Pyridoxal isonicotinoyl hydrazone (PIH) has recently been identified as a new
iron chelating agent with a high degree of
iron mobilizing activity in vitro and in vivo which makes this compound a candidate
drug in the treatment of
iron overload. This study was undertaken to elucidate the mechanism of action of the
iron mobilizing activity of PIH at the cellular level. An in vitro system of rabbit reticulocytes with a high level of non-
heme 59Fe was used as a model of
iron overload. The effects of various biochemical and physiological maneuvers on the mobilization of 59Fe by PIH from the cells were studied. The fate of [14C]-PIH in the in vitro system was also studied. Studies were also carried out using a crude mitochondrial fraction. The results indicate three phases in the
iron mobilizing activity of PIH: (1) the entry of PIH into erythroid cells seems to be by passive diffusion; (2) chelation occurs mainly from mitochondria and may depend on the availability of
iron in a low molecular weight, non-
heme pool. Chelation seems to be enhanced by reduction of Fe (III) to Fe (II); (3) the exit of the PIH2-Fe complex is an energy-dependent process.
Iron mobilization by PIH is not dependent on (Na+ + K+)-
ATPase activity, external ionic composition, or external hydrogen ion concentration. Membrane fluidity does not seem to play a role in PIH-Fe mobilization. The exit of the PIH2-Fe complex is inhibited by anti-microtubule agents (
vinca alkaloids but not
colchicine) suggesting that the PIH2-Fe complex is actively extruded from the cell by a microtubule-dependent event.