quantitative immunoblotting demonstrated that both chloroquine and desferrioxamine substantially increased intracellular IRP2 levels. Lysomotropic amines inhibit lysosomal proteases and also inhibit unloading of iron from the transferrin-transferrin receptor complex. Experiments in progress with specific protease inhibitors will allow dissection of these two potential mechanisms of action of chloroquine and desferrioxamine.