There have been numerous recent reports of the ability of hemin (ferric chloride protoporphyrin IX) to induce differentiation in several hematopoietic and non-hematopoietic cell lines. These reports have not addressed the mechanism by which hemin is transported into these cells, thereby permitting the various heme-dependent changes to occur. Recent work in our laboratory has demonstrated that hemin will also protect cells in culture from the damaging effects of exposure to certain anthracyclines. Again, in these studies, the transport of hemin into those compartments where the protective effects may occur has not been examined. In many cell compartments anthracyclines are toxic because of generation of hydroxyl radicals. The effect of hemin on the formation of active oxygen species is also unexplored. Hemin transport has been studied primarily in hepatocytes. The physiologic mechanisms for heme transport and delivery to hepatocytes is via hemopexin (HP). Specific receptors for HP on hepatocytes mediate the uptake of heme into the hepatocyte. Similar HP receptors and receptor-mediated heme uptake from HP have not yet been described in other cells. The primary aims of this study are: (1) to examine heme binding and uptake in two hematopoietic cell lines, the human leukemia K-562 and mouse erythroleukemia (MEL) lines, both of which are markedly influenced by hemin. This will involve determining binding and uptake of free heme by the cells and binding and uptake of heme bound to hemopexin with particular attention to evaluating the existence of a specific H-HP receptor system on the cell surface; and (2) to investigate the interaction of heme and anthracyclines with particular attention to heme-hemopexin binding, heme transport, anthracycline uptake, and heme inactivation of anthracycline-induced active oxygen species. (M)
